doc: add plug mappings for merge conflict resolution

feat(conflict): detect and resolve inline merge conflict markers

.luarc.json

@@ -1,7 +1,7 @@
 {
   "runtime.version": "Lua 5.1",
   "runtime.path": ["lua/?.lua", "lua/?/init.lua"],
-  "diagnostics.globals": ["vim"],
+  "diagnostics.globals": ["vim", "jit"],
   "workspace.library": ["$VIMRUNTIME/lua", "${3rd}/luv/library"],
   "workspace.checkThirdParty": false,
   "completion.callSnippet": "Replace"

README.md

@@ -17,7 +17,10 @@ syntax highlighting.
 - Background-only diff colors for any `&diff` buffer (`:diffthis`, `vimdiff`)
 - Vim syntax fallback for languages without a treesitter parser
 - Hunk header context highlighting (`@@ ... @@ function foo()`)
-- Configurable debouncing, max lines, and diff prefix concealment
+- Character-level (intra-line) diff highlighting for changed characters
+- Inline merge conflict detection, highlighting, and resolution keymaps
+- Configurable debouncing, max lines, diff prefix concealment, blend alpha, and
+  highlight overrides
 
 ## Requirements
 
@@ -40,12 +43,11 @@ luarocks install diffs.nvim
 
 ## Known Limitations
 
-- **Incomplete syntax context**: Treesitter parses each diff hunk in isolation
-  without surrounding code context. When a hunk shows lines added to an existing
-  block (e.g., adding a plugin inside `return { ... }`), the parser doesn't see
-  the `return` statement and may produce incorrect highlighting. This is
-  inherent to parsing code fragments—no diff tooling solves this without
-  significant complexity.
+- **Incomplete syntax context**: Treesitter parses each diff hunk in isolation.
+  To improve accuracy, `diffs.nvim` reads lines from disk before and after each
+  hunk for parsing context (`highlights.context`, enabled by default with 25
+  lines). This resolves most boundary issues. Set
+  `highlights.context.enabled = false` to disable.
 
 - **Syntax flashing**: `diffs.nvim` hooks into the `FileType fugitive` event
   triggered by `vim-fugitive`, at which point the buffer is preliminarily
@@ -62,12 +64,17 @@ luarocks install diffs.nvim
     compatible, but both plugins modifying line highlights may produce
     unexpected results
   - [`git-conflict.nvim`](https://github.com/akinsho/git-conflict.nvim) -
-    conflict marker highlighting may overlap with `diffs.nvim`
+    `diffs.nvim` now includes built-in conflict resolution; disable one or the
+    other to avoid overlap
 
 # Acknowledgements
 
 - [`vim-fugitive`](https://github.com/tpope/vim-fugitive)
 - [`codediff.nvim`](https://github.com/esmuellert/codediff.nvim)
 - [`diffview.nvim`](https://github.com/sindrets/diffview.nvim)
+- [`difftastic`](https://github.com/Wilfred/difftastic)
+- [`mini.diff`](https://github.com/echasnovski/mini.diff)
+- [`gitsigns.nvim`](https://github.com/lewis6991/gitsigns.nvim)
+- [`git-conflict.nvim`](https://github.com/akinsho/git-conflict.nvim)
 - [@phanen](https://github.com/phanen) - diff header highlighting, unknown
-  filetype fix, shebang/modeline detection
+  filetype fix, shebang/modeline detection, treesitter injection support

doc/diffs.nvim.txt

@@ -20,6 +20,7 @@ Features: ~
 - Blended diff background colors that preserve syntax visibility
 - Optional diff prefix (`+`/`-`/` `) concealment
 - Gutter (line number) highlighting
+- Inline merge conflict marker detection, highlighting, and resolution
 
 ==============================================================================
 REQUIREMENTS                                              *diffs-requirements*
@@ -56,6 +57,11 @@ Configuration is done via `vim.g.diffs`. Set this before the plugin loads:
       highlights = {
         background = true,
         gutter = true,
+        blend_alpha = 0.6,
+        context = {
+          enabled = true,
+          lines = 25,
+        },
         treesitter = {
           enabled = true,
           max_lines = 500,
@@ -64,11 +70,30 @@ Configuration is done via `vim.g.diffs`. Set this before the plugin loads:
           enabled = false,
           max_lines = 200,
         },
+        intra = {
+          enabled = true,
+          algorithm = 'default',
+          max_lines = 500,
+        },
+        overrides = {},
       },
       fugitive = {
         horizontal = 'du',
         vertical = 'dU',
       },
+      conflict = {
+        enabled = true,
+        disable_diagnostics = true,
+        show_virtual_text = true,
+        keymaps = {
+          ours = 'doo',
+          theirs = 'dot',
+          both = 'dob',
+          none = 'don',
+          next = ']x',
+          prev = '[x',
+        },
+      },
     }
 <
                                                               *diffs.Config*
@@ -97,6 +122,10 @@ Configuration is done via `vim.g.diffs`. Set this before the plugin loads:
                              Fugitive status buffer keymap options.
                              See |diffs.FugitiveConfig| for fields.
 
+        {conflict}           (table, default: see below)
+                             Inline merge conflict resolution options.
+                             See |diffs.ConflictConfig| for fields.
+
                                                           *diffs.Highlights*
     Highlights table fields: ~
         {background}         (boolean, default: true)
@@ -108,6 +137,17 @@ Configuration is done via `vim.g.diffs`. Set this before the plugin loads:
                              Highlight line numbers with matching colors.
                              Only visible if line numbers are enabled.
 
+        {blend_alpha}        (number, default: 0.6)
+                             Alpha value for character-level blend intensity.
+                             Controls how strongly changed characters stand
+                             out from the line-level background. Must be
+                             between 0 and 1 (inclusive). Higher values
+                             produce more vivid character-level highlights.
+
+        {context}            (table, default: see below)
+                             Syntax parsing context options.
+                             See |diffs.ContextConfig| for fields.
+
         {treesitter}         (table, default: see below)
                              Treesitter highlighting options.
                              See |diffs.TreesitterConfig| for fields.
@@ -116,6 +156,31 @@ Configuration is done via `vim.g.diffs`. Set this before the plugin loads:
                              Vim syntax highlighting options (experimental).
                              See |diffs.VimConfig| for fields.
 
+        {intra}              (table, default: see below)
+                             Character-level (intra-line) diff highlighting.
+                             See |diffs.IntraConfig| for fields.
+
+        {overrides}          (table, default: {})
+                             Map of highlight group names to highlight
+                             definitions (see |nvim_set_hl()|). Applied
+                             after all computed groups without `default`,
+                             so overrides always win over both computed
+                             defaults and colorscheme definitions.
+
+                                                      *diffs.ContextConfig*
+    Context config fields: ~
+        {enabled}            (boolean, default: true)
+                             Read lines from disk before and after each hunk
+                             to provide surrounding syntax context. Improves
+                             accuracy at hunk boundaries where incomplete
+                             constructs (e.g., a function definition with no
+                             body) would otherwise confuse the parser.
+
+        {lines}              (integer, default: 25)
+                             Number of context lines to read in each
+                             direction. Lines are read with early exit —
+                             cost scales with this value, not file size.
+
                                                     *diffs.TreesitterConfig*
     Treesitter config fields: ~
         {enabled}            (boolean, default: true)
@@ -140,6 +205,26 @@ Configuration is done via `vim.g.diffs`. Set this before the plugin loads:
                              this many lines. Lower than the treesitter default
                              due to the per-character cost of |synID()|.
 
+                                                        *diffs.IntraConfig*
+    Intra config fields: ~
+        {enabled}            (boolean, default: true)
+                             Enable character-level diff highlighting within
+                             changed lines. When a line changes from `local x = 1`
+                             to `local x = 2`, only the `1`/`2` characters get
+                             an intense background overlay while the rest of the
+                             line keeps the softer line-level background.
+
+        {algorithm}          (string, default: 'default')
+                             Diff algorithm for character-level analysis.
+                             `'default'`: use |vim.diff()| with settings
+                             inherited from |'diffopt'| (`algorithm` and
+                             `linematch`). `'vscode'`: use libvscodediff FFI
+                             (falls back to default if not available).
+
+        {max_lines}          (integer, default: 500)
+                             Skip character-level highlighting for hunks larger
+                             than this many lines.
+
     Note: Header context (e.g., `@@ -10,3 +10,4 @@ func()`) is always
     highlighted with treesitter when a parser is available.
 
@@ -159,6 +244,9 @@ COMMANDS                                                      *diffs-commands*
     code language, plus diff header highlighting for `diff --git`, `---`,
     `+++`, and `@@` lines.
 
+    If a `diffs://` window already exists in the current tabpage, the new
+    diff replaces its buffer instead of creating another split.
+
     Parameters: ~
         {revision}  (string, optional) Git revision to diff against.
                     Defaults to HEAD.
@@ -176,6 +264,63 @@ COMMANDS                                                      *diffs-commands*
 :Ghdiff [revision]                                                  *:Ghdiff*
     Like |:Gdiff| but explicitly opens in a horizontal split.
 
+==============================================================================
+MAPPINGS                                                     *diffs-mappings*
+
+                                                        *<Plug>(diffs-gdiff)*
+<Plug>(diffs-gdiff)     Show unified diff against HEAD in a horizontal
+                        split. Equivalent to |:Gdiff| with no arguments.
+
+                                                       *<Plug>(diffs-gvdiff)*
+<Plug>(diffs-gvdiff)    Show unified diff against HEAD in a vertical
+                        split. Equivalent to |:Gvdiff| with no arguments.
+
+Example configuration: >lua
+    vim.keymap.set('n', '<leader>gd', '<Plug>(diffs-gdiff)')
+    vim.keymap.set('n', '<leader>gD', '<Plug>(diffs-gvdiff)')
+<
+
+                                              *<Plug>(diffs-conflict-ours)*
+<Plug>(diffs-conflict-ours)
+                        Accept current (ours) change. Replaces the
+                        conflict block with ours content.
+
+                                            *<Plug>(diffs-conflict-theirs)*
+<Plug>(diffs-conflict-theirs)
+                        Accept incoming (theirs) change. Replaces the
+                        conflict block with theirs content.
+
+                                              *<Plug>(diffs-conflict-both)*
+<Plug>(diffs-conflict-both)
+                        Accept both changes (ours then theirs).
+
+                                              *<Plug>(diffs-conflict-none)*
+<Plug>(diffs-conflict-none)
+                        Reject both changes (delete entire block).
+
+                                              *<Plug>(diffs-conflict-next)*
+<Plug>(diffs-conflict-next)
+                        Jump to next conflict marker. Wraps around.
+
+                                              *<Plug>(diffs-conflict-prev)*
+<Plug>(diffs-conflict-prev)
+                        Jump to previous conflict marker. Wraps around.
+
+Example configuration: >lua
+    vim.keymap.set('n', 'co', '<Plug>(diffs-conflict-ours)')
+    vim.keymap.set('n', 'ct', '<Plug>(diffs-conflict-theirs)')
+    vim.keymap.set('n', 'cb', '<Plug>(diffs-conflict-both)')
+    vim.keymap.set('n', 'cn', '<Plug>(diffs-conflict-none)')
+    vim.keymap.set('n', ']x', '<Plug>(diffs-conflict-next)')
+    vim.keymap.set('n', '[x', '<Plug>(diffs-conflict-prev)')
+<
+
+Diff buffer mappings: ~
+                                                              *diffs-q*
+    q               Close the diff window. Available in all `diffs://`
+                    buffers created by |:Gdiff|, |:Gvdiff|, |:Ghdiff|,
+                    or the fugitive status keymaps.
+
 ==============================================================================
 FUGITIVE STATUS KEYMAPS                                   *diffs-fugitive*
 
@@ -225,6 +370,94 @@ Configuration: ~
                              Keymap for unified diff in vertical split.
                              Set to `false` to disable.
 
+==============================================================================
+CONFLICT RESOLUTION                                          *diffs-conflict*
+
+diffs.nvim detects inline merge conflict markers (`<<<<<<<`/`=======`/
+`>>>>>>>`) in working files and provides highlighting and resolution keymaps.
+Both standard and diff3 (`|||||||`) formats are supported.
+
+Conflict regions are detected automatically on `BufReadPost` and re-scanned
+on `TextChanged`. When all conflicts in a buffer are resolved, highlighting
+is removed and diagnostics are re-enabled.
+
+Configuration: ~
+                                                      *diffs.ConflictConfig*
+>lua
+    vim.g.diffs = {
+      conflict = {
+        enabled = true,
+        disable_diagnostics = true,
+        show_virtual_text = true,
+        keymaps = {
+          ours = 'doo',
+          theirs = 'dot',
+          both = 'dob',
+          none = 'don',
+          next = ']x',
+          prev = '[x',
+        },
+      },
+    }
+<
+    Fields: ~
+        {enabled}            (boolean, default: true)
+                             Enable conflict marker detection and
+                             resolution. Set to `false` to disable
+                             entirely.
+
+        {disable_diagnostics} (boolean, default: true)
+                             Suppress LSP diagnostics on buffers with
+                             conflict markers. Markers produce syntax
+                             errors that clutter the diagnostic list.
+                             Diagnostics are re-enabled when all conflicts
+                             are resolved. Set `false` to leave
+                             diagnostics alone.
+
+        {show_virtual_text}  (boolean, default: true)
+                             Show virtual text labels (" current" and
+                             " incoming") at the end of `<<<<<<<` and
+                             `>>>>>>>` marker lines.
+
+        {keymaps}            (table, default: see above)
+                             Buffer-local keymaps for conflict resolution
+                             and navigation. Each value accepts a string
+                             (custom key) or `false` (disabled).
+
+                                                  *diffs.ConflictKeymaps*
+    Keymap fields: ~
+        {ours}               (string|false, default: 'doo')
+                             Accept current (ours) change.
+
+        {theirs}             (string|false, default: 'dot')
+                             Accept incoming (theirs) change.
+
+        {both}               (string|false, default: 'dob')
+                             Accept both changes (ours then theirs).
+
+        {none}               (string|false, default: 'don')
+                             Reject both changes (delete entire block).
+
+        {next}               (string|false, default: ']x')
+                             Jump to next conflict marker. Wraps around.
+
+        {prev}               (string|false, default: '[x')
+                             Jump to previous conflict marker. Wraps
+                             around.
+
+User events: ~
+                                                   *DiffsConflictResolved*
+    DiffsConflictResolved   Fired when the last conflict in a buffer is
+                            resolved. Useful for triggering custom actions
+                            (e.g., auto-staging the file). >lua
+                                vim.api.nvim_create_autocmd('User', {
+                                  pattern = 'DiffsConflictResolved',
+                                  callback = function()
+                                    print('all conflicts resolved!')
+                                  end,
+                                })
+<
+
 ==============================================================================
 API                                                                *diffs-api*
 
@@ -256,9 +489,11 @@ Summary / commit detail views: ~
    - Code is parsed with |vim.treesitter.get_string_parser()|
    - If no treesitter parser and `vim.enabled`: vim syntax fallback via
      scratch buffer and |synID()|
-   - Background extmarks (`DiffsAdd`/`DiffsDelete`) at priority 198
-   - `Normal` extmarks at priority 199 clear underlying diff foreground
+   - `Normal` extmarks at priority 198 clear underlying diff foreground
+   - Background extmarks (`DiffsAdd`/`DiffsDelete`) at priority 199
    - Syntax highlights are applied as extmarks at priority 200
+   - Character-level diff extmarks (`DiffsAddText`/`DiffsDeleteText`) at
+     priority 201 overlay changed characters with an intense background
    - Conceal extmarks hide diff prefixes when `hide_prefix` is enabled
 4. Re-highlighting occurs on `TextChanged` (debounced) and `Syntax` events
 
@@ -274,14 +509,15 @@ KNOWN LIMITATIONS                                       *diffs-limitations*
 
 Incomplete Syntax Context ~
                                                       *diffs-syntax-context*
-Treesitter parses each diff hunk in isolation without surrounding code
-context. When a hunk shows lines added to an existing block (e.g., adding a
-plugin inside `return { ... }`), the parser doesn't see the `return`
-statement and may produce incorrect or unusual highlighting.
+Treesitter parses each diff hunk in isolation. To provide surrounding code
+context, diffs.nvim reads lines from disk before and after each hunk
+(see |diffs.ContextConfig|, enabled by default). This resolves most boundary
+issues where incomplete constructs (e.g., a function definition at the edge
+of a hunk with no body) would confuse the parser.
 
-This is inherent to parsing code fragments. No diff tooling solves this
-problem without significant complexity—the parser simply doesn't have enough
-information to understand the full syntactic structure.
+Set `highlights.context.enabled = false` to disable context padding. In rare
+cases, context padding may not help if the relevant surrounding code is very
+far from the hunk boundaries.
 
 Syntax Highlighting Flash ~
                                                              *diffs-flash*
@@ -319,8 +555,9 @@ conflict:
       modifying line highlights may produce unexpected results.
 
   - git-conflict.nvim (akinsho/git-conflict.nvim)
-      Provides conflict marker highlighting that may overlap with
-      diffs.nvim's highlighting in conflict scenarios.
+      Provides conflict marker highlighting and resolution keymaps.
+      diffs.nvim now has built-in conflict resolution (see
+      |diffs-conflict|). Disable one or the other to avoid overlap.
 
 If you experience visual conflicts, try disabling the conflicting plugin's
 diff-related features.
@@ -328,9 +565,15 @@ diff-related features.
 ==============================================================================
 HIGHLIGHT GROUPS                                          *diffs-highlights*
 
-diffs.nvim defines custom highlight groups. Fugitive unified diff groups use
-`default = true`, so colorschemes can override them. Diff mode groups are
-always derived from the corresponding `Diff*` groups.
+diffs.nvim defines custom highlight groups. All groups use `default = true`,
+so colorschemes can override them by defining the group before the plugin
+loads.
+
+All derived groups are computed by alpha-blending a source color into the
+`Normal` background. Line-level groups blend at 40% alpha for a subtle tint;
+character-level groups blend at 60% for more contrast. Line-number groups
+combine both: background from the line-level blend, foreground from the
+character-level blend.
 
 Fugitive unified diff highlights: ~
                                                                   *DiffsAdd*
@@ -343,11 +586,54 @@ Fugitive unified diff highlights: ~
 
                                                                 *DiffsAddNr*
     DiffsAddNr          Line number for `+` lines. Foreground from
-                        `diffAdded`, background from `DiffsAdd`.
+                        `DiffsAddText`, background from `DiffsAdd`.
 
                                                              *DiffsDeleteNr*
     DiffsDeleteNr       Line number for `-` lines. Foreground from
-                        `diffRemoved`, background from `DiffsDelete`.
+                        `DiffsDeleteText`, background from `DiffsDelete`.
+
+                                                              *DiffsAddText*
+    DiffsAddText        Character-level background for changed characters
+                        within `+` lines. Derived by blending `diffAdded`
+                        foreground with `Normal` background at 60% alpha.
+                        Only sets `bg`, so treesitter foreground colors show
+                        through.
+
+                                                           *DiffsDeleteText*
+    DiffsDeleteText     Character-level background for changed characters
+                        within `-` lines. Derived by blending `diffRemoved`
+                        foreground with `Normal` background at 60% alpha.
+
+Conflict highlights: ~
+                                                        *DiffsConflictOurs*
+    DiffsConflictOurs   Background for "ours" (current) content lines.
+                        Derived by blending `DiffAdd` background with
+                        `Normal` at 40% alpha (green tint).
+
+                                                      *DiffsConflictTheirs*
+    DiffsConflictTheirs Background for "theirs" (incoming) content lines.
+                        Derived by blending `DiffChange` background with
+                        `Normal` at 40% alpha.
+
+                                                        *DiffsConflictBase*
+    DiffsConflictBase   Background for base (ancestor) content lines in
+                        diff3 conflicts. Derived by blending `DiffText`
+                        background with `Normal` at 30% alpha (muted).
+
+                                                      *DiffsConflictMarker*
+    DiffsConflictMarker Dimmed foreground with bold for `<<<<<<<`,
+                        `=======`, `>>>>>>>`, and `|||||||` marker lines.
+
+                                                      *DiffsConflictOursNr*
+    DiffsConflictOursNr Line number for "ours" content lines. Foreground
+                        from higher-alpha blend, background from line-level
+                        blend.
+
+                                                    *DiffsConflictTheirsNr*
+    DiffsConflictTheirsNr Line number for "theirs" content lines.
+
+                                                      *DiffsConflictBaseNr*
+    DiffsConflictBaseNr Line number for base content lines (diff3).
 
 Diff mode window highlights: ~
 These are used for |winhighlight| remapping in `&diff` windows.
@@ -373,6 +659,16 @@ To customize these in your colorscheme: >lua
     vim.api.nvim_set_hl(0, 'DiffsAdd', { bg = '#2e4a3a' })
     vim.api.nvim_set_hl(0, 'DiffsDiffDelete', { link = 'DiffDelete' })
 <
+Or via `highlights.overrides` in config: >lua
+    vim.g.diffs = {
+      highlights = {
+        overrides = {
+          DiffsAdd = { bg = '#2e4a3a' },
+          DiffsDiffDelete = { link = 'DiffDelete' },
+        },
+      },
+    }
+<
 
 ==============================================================================
 HEALTH CHECK                                                 *diffs-health*
@@ -382,6 +678,7 @@ Run |:checkhealth| diffs to verify your setup.
 Checks performed:
 - Neovim version >= 0.9.0
 - vim-fugitive is installed (optional)
+- libvscode_diff shared library is available (optional)
 
 ==============================================================================
 ACKNOWLEDGEMENTS                                     *diffs-acknowledgements*
@@ -389,7 +686,8 @@ ACKNOWLEDGEMENTS                                     *diffs-acknowledgements*
 - vim-fugitive (https://github.com/tpope/vim-fugitive)
 - codediff.nvim (https://github.com/esmuellert/codediff.nvim)
 - diffview.nvim (https://github.com/sindrets/diffview.nvim)
-- @phanen (https://github.com/phanen) - diff header highlighting
+- @phanen (https://github.com/phanen) - diff header highlighting,
+  treesitter injection support
 
 ==============================================================================
  vim:tw=78:ts=8:ft=help:norl:

lua/diffs/commands.lua

@@ -3,6 +3,27 @@ local M = {}
 local git = require('diffs.git')
 local dbg = require('diffs.log').dbg
 
+---@return integer?
+function M.find_diffs_window()
+  local tabpage = vim.api.nvim_get_current_tabpage()
+  for _, win in ipairs(vim.api.nvim_tabpage_list_wins(tabpage)) do
+    if vim.api.nvim_win_is_valid(win) then
+      local buf = vim.api.nvim_win_get_buf(win)
+      local name = vim.api.nvim_buf_get_name(buf)
+      if name:match('^diffs://') then
+        return win
+      end
+    end
+  end
+  return nil
+end
+
+---@param bufnr integer
+function M.setup_diff_buf(bufnr)
+  vim.diagnostic.enable(false, { bufnr = bufnr })
+  vim.keymap.set('n', 'q', '<cmd>close<CR>', { buffer = bufnr })
+end
+
 ---@param diff_lines string[]
 ---@param hunk_position { hunk_header: string, offset: integer }
 ---@return integer?
@@ -86,8 +107,9 @@ function M.gdiff(revision, vertical)
 
   local diff_buf = vim.api.nvim_create_buf(false, true)
   vim.api.nvim_buf_set_lines(diff_buf, 0, -1, false, diff_lines)
-  vim.api.nvim_set_option_value('buftype', 'nofile', { buf = diff_buf })
-  vim.api.nvim_set_option_value('bufhidden', 'wipe', { buf = diff_buf })
+  vim.api.nvim_set_option_value('buftype', 'nowrite', { buf = diff_buf })
+  vim.api.nvim_set_option_value('bufhidden', 'delete', { buf = diff_buf })
+  vim.api.nvim_set_option_value('swapfile', false, { buf = diff_buf })
   vim.api.nvim_set_option_value('modifiable', false, { buf = diff_buf })
   vim.api.nvim_set_option_value('filetype', 'diff', { buf = diff_buf })
   vim.api.nvim_buf_set_name(diff_buf, 'diffs://' .. revision .. ':' .. rel_path)
@@ -95,9 +117,16 @@ function M.gdiff(revision, vertical)
     vim.api.nvim_buf_set_var(diff_buf, 'diffs_repo_root', repo_root)
   end
 
-  vim.cmd(vertical and 'vsplit' or 'split')
-  vim.api.nvim_win_set_buf(0, diff_buf)
+  local existing_win = M.find_diffs_window()
+  if existing_win then
+    vim.api.nvim_set_current_win(existing_win)
+    vim.api.nvim_win_set_buf(existing_win, diff_buf)
+  else
+    vim.cmd(vertical and 'vsplit' or 'split')
+    vim.api.nvim_win_set_buf(0, diff_buf)
+  end
 
+  M.setup_diff_buf(diff_buf)
   dbg('opened diff buffer %d for %s against %s', diff_buf, rel_path, revision)
 
   vim.schedule(function()
@@ -176,17 +205,27 @@ function M.gdiff_file(filepath, opts)
 
   local diff_buf = vim.api.nvim_create_buf(false, true)
   vim.api.nvim_buf_set_lines(diff_buf, 0, -1, false, diff_lines)
-  vim.api.nvim_set_option_value('buftype', 'nofile', { buf = diff_buf })
-  vim.api.nvim_set_option_value('bufhidden', 'wipe', { buf = diff_buf })
+  vim.api.nvim_set_option_value('buftype', 'nowrite', { buf = diff_buf })
+  vim.api.nvim_set_option_value('bufhidden', 'delete', { buf = diff_buf })
+  vim.api.nvim_set_option_value('swapfile', false, { buf = diff_buf })
   vim.api.nvim_set_option_value('modifiable', false, { buf = diff_buf })
   vim.api.nvim_set_option_value('filetype', 'diff', { buf = diff_buf })
   vim.api.nvim_buf_set_name(diff_buf, 'diffs://' .. diff_label .. ':' .. rel_path)
   if repo_root then
     vim.api.nvim_buf_set_var(diff_buf, 'diffs_repo_root', repo_root)
   end
+  if old_rel_path ~= rel_path then
+    vim.api.nvim_buf_set_var(diff_buf, 'diffs_old_filepath', old_rel_path)
+  end
 
-  vim.cmd(opts.vertical and 'vsplit' or 'split')
-  vim.api.nvim_win_set_buf(0, diff_buf)
+  local existing_win = M.find_diffs_window()
+  if existing_win then
+    vim.api.nvim_set_current_win(existing_win)
+    vim.api.nvim_win_set_buf(existing_win, diff_buf)
+  else
+    vim.cmd(opts.vertical and 'vsplit' or 'split')
+    vim.api.nvim_win_set_buf(0, diff_buf)
+  end
 
   if opts.hunk_position then
     local target_line = M.find_hunk_line(diff_lines, opts.hunk_position)
@@ -196,6 +235,7 @@ function M.gdiff_file(filepath, opts)
     end
   end
 
+  M.setup_diff_buf(diff_buf)
   dbg('opened diff buffer %d for %s (%s)', diff_buf, rel_path, diff_label)
 
   vim.schedule(function()
@@ -231,16 +271,24 @@ function M.gdiff_section(repo_root, opts)
   local diff_label = opts.staged and 'staged' or 'unstaged'
   local diff_buf = vim.api.nvim_create_buf(false, true)
   vim.api.nvim_buf_set_lines(diff_buf, 0, -1, false, result)
-  vim.api.nvim_set_option_value('buftype', 'nofile', { buf = diff_buf })
-  vim.api.nvim_set_option_value('bufhidden', 'wipe', { buf = diff_buf })
+  vim.api.nvim_set_option_value('buftype', 'nowrite', { buf = diff_buf })
+  vim.api.nvim_set_option_value('bufhidden', 'delete', { buf = diff_buf })
+  vim.api.nvim_set_option_value('swapfile', false, { buf = diff_buf })
   vim.api.nvim_set_option_value('modifiable', false, { buf = diff_buf })
   vim.api.nvim_set_option_value('filetype', 'diff', { buf = diff_buf })
   vim.api.nvim_buf_set_name(diff_buf, 'diffs://' .. diff_label .. ':all')
   vim.api.nvim_buf_set_var(diff_buf, 'diffs_repo_root', repo_root)
 
-  vim.cmd(opts.vertical and 'vsplit' or 'split')
-  vim.api.nvim_win_set_buf(0, diff_buf)
+  local existing_win = M.find_diffs_window()
+  if existing_win then
+    vim.api.nvim_set_current_win(existing_win)
+    vim.api.nvim_win_set_buf(existing_win, diff_buf)
+  else
+    vim.cmd(opts.vertical and 'vsplit' or 'split')
+    vim.api.nvim_win_set_buf(0, diff_buf)
+  end
 
+  M.setup_diff_buf(diff_buf)
   dbg('opened section diff buffer %d (%s)', diff_buf, diff_label)
 
   vim.schedule(function()
@@ -248,6 +296,77 @@ function M.gdiff_section(repo_root, opts)
   end)
 end
 
+---@param bufnr integer
+function M.read_buffer(bufnr)
+  local name = vim.api.nvim_buf_get_name(bufnr)
+  local url_body = name:match('^diffs://(.+)$')
+  if not url_body then
+    return
+  end
+
+  local label, path = url_body:match('^([^:]+):(.+)$')
+  if not label or not path then
+    return
+  end
+
+  local ok, repo_root = pcall(vim.api.nvim_buf_get_var, bufnr, 'diffs_repo_root')
+  if not ok or not repo_root then
+    return
+  end
+
+  local diff_lines
+
+  if path == 'all' then
+    local cmd = { 'git', '-C', repo_root, 'diff', '--no-ext-diff', '--no-color' }
+    if label == 'staged' then
+      table.insert(cmd, '--cached')
+    end
+    diff_lines = vim.fn.systemlist(cmd)
+    if vim.v.shell_error ~= 0 then
+      diff_lines = {}
+    end
+  else
+    local abs_path = repo_root .. '/' .. path
+
+    local old_ok, old_rel_path = pcall(vim.api.nvim_buf_get_var, bufnr, 'diffs_old_filepath')
+    local old_abs_path = old_ok and old_rel_path and (repo_root .. '/' .. old_rel_path) or abs_path
+    local old_name = old_ok and old_rel_path or path
+
+    local old_lines, new_lines
+
+    if label == 'untracked' then
+      old_lines = {}
+      new_lines = git.get_working_content(abs_path) or {}
+    elseif label == 'staged' then
+      old_lines = git.get_file_content('HEAD', old_abs_path) or {}
+      new_lines = git.get_index_content(abs_path) or {}
+    elseif label == 'unstaged' then
+      old_lines = git.get_index_content(old_abs_path)
+      if not old_lines then
+        old_lines = git.get_file_content('HEAD', old_abs_path) or {}
+      end
+      new_lines = git.get_working_content(abs_path) or {}
+    else
+      old_lines = git.get_file_content(label, abs_path) or {}
+      new_lines = git.get_working_content(abs_path) or {}
+    end
+
+    diff_lines = generate_unified_diff(old_lines, new_lines, old_name, path)
+  end
+
+  vim.api.nvim_set_option_value('modifiable', true, { buf = bufnr })
+  vim.api.nvim_buf_set_lines(bufnr, 0, -1, false, diff_lines)
+  vim.api.nvim_set_option_value('modifiable', false, { buf = bufnr })
+  vim.api.nvim_set_option_value('buftype', 'nowrite', { buf = bufnr })
+  vim.api.nvim_set_option_value('bufhidden', 'delete', { buf = bufnr })
+  vim.api.nvim_set_option_value('swapfile', false, { buf = bufnr })
+  vim.api.nvim_set_option_value('filetype', 'diff', { buf = bufnr })
+
+  dbg('reloaded diff buffer %d (%s:%s)', bufnr, label, path)
+
+  require('diffs').attach(bufnr)
+end
+
 function M.setup()
   vim.api.nvim_create_user_command('Gdiff', function(opts)
     M.gdiff(opts.args ~= '' and opts.args or nil, false)

lua/diffs/conflict.lua

@@ -0,0 +1,438 @@
+---@class diffs.ConflictRegion
+---@field marker_ours integer
+---@field ours_start integer
+---@field ours_end integer
+---@field marker_base integer?
+---@field base_start integer?
+---@field base_end integer?
+---@field marker_sep integer
+---@field theirs_start integer
+---@field theirs_end integer
+---@field marker_theirs integer
+
+local M = {}
+
+local ns = vim.api.nvim_create_namespace('diffs-conflict')
+
+---@type table<integer, true>
+local attached_buffers = {}
+
+---@type table<integer, boolean>
+local diagnostics_suppressed = {}
+
+local PRIORITY_LINE_BG = 200
+
+---@param lines string[]
+---@return diffs.ConflictRegion[]
+function M.parse(lines)
+  local regions = {}
+  local state = 'idle'
+  ---@type table?
+  local current = nil
+
+  for i, line in ipairs(lines) do
+    local idx = i - 1
+
+    if state == 'idle' then
+      if line:match('^<<<<<<<') then
+        current = { marker_ours = idx, ours_start = idx + 1 }
+        state = 'in_ours'
+      end
+    elseif state == 'in_ours' then
+      if line:match('^|||||||') then
+        current.ours_end = idx
+        current.marker_base = idx
+        current.base_start = idx + 1
+        state = 'in_base'
+      elseif line:match('^=======') then
+        current.ours_end = idx
+        current.marker_sep = idx
+        current.theirs_start = idx + 1
+        state = 'in_theirs'
+      elseif line:match('^<<<<<<<') then
+        current = { marker_ours = idx, ours_start = idx + 1 }
+      elseif line:match('^>>>>>>>') then
+        current = nil
+        state = 'idle'
+      end
+    elseif state == 'in_base' then
+      if line:match('^=======') then
+        current.base_end = idx
+        current.marker_sep = idx
+        current.theirs_start = idx + 1
+        state = 'in_theirs'
+      elseif line:match('^<<<<<<<') then
+        current = { marker_ours = idx, ours_start = idx + 1 }
+        state = 'in_ours'
+      elseif line:match('^>>>>>>>') then
+        current = nil
+        state = 'idle'
+      end
+    elseif state == 'in_theirs' then
+      if line:match('^>>>>>>>') then
+        current.theirs_end = idx
+        current.marker_theirs = idx
+        table.insert(regions, current)
+        current = nil
+        state = 'idle'
+      elseif line:match('^<<<<<<<') then
+        current = { marker_ours = idx, ours_start = idx + 1 }
+        state = 'in_ours'
+      end
+    end
+  end
+
+  return regions
+end
+
+---@param bufnr integer
+---@return diffs.ConflictRegion[]
+local function parse_buffer(bufnr)
+  local lines = vim.api.nvim_buf_get_lines(bufnr, 0, -1, false)
+  return M.parse(lines)
+end
+
+---@param bufnr integer
+---@param regions diffs.ConflictRegion[]
+---@param config diffs.ConflictConfig
+local function apply_highlights(bufnr, regions, config)
+  vim.api.nvim_buf_clear_namespace(bufnr, ns, 0, -1)
+
+  for _, region in ipairs(regions) do
+    pcall(vim.api.nvim_buf_set_extmark, bufnr, ns, region.marker_ours, 0, {
+      end_row = region.marker_ours + 1,
+      hl_group = 'DiffsConflictMarker',
+      hl_eol = true,
+      priority = PRIORITY_LINE_BG,
+    })
+
+    if config.show_virtual_text then
+      pcall(vim.api.nvim_buf_set_extmark, bufnr, ns, region.marker_ours, 0, {
+        virt_text = { { ' (current)', 'DiffsConflictMarker' } },
+        virt_text_pos = 'eol',
+      })
+    end
+
+    for line = region.ours_start, region.ours_end - 1 do
+      pcall(vim.api.nvim_buf_set_extmark, bufnr, ns, line, 0, {
+        end_row = line + 1,
+        hl_group = 'DiffsConflictOurs',
+        hl_eol = true,
+        priority = PRIORITY_LINE_BG,
+      })
+      pcall(vim.api.nvim_buf_set_extmark, bufnr, ns, line, 0, {
+        number_hl_group = 'DiffsConflictOursNr',
+        priority = PRIORITY_LINE_BG,
+      })
+    end
+
+    if region.marker_base then
+      pcall(vim.api.nvim_buf_set_extmark, bufnr, ns, region.marker_base, 0, {
+        end_row = region.marker_base + 1,
+        hl_group = 'DiffsConflictMarker',
+        hl_eol = true,
+        priority = PRIORITY_LINE_BG,
+      })
+
+      for line = region.base_start, region.base_end - 1 do
+        pcall(vim.api.nvim_buf_set_extmark, bufnr, ns, line, 0, {
+          end_row = line + 1,
+          hl_group = 'DiffsConflictBase',
+          hl_eol = true,
+          priority = PRIORITY_LINE_BG,
+        })
+        pcall(vim.api.nvim_buf_set_extmark, bufnr, ns, line, 0, {
+          number_hl_group = 'DiffsConflictBaseNr',
+          priority = PRIORITY_LINE_BG,
+        })
+      end
+    end
+
+    pcall(vim.api.nvim_buf_set_extmark, bufnr, ns, region.marker_sep, 0, {
+      end_row = region.marker_sep + 1,
+      hl_group = 'DiffsConflictMarker',
+      hl_eol = true,
+      priority = PRIORITY_LINE_BG,
+    })
+
+    for line = region.theirs_start, region.theirs_end - 1 do
+      pcall(vim.api.nvim_buf_set_extmark, bufnr, ns, line, 0, {
+        end_row = line + 1,
+        hl_group = 'DiffsConflictTheirs',
+        hl_eol = true,
+        priority = PRIORITY_LINE_BG,
+      })
+      pcall(vim.api.nvim_buf_set_extmark, bufnr, ns, line, 0, {
+        number_hl_group = 'DiffsConflictTheirsNr',
+        priority = PRIORITY_LINE_BG,
+      })
+    end
+
+    pcall(vim.api.nvim_buf_set_extmark, bufnr, ns, region.marker_theirs, 0, {
+      end_row = region.marker_theirs + 1,
+      hl_group = 'DiffsConflictMarker',
+      hl_eol = true,
+      priority = PRIORITY_LINE_BG,
+    })
+
+    if config.show_virtual_text then
+      pcall(vim.api.nvim_buf_set_extmark, bufnr, ns, region.marker_theirs, 0, {
+        virt_text = { { ' (incoming)', 'DiffsConflictMarker' } },
+        virt_text_pos = 'eol',
+      })
+    end
+  end
+end
+
+---@param cursor_line integer
+---@param regions diffs.ConflictRegion[]
+---@return diffs.ConflictRegion?
+local function find_conflict_at_cursor(cursor_line, regions)
+  for _, region in ipairs(regions) do
+    if cursor_line >= region.marker_ours and cursor_line <= region.marker_theirs then
+      return region
+    end
+  end
+  return nil
+end
+
+---@param bufnr integer
+---@param region diffs.ConflictRegion
+---@param replacement string[]
+local function replace_region(bufnr, region, replacement)
+  vim.api.nvim_buf_set_lines(
+    bufnr,
+    region.marker_ours,
+    region.marker_theirs + 1,
+    false,
+    replacement
+  )
+end
+
+---@param bufnr integer
+---@param config diffs.ConflictConfig
+local function refresh(bufnr, config)
+  local regions = parse_buffer(bufnr)
+  if #regions == 0 then
+    vim.api.nvim_buf_clear_namespace(bufnr, ns, 0, -1)
+    if diagnostics_suppressed[bufnr] then
+      pcall(vim.diagnostic.reset, nil, bufnr)
+      pcall(vim.diagnostic.enable, true, { bufnr = bufnr })
+      diagnostics_suppressed[bufnr] = nil
+    end
+    vim.api.nvim_exec_autocmds('User', { pattern = 'DiffsConflictResolved' })
+    return
+  end
+  apply_highlights(bufnr, regions, config)
+  if config.disable_diagnostics and not diagnostics_suppressed[bufnr] then
+    pcall(vim.diagnostic.enable, false, { bufnr = bufnr })
+    diagnostics_suppressed[bufnr] = true
+  end
+end
+
+---@param bufnr integer
+---@param config diffs.ConflictConfig
+function M.resolve_ours(bufnr, config)
+  if not vim.api.nvim_get_option_value('modifiable', { buf = bufnr }) then
+    vim.notify('[diffs.nvim]: buffer is not modifiable', vim.log.levels.WARN)
+    return
+  end
+  local regions = parse_buffer(bufnr)
+  local cursor = vim.api.nvim_win_get_cursor(0)
+  local region = find_conflict_at_cursor(cursor[1] - 1, regions)
+  if not region then
+    return
+  end
+  local lines = vim.api.nvim_buf_get_lines(bufnr, region.ours_start, region.ours_end, false)
+  replace_region(bufnr, region, lines)
+  refresh(bufnr, config)
+end
+
+---@param bufnr integer
+---@param config diffs.ConflictConfig
+function M.resolve_theirs(bufnr, config)
+  if not vim.api.nvim_get_option_value('modifiable', { buf = bufnr }) then
+    vim.notify('[diffs.nvim]: buffer is not modifiable', vim.log.levels.WARN)
+    return
+  end
+  local regions = parse_buffer(bufnr)
+  local cursor = vim.api.nvim_win_get_cursor(0)
+  local region = find_conflict_at_cursor(cursor[1] - 1, regions)
+  if not region then
+    return
+  end
+  local lines = vim.api.nvim_buf_get_lines(bufnr, region.theirs_start, region.theirs_end, false)
+  replace_region(bufnr, region, lines)
+  refresh(bufnr, config)
+end
+
+---@param bufnr integer
+---@param config diffs.ConflictConfig
+function M.resolve_both(bufnr, config)
+  if not vim.api.nvim_get_option_value('modifiable', { buf = bufnr }) then
+    vim.notify('[diffs.nvim]: buffer is not modifiable', vim.log.levels.WARN)
+    return
+  end
+  local regions = parse_buffer(bufnr)
+  local cursor = vim.api.nvim_win_get_cursor(0)
+  local region = find_conflict_at_cursor(cursor[1] - 1, regions)
+  if not region then
+    return
+  end
+  local ours = vim.api.nvim_buf_get_lines(bufnr, region.ours_start, region.ours_end, false)
+  local theirs = vim.api.nvim_buf_get_lines(bufnr, region.theirs_start, region.theirs_end, false)
+  local combined = {}
+  for _, l in ipairs(ours) do
+    table.insert(combined, l)
+  end
+  for _, l in ipairs(theirs) do
+    table.insert(combined, l)
+  end
+  replace_region(bufnr, region, combined)
+  refresh(bufnr, config)
+end
+
+---@param bufnr integer
+---@param config diffs.ConflictConfig
+function M.resolve_none(bufnr, config)
+  if not vim.api.nvim_get_option_value('modifiable', { buf = bufnr }) then
+    vim.notify('[diffs.nvim]: buffer is not modifiable', vim.log.levels.WARN)
+    return
+  end
+  local regions = parse_buffer(bufnr)
+  local cursor = vim.api.nvim_win_get_cursor(0)
+  local region = find_conflict_at_cursor(cursor[1] - 1, regions)
+  if not region then
+    return
+  end
+  replace_region(bufnr, region, {})
+  refresh(bufnr, config)
+end
+
+---@param bufnr integer
+function M.goto_next(bufnr)
+  local regions = parse_buffer(bufnr)
+  if #regions == 0 then
+    return
+  end
+  local cursor = vim.api.nvim_win_get_cursor(0)
+  local cursor_line = cursor[1] - 1
+  for _, region in ipairs(regions) do
+    if region.marker_ours > cursor_line then
+      vim.api.nvim_win_set_cursor(0, { region.marker_ours + 1, 0 })
+      return
+    end
+  end
+  vim.api.nvim_win_set_cursor(0, { regions[1].marker_ours + 1, 0 })
+end
+
+---@param bufnr integer
+function M.goto_prev(bufnr)
+  local regions = parse_buffer(bufnr)
+  if #regions == 0 then
+    return
+  end
+  local cursor = vim.api.nvim_win_get_cursor(0)
+  local cursor_line = cursor[1] - 1
+  for i = #regions, 1, -1 do
+    if regions[i].marker_ours < cursor_line then
+      vim.api.nvim_win_set_cursor(0, { regions[i].marker_ours + 1, 0 })
+      return
+    end
+  end
+  vim.api.nvim_win_set_cursor(0, { regions[#regions].marker_ours + 1, 0 })
+end
+
+---@param bufnr integer
+---@param config diffs.ConflictConfig
+local function setup_keymaps(bufnr, config)
+  local km = config.keymaps
+
+  local maps = {
+    { km.ours, '<Plug>(diffs-conflict-ours)' },
+    { km.theirs, '<Plug>(diffs-conflict-theirs)' },
+    { km.both, '<Plug>(diffs-conflict-both)' },
+    { km.none, '<Plug>(diffs-conflict-none)' },
+    { km.next, '<Plug>(diffs-conflict-next)' },
+    { km.prev, '<Plug>(diffs-conflict-prev)' },
+  }
+
+  for _, map in ipairs(maps) do
+    if map[1] then
+      vim.keymap.set('n', map[1], map[2], { buffer = bufnr })
+    end
+  end
+end
+
+---@param bufnr integer
+function M.detach(bufnr)
+  vim.api.nvim_buf_clear_namespace(bufnr, ns, 0, -1)
+  attached_buffers[bufnr] = nil
+
+  if diagnostics_suppressed[bufnr] then
+    pcall(vim.diagnostic.reset, nil, bufnr)
+    pcall(vim.diagnostic.enable, true, { bufnr = bufnr })
+    diagnostics_suppressed[bufnr] = nil
+  end
+end
+
+---@param bufnr integer
+---@param config diffs.ConflictConfig
+function M.attach(bufnr, config)
+  if attached_buffers[bufnr] then
+    return
+  end
+
+  local buftype = vim.api.nvim_get_option_value('buftype', { buf = bufnr })
+  if buftype ~= '' then
+    return
+  end
+
+  local lines = vim.api.nvim_buf_get_lines(bufnr, 0, -1, false)
+  local has_marker = false
+  for _, line in ipairs(lines) do
+    if line:match('^<<<<<<<') then
+      has_marker = true
+      break
+    end
+  end
+  if not has_marker then
+    return
+  end
+
+  attached_buffers[bufnr] = true
+
+  local regions = M.parse(lines)
+  apply_highlights(bufnr, regions, config)
+  setup_keymaps(bufnr, config)
+
+  if config.disable_diagnostics then
+    pcall(vim.diagnostic.enable, false, { bufnr = bufnr })
+    diagnostics_suppressed[bufnr] = true
+  end
+
+  vim.api.nvim_create_autocmd({ 'TextChanged', 'TextChangedI' }, {
+    buffer = bufnr,
+    callback = function()
+      if not attached_buffers[bufnr] then
+        return true
+      end
+      refresh(bufnr, config)
+    end,
+  })
+
+  vim.api.nvim_create_autocmd('BufWipeout', {
+    buffer = bufnr,
+    callback = function()
+      attached_buffers[bufnr] = nil
+      diagnostics_suppressed[bufnr] = nil
+    end,
+  })
+end
+
+---@return integer
+function M.get_namespace()
+  return ns
+end
+
+return M

lua/diffs/debug.lua

@@ -0,0 +1,70 @@
+local M = {}
+
+local ns = vim.api.nvim_create_namespace('diffs')
+
+function M.dump()
+  local bufnr = vim.api.nvim_get_current_buf()
+  local marks = vim.api.nvim_buf_get_extmarks(bufnr, ns, 0, -1, { details = true })
+  local lines = vim.api.nvim_buf_get_lines(bufnr, 0, -1, false)
+
+  local by_line = {}
+  for _, mark in ipairs(marks) do
+    local id, row, col, details = mark[1], mark[2], mark[3], mark[4]
+    local entry = {
+      id = id,
+      row = row,
+      col = col,
+      end_row = details.end_row,
+      end_col = details.end_col,
+      hl_group = details.hl_group,
+      priority = details.priority,
+      hl_eol = details.hl_eol,
+      line_hl_group = details.line_hl_group,
+      number_hl_group = details.number_hl_group,
+      virt_text = details.virt_text,
+    }
+    local key = tostring(row)
+    if not by_line[key] then
+      by_line[key] = { text = lines[row + 1] or '', marks = {} }
+    end
+    table.insert(by_line[key].marks, entry)
+  end
+
+  local all_ns_marks = vim.api.nvim_buf_get_extmarks(bufnr, -1, 0, -1, { details = true })
+  local non_diffs = {}
+  for _, mark in ipairs(all_ns_marks) do
+    local details = mark[4]
+    if details.ns_id ~= ns then
+      table.insert(non_diffs, {
+        ns_id = details.ns_id,
+        row = mark[2],
+        col = mark[3],
+        end_row = details.end_row,
+        end_col = details.end_col,
+        hl_group = details.hl_group,
+        priority = details.priority,
+      })
+    end
+  end
+
+  local result = {
+    bufnr = bufnr,
+    buf_name = vim.api.nvim_buf_get_name(bufnr),
+    ns_id = ns,
+    total_diffs_marks = #marks,
+    total_all_marks = #all_ns_marks,
+    non_diffs_marks = non_diffs,
+    lines = by_line,
+  }
+
+  local state_dir = vim.fn.stdpath('state')
+  local path = state_dir .. '/diffs_debug.json'
+  local f = io.open(path, 'w')
+  if f then
+    f:write(vim.json.encode(result))
+    f:close()
+    vim.notify('[diffs.nvim] debug dump: ' .. path, vim.log.levels.INFO)
+  end
+end
+
+return M

lua/diffs/diff.lua

@@ -0,0 +1,401 @@
+---@class diffs.CharSpan
+---@field line integer
+---@field col_start integer
+---@field col_end integer
+
+---@class diffs.IntraChanges
+---@field add_spans diffs.CharSpan[]
+---@field del_spans diffs.CharSpan[]
+
+---@class diffs.ChangeGroup
+---@field del_lines {idx: integer, text: string}[]
+---@field add_lines {idx: integer, text: string}[]
+
+---@class diffs.DiffOpts
+---@field algorithm? string
+---@field linematch? integer
+
+local M = {}
+
+local dbg = require('diffs.log').dbg
+
+---@param hunk_lines string[]
+---@return diffs.ChangeGroup[]
+function M.extract_change_groups(hunk_lines)
+  ---@type diffs.ChangeGroup[]
+  local groups = {}
+  ---@type {idx: integer, text: string}[]
+  local del_buf = {}
+  ---@type {idx: integer, text: string}[]
+  local add_buf = {}
+
+  ---@type boolean
+  local in_del = false
+
+  for i, line in ipairs(hunk_lines) do
+    local prefix = line:sub(1, 1)
+    if prefix == '-' then
+      if not in_del and #add_buf > 0 then
+        if #del_buf > 0 then
+          table.insert(groups, { del_lines = del_buf, add_lines = add_buf })
+        end
+        del_buf = {}
+        add_buf = {}
+      end
+      in_del = true
+      table.insert(del_buf, { idx = i, text = line:sub(2) })
+    elseif prefix == '+' then
+      in_del = false
+      table.insert(add_buf, { idx = i, text = line:sub(2) })
+    else
+      if #del_buf > 0 and #add_buf > 0 then
+        table.insert(groups, { del_lines = del_buf, add_lines = add_buf })
+      end
+      del_buf = {}
+      add_buf = {}
+      in_del = false
+    end
+  end
+
+  if #del_buf > 0 and #add_buf > 0 then
+    table.insert(groups, { del_lines = del_buf, add_lines = add_buf })
+  end
+
+  return groups
+end
+
+---@return diffs.DiffOpts
+local function parse_diffopt()
+  local opts = {}
+  for _, item in ipairs(vim.split(vim.o.diffopt, ',')) do
+    local key, val = item:match('^(%w+):(.+)$')
+    if key == 'algorithm' then
+      opts.algorithm = val
+    elseif key == 'linematch' then
+      opts.linematch = tonumber(val)
+    end
+  end
+  return opts
+end
+
+---@param old_text string
+---@param new_text string
+---@param diff_opts? diffs.DiffOpts
+---@return {old_start: integer, old_count: integer, new_start: integer, new_count: integer}[]
+local function byte_diff(old_text, new_text, diff_opts)
+  local vim_opts = { result_type = 'indices' }
+  if diff_opts then
+    if diff_opts.algorithm then
+      vim_opts.algorithm = diff_opts.algorithm
+    end
+    if diff_opts.linematch then
+      vim_opts.linematch = diff_opts.linematch
+    end
+  end
+  local ok, result = pcall(vim.diff, old_text, new_text, vim_opts)
+  if not ok or not result then
+    return {}
+  end
+  ---@type {old_start: integer, old_count: integer, new_start: integer, new_count: integer}[]
+  local hunks = {}
+  for _, h in ipairs(result) do
+    table.insert(hunks, {
+      old_start = h[1],
+      old_count = h[2],
+      new_start = h[3],
+      new_count = h[4],
+    })
+  end
+  return hunks
+end
+
+---@param s string
+---@return string[]
+local function split_bytes(s)
+  local bytes = {}
+  for i = 1, #s do
+    table.insert(bytes, s:sub(i, i))
+  end
+  return bytes
+end
+
+---@param old_line string
+---@param new_line string
+---@param del_idx integer
+---@param add_idx integer
+---@param diff_opts? diffs.DiffOpts
+---@return diffs.CharSpan[], diffs.CharSpan[]
+local function char_diff_pair(old_line, new_line, del_idx, add_idx, diff_opts)
+  ---@type diffs.CharSpan[]
+  local del_spans = {}
+  ---@type diffs.CharSpan[]
+  local add_spans = {}
+
+  local old_bytes = split_bytes(old_line)
+  local new_bytes = split_bytes(new_line)
+
+  local old_text = table.concat(old_bytes, '\n') .. '\n'
+  local new_text = table.concat(new_bytes, '\n') .. '\n'
+
+  local char_opts = diff_opts
+  if diff_opts and diff_opts.linematch then
+    char_opts = { algorithm = diff_opts.algorithm }
+  end
+
+  local char_hunks = byte_diff(old_text, new_text, char_opts)
+
+  for _, ch in ipairs(char_hunks) do
+    if ch.old_count > 0 then
+      table.insert(del_spans, {
+        line = del_idx,
+        col_start = ch.old_start,
+        col_end = ch.old_start + ch.old_count,
+      })
+    end
+
+    if ch.new_count > 0 then
+      table.insert(add_spans, {
+        line = add_idx,
+        col_start = ch.new_start,
+        col_end = ch.new_start + ch.new_count,
+      })
+    end
+  end
+
+  return del_spans, add_spans
+end
+
+---@param group diffs.ChangeGroup
+---@param diff_opts? diffs.DiffOpts
+---@return diffs.CharSpan[], diffs.CharSpan[]
+local function diff_group_native(group, diff_opts)
+  ---@type diffs.CharSpan[]
+  local all_del = {}
+  ---@type diffs.CharSpan[]
+  local all_add = {}
+
+  local del_count = #group.del_lines
+  local add_count = #group.add_lines
+
+  if del_count == 1 and add_count == 1 then
+    local ds, as = char_diff_pair(
+      group.del_lines[1].text,
+      group.add_lines[1].text,
+      group.del_lines[1].idx,
+      group.add_lines[1].idx,
+      diff_opts
+    )
+    vim.list_extend(all_del, ds)
+    vim.list_extend(all_add, as)
+    return all_del, all_add
+  end
+
+  local old_texts = {}
+  for _, l in ipairs(group.del_lines) do
+    table.insert(old_texts, l.text)
+  end
+  local new_texts = {}
+  for _, l in ipairs(group.add_lines) do
+    table.insert(new_texts, l.text)
+  end
+
+  local old_block = table.concat(old_texts, '\n') .. '\n'
+  local new_block = table.concat(new_texts, '\n') .. '\n'
+
+  local line_hunks = byte_diff(old_block, new_block, diff_opts)
+
+  ---@type table<integer, integer>
+  local old_to_new = {}
+  for _, lh in ipairs(line_hunks) do
+    if lh.old_count == lh.new_count then
+      for k = 0, lh.old_count - 1 do
+        old_to_new[lh.old_start + k] = lh.new_start + k
+      end
+    end
+  end
+
+  for old_i, new_i in pairs(old_to_new) do
+    if group.del_lines[old_i] and group.add_lines[new_i] then
+      local ds, as = char_diff_pair(
+        group.del_lines[old_i].text,
+        group.add_lines[new_i].text,
+        group.del_lines[old_i].idx,
+        group.add_lines[new_i].idx,
+        diff_opts
+      )
+      vim.list_extend(all_del, ds)
+      vim.list_extend(all_add, as)
+    end
+  end
+
+  for _, lh in ipairs(line_hunks) do
+    if lh.old_count ~= lh.new_count then
+      local pairs_count = math.min(lh.old_count, lh.new_count)
+      for k = 0, pairs_count - 1 do
+        local oi = lh.old_start + k
+        local ni = lh.new_start + k
+        if group.del_lines[oi] and group.add_lines[ni] then
+          local ds, as = char_diff_pair(
+            group.del_lines[oi].text,
+            group.add_lines[ni].text,
+            group.del_lines[oi].idx,
+            group.add_lines[ni].idx,
+            diff_opts
+          )
+          vim.list_extend(all_del, ds)
+          vim.list_extend(all_add, as)
+        end
+      end
+    end
+  end
+
+  return all_del, all_add
+end
+
+---@param group diffs.ChangeGroup
+---@param handle table
+---@return diffs.CharSpan[], diffs.CharSpan[]
+local function diff_group_vscode(group, handle)
+  ---@type diffs.CharSpan[]
+  local all_del = {}
+  ---@type diffs.CharSpan[]
+  local all_add = {}
+
+  local ffi = require('ffi')
+
+  local old_texts = {}
+  for _, l in ipairs(group.del_lines) do
+    table.insert(old_texts, l.text)
+  end
+  local new_texts = {}
+  for _, l in ipairs(group.add_lines) do
+    table.insert(new_texts, l.text)
+  end
+
+  local orig_arr = ffi.new('const char*[?]', #old_texts)
+  for i, t in ipairs(old_texts) do
+    orig_arr[i - 1] = t
+  end
+
+  local mod_arr = ffi.new('const char*[?]', #new_texts)
+  for i, t in ipairs(new_texts) do
+    mod_arr[i - 1] = t
+  end
+
+  local opts = ffi.new('DiffsDiffOptions', {
+    ignore_trim_whitespace = false,
+    max_computation_time_ms = 1000,
+    compute_moves = false,
+    extend_to_subwords = false,
+  })
+
+  local result = handle.compute_diff(orig_arr, #old_texts, mod_arr, #new_texts, opts)
+  if result == nil then
+    return all_del, all_add
+  end
+
+  for ci = 0, result.changes.count - 1 do
+    local mapping = result.changes.mappings[ci]
+    for ii = 0, mapping.inner_change_count - 1 do
+      local inner = mapping.inner_changes[ii]
+
+      local orig_line = inner.original.start_line
+      if group.del_lines[orig_line] then
+        table.insert(all_del, {
+          line = group.del_lines[orig_line].idx,
+          col_start = inner.original.start_col,
+          col_end = inner.original.end_col,
+        })
+      end
+
+      local mod_line = inner.modified.start_line
+      if group.add_lines[mod_line] then
+        table.insert(all_add, {
+          line = group.add_lines[mod_line].idx,
+          col_start = inner.modified.start_col,
+          col_end = inner.modified.end_col,
+        })
+      end
+    end
+  end
+
+  handle.free_lines_diff(result)
+
+  return all_del, all_add
+end
+
+---@param hunk_lines string[]
+---@param algorithm? string
+---@return diffs.IntraChanges?
+function M.compute_intra_hunks(hunk_lines, algorithm)
+  local groups = M.extract_change_groups(hunk_lines)
+  if #groups == 0 then
+    return nil
+  end
+
+  algorithm = algorithm or 'default'
+
+  local vscode_handle = nil
+  if algorithm == 'vscode' then
+    vscode_handle = require('diffs.lib').load()
+    if not vscode_handle then
+      dbg('vscode algorithm requested but library not available, falling back to default')
+    end
+  end
+
+  ---@type diffs.DiffOpts?
+  local diff_opts = nil
+  if not vscode_handle then
+    diff_opts = parse_diffopt()
+    if diff_opts.algorithm then
+      dbg('diffopt algorithm: %s', diff_opts.algorithm)
+    end
+    if diff_opts.linematch then
+      dbg('diffopt linematch: %d', diff_opts.linematch)
+    end
+  end
+
+  ---@type diffs.CharSpan[]
+  local all_add = {}
+  ---@type diffs.CharSpan[]
+  local all_del = {}
+
+  dbg(
+    'intra: %d change groups, algorithm=%s, vscode=%s',
+    #groups,
+    algorithm,
+    vscode_handle and 'yes' or 'no'
+  )
+
+  for gi, group in ipairs(groups) do
+    dbg('group %d: %d del lines, %d add lines', gi, #group.del_lines, #group.add_lines)
+    local ds, as
+    if vscode_handle then
+      ds, as = diff_group_vscode(group, vscode_handle)
+    else
+      ds, as = diff_group_native(group, diff_opts)
+    end
+    dbg('group %d result: %d del spans, %d add spans', gi, #ds, #as)
+    for _, s in ipairs(ds) do
+      dbg('  del span: line=%d col=%d..%d', s.line, s.col_start, s.col_end)
+    end
+    for _, s in ipairs(as) do
+      dbg('  add span: line=%d col=%d..%d', s.line, s.col_start, s.col_end)
+    end
+    vim.list_extend(all_del, ds)
+    vim.list_extend(all_add, as)
+  end
+
+  if #all_add == 0 and #all_del == 0 then
+    return nil
+  end
+
+  return { add_spans = all_add, del_spans = all_del }
+end
+
+---@return boolean
+function M.has_vscode()
+  return require('diffs.lib').has_lib()
+end
+
+return M

lua/diffs/health.lua

@@ -15,6 +15,13 @@ function M.check()
   else
     vim.health.warn('vim-fugitive not detected (required for unified diff highlighting)')
   end
+
+  local lib = require('diffs.lib')
+  if lib.has_lib() then
+    vim.health.ok('libvscode_diff found at ' .. lib.lib_path())
+  else
+    vim.health.info('libvscode_diff not found (optional, using native vim.diff fallback)')
+  end
 end
 
 return M

lua/diffs/highlight.lua

@@ -1,6 +1,39 @@
 local M = {}
 
 local dbg = require('diffs.log').dbg
+local diff = require('diffs.diff')
+
+---@param filepath string
+---@param from_line integer
+---@param count integer
+---@return string[]
+local function read_line_range(filepath, from_line, count)
+  if count <= 0 then
+    return {}
+  end
+  local f = io.open(filepath, 'r')
+  if not f then
+    return {}
+  end
+  local result = {}
+  local line_num = 0
+  for line in f:lines() do
+    line_num = line_num + 1
+    if line_num >= from_line then
+      table.insert(result, line)
+      if #result >= count then
+        break
+      end
+    end
+  end
+  f:close()
+  return result
+end
+
+local PRIORITY_CLEAR = 198
+local PRIORITY_SYNTAX = 199
+local PRIORITY_LINE_BG = 200
+local PRIORITY_CHAR_BG = 201
 
 ---@param bufnr integer
 ---@param ns integer
@@ -8,9 +41,15 @@ local dbg = require('diffs.log').dbg
 ---@param col_offset integer
 ---@param text string
 ---@param lang string
+---@param context_lines? string[]
 ---@return integer
-local function highlight_text(bufnr, ns, hunk, col_offset, text, lang)
-  local ok, parser_obj = pcall(vim.treesitter.get_string_parser, text, lang)
+local function highlight_text(bufnr, ns, hunk, col_offset, text, lang, context_lines)
+  local parse_text = text
+  if context_lines and #context_lines > 0 then
+    parse_text = text .. '\n' .. table.concat(context_lines, '\n')
+  end
+
+  local ok, parser_obj = pcall(vim.treesitter.get_string_parser, parse_text, lang)
   if not ok or not parser_obj then
     return 0
   end
@@ -28,24 +67,26 @@ local function highlight_text(bufnr, ns, hunk, col_offset, text, lang)
   local extmark_count = 0
   local header_line = hunk.start_line - 1
 
-  for id, node, metadata in query:iter_captures(trees[1]:root(), text) do
-    local capture_name = '@' .. query.captures[id] .. '.' .. lang
-    local sr, sc, er, ec = node:range()
+  for id, node, metadata in query:iter_captures(trees[1]:root(), parse_text) do
+    local sr, sc, _, ec = node:range()
+    if sr == 0 then
+      local capture_name = '@' .. query.captures[id] .. '.' .. lang
 
-    local buf_sr = header_line + sr
-    local buf_er = header_line + er
-    local buf_sc = col_offset + sc
-    local buf_ec = col_offset + ec
+      local buf_sr = header_line
+      local buf_er = header_line
+      local buf_sc = col_offset + sc
+      local buf_ec = col_offset + ec
 
-    local priority = lang == 'diff' and (tonumber(metadata.priority) or 100) or 200
+      local priority = lang == 'diff' and (tonumber(metadata.priority) or 100) or PRIORITY_SYNTAX
 
-    pcall(vim.api.nvim_buf_set_extmark, bufnr, ns, buf_sr, buf_sc, {
-      end_row = buf_er,
-      end_col = buf_ec,
-      hl_group = capture_name,
-      priority = priority,
-    })
-    extmark_count = extmark_count + 1
+      pcall(vim.api.nvim_buf_set_extmark, bufnr, ns, buf_sr, buf_sc, {
+        end_row = buf_er,
+        end_col = buf_ec,
+        hl_group = capture_name,
+        priority = priority,
+      })
+      extmark_count = extmark_count + 1
+    end
   end
 
   return extmark_count
@@ -57,16 +98,21 @@ end
 
 ---@param bufnr integer
 ---@param ns integer
----@param hunk diffs.Hunk
 ---@param code_lines string[]
----@param col_offset integer?
+---@param lang string
+---@param line_map table<integer, integer>
+---@param col_offset integer
+---@param covered_lines? table<integer, true>
 ---@return integer
-local function highlight_treesitter(bufnr, ns, hunk, code_lines, col_offset)
-  local lang = hunk.lang
-  if not lang then
-    return 0
-  end
-
+local function highlight_treesitter(
+  bufnr,
+  ns,
+  code_lines,
+  lang,
+  line_map,
+  col_offset,
+  covered_lines
+)
   local code = table.concat(code_lines, '\n')
   if code == '' then
     return 0
@@ -78,54 +124,50 @@ local function highlight_treesitter(bufnr, ns, hunk, code_lines, col_offset)
     return 0
   end
 
-  local trees = parser_obj:parse()
+  local trees = parser_obj:parse(true)
   if not trees or #trees == 0 then
     dbg('parse returned no trees for lang: %s', lang)
     return 0
   end
 
-  local query = vim.treesitter.query.get(lang, 'highlights')
-  if not query then
-    dbg('no highlights query for lang: %s', lang)
-    return 0
-  end
-
-  if hunk.header_context and hunk.header_context_col then
-    local header_line = hunk.start_line - 1
-    pcall(vim.api.nvim_buf_set_extmark, bufnr, ns, header_line, hunk.header_context_col, {
-      end_col = hunk.header_context_col + #hunk.header_context,
-      hl_group = 'Normal',
-      priority = 199,
-    })
-    local header_extmarks =
-      highlight_text(bufnr, ns, hunk, hunk.header_context_col, hunk.header_context, lang)
-    if header_extmarks > 0 then
-      dbg('header %s:%d applied %d extmarks', hunk.filename, hunk.start_line, header_extmarks)
-    end
-  end
-
-  col_offset = col_offset or 1
-
   local extmark_count = 0
-  for id, node, metadata in query:iter_captures(trees[1]:root(), code) do
-    local capture_name = '@' .. query.captures[id] .. '.' .. lang
-    local sr, sc, er, ec = node:range()
+  parser_obj:for_each_tree(function(tree, ltree)
+    local tree_lang = ltree:lang()
+    local query = vim.treesitter.query.get(tree_lang, 'highlights')
+    if not query then
+      return
+    end
 
-    local buf_sr = hunk.start_line + sr
-    local buf_er = hunk.start_line + er
-    local buf_sc = sc + col_offset
-    local buf_ec = ec + col_offset
+    for id, node, metadata in query:iter_captures(tree:root(), code) do
+      local capture = query.captures[id]
+      if capture ~= 'spell' and capture ~= 'nospell' then
+        local capture_name = '@' .. capture .. '.' .. tree_lang
+        local sr, sc, er, ec = node:range()
 
-    local priority = lang == 'diff' and (tonumber(metadata.priority) or 100) or 200
+        local buf_sr = line_map[sr]
+        if buf_sr then
+          local buf_er = line_map[er] or buf_sr
 
-    pcall(vim.api.nvim_buf_set_extmark, bufnr, ns, buf_sr, buf_sc, {
-      end_row = buf_er,
-      end_col = buf_ec,
-      hl_group = capture_name,
-      priority = priority,
-    })
-    extmark_count = extmark_count + 1
-  end
+          local buf_sc = sc + col_offset
+          local buf_ec = ec + col_offset
+
+          local priority = tree_lang == 'diff' and (tonumber(metadata.priority) or 100)
+            or PRIORITY_SYNTAX
+
+          pcall(vim.api.nvim_buf_set_extmark, bufnr, ns, buf_sr, buf_sc, {
+            end_row = buf_er,
+            end_col = buf_ec,
+            hl_group = capture_name,
+            priority = priority,
+          })
+          extmark_count = extmark_count + 1
+          if covered_lines then
+            covered_lines[buf_sr] = true
+          end
+        end
+      end
+    end
+  end)
 
   return extmark_count
 end
@@ -175,8 +217,10 @@ end
 ---@param ns integer
 ---@param hunk diffs.Hunk
 ---@param code_lines string[]
+---@param covered_lines? table<integer, true>
+---@param leading_offset? integer
 ---@return integer
-local function highlight_vim_syntax(bufnr, ns, hunk, code_lines)
+local function highlight_vim_syntax(bufnr, ns, hunk, code_lines, covered_lines, leading_offset)
   local ft = hunk.ft
   if not ft then
     return 0
@@ -186,6 +230,8 @@ local function highlight_vim_syntax(bufnr, ns, hunk, code_lines)
     return 0
   end
 
+  leading_offset = leading_offset or 0
+
   local scratch = vim.api.nvim_create_buf(false, true)
   vim.api.nvim_buf_set_lines(scratch, 0, -1, false, code_lines)
   vim.api.nvim_set_option_value('bufhidden', 'wipe', { buf = scratch })
@@ -212,15 +258,22 @@ local function highlight_vim_syntax(bufnr, ns, hunk, code_lines)
 
   vim.api.nvim_buf_delete(scratch, { force = true })
 
+  local hunk_line_count = #hunk.lines
   local extmark_count = 0
   for _, span in ipairs(spans) do
-    local buf_line = hunk.start_line + span.line - 1
-    pcall(vim.api.nvim_buf_set_extmark, bufnr, ns, buf_line, span.col_start, {
-      end_col = span.col_end,
-      hl_group = span.hl_name,
-      priority = 200,
-    })
-    extmark_count = extmark_count + 1
+    local adj = span.line - leading_offset
+    if adj >= 1 and adj <= hunk_line_count then
+      local buf_line = hunk.start_line + adj - 1
+      pcall(vim.api.nvim_buf_set_extmark, bufnr, ns, buf_line, span.col_start, {
+        end_col = span.col_end,
+        hl_group = span.hl_name,
+        priority = PRIORITY_SYNTAX,
+      })
+      extmark_count = extmark_count + 1
+      if covered_lines then
+        covered_lines[buf_line] = true
+      end
+    end
   end
 
   return extmark_count
@@ -247,21 +300,101 @@ function M.highlight_hunk(bufnr, ns, hunk, opts)
     use_vim = false
   end
 
-  local apply_syntax = use_ts or use_vim
+  ---@type table<integer, true>
+  local covered_lines = {}
 
-  ---@type string[]
-  local code_lines = {}
-  if apply_syntax then
-    for _, line in ipairs(hunk.lines) do
-      table.insert(code_lines, line:sub(2))
+  local ctx_cfg = opts.highlights.context
+  local context = (ctx_cfg and ctx_cfg.enabled) and ctx_cfg.lines or 0
+  local leading = {}
+  local trailing = {}
+  if (use_ts or use_vim) and context > 0 and hunk.file_new_start and hunk.repo_root then
+    local filepath = vim.fs.joinpath(hunk.repo_root, hunk.filename)
+    local lead_from = math.max(1, hunk.file_new_start - context)
+    local lead_count = hunk.file_new_start - lead_from
+    if lead_count > 0 then
+      leading = read_line_range(filepath, lead_from, lead_count)
     end
+    local trail_from = hunk.file_new_start + (hunk.file_new_count or 0)
+    trailing = read_line_range(filepath, trail_from, context)
   end
 
   local extmark_count = 0
   if use_ts then
-    extmark_count = highlight_treesitter(bufnr, ns, hunk, code_lines)
+    ---@type string[]
+    local new_code = {}
+    ---@type table<integer, integer>
+    local new_map = {}
+    ---@type string[]
+    local old_code = {}
+    ---@type table<integer, integer>
+    local old_map = {}
+
+    for _, pad_line in ipairs(leading) do
+      table.insert(new_code, pad_line)
+      table.insert(old_code, pad_line)
+    end
+
+    for i, line in ipairs(hunk.lines) do
+      local prefix = line:sub(1, 1)
+      local stripped = line:sub(2)
+      local buf_line = hunk.start_line + i - 1
+
+      if prefix == '+' then
+        new_map[#new_code] = buf_line
+        table.insert(new_code, stripped)
+      elseif prefix == '-' then
+        old_map[#old_code] = buf_line
+        table.insert(old_code, stripped)
+      else
+        new_map[#new_code] = buf_line
+        table.insert(new_code, stripped)
+        table.insert(old_code, stripped)
+      end
+    end
+
+    for _, pad_line in ipairs(trailing) do
+      table.insert(new_code, pad_line)
+      table.insert(old_code, pad_line)
+    end
+
+    extmark_count = highlight_treesitter(bufnr, ns, new_code, hunk.lang, new_map, 1, covered_lines)
+    extmark_count = extmark_count
+      + highlight_treesitter(bufnr, ns, old_code, hunk.lang, old_map, 1, covered_lines)
+
+    if hunk.header_context and hunk.header_context_col then
+      local header_line = hunk.start_line - 1
+      pcall(vim.api.nvim_buf_set_extmark, bufnr, ns, header_line, hunk.header_context_col, {
+        end_col = hunk.header_context_col + #hunk.header_context,
+        hl_group = 'DiffsClear',
+        priority = PRIORITY_CLEAR,
+      })
+      local header_extmarks = highlight_text(
+        bufnr,
+        ns,
+        hunk,
+        hunk.header_context_col,
+        hunk.header_context,
+        hunk.lang,
+        new_code
+      )
+      if header_extmarks > 0 then
+        dbg('header %s:%d applied %d extmarks', hunk.filename, hunk.start_line, header_extmarks)
+      end
+      extmark_count = extmark_count + header_extmarks
+    end
   elseif use_vim then
-    extmark_count = highlight_vim_syntax(bufnr, ns, hunk, code_lines)
+    ---@type string[]
+    local code_lines = {}
+    for _, pad_line in ipairs(leading) do
+      table.insert(code_lines, pad_line)
+    end
+    for _, line in ipairs(hunk.lines) do
+      table.insert(code_lines, line:sub(2))
+    end
+    for _, pad_line in ipairs(trailing) do
+      table.insert(code_lines, pad_line)
+    end
+    extmark_count = highlight_vim_syntax(bufnr, ns, hunk, code_lines, covered_lines, #leading)
   end
 
   if
@@ -270,17 +403,48 @@ function M.highlight_hunk(bufnr, ns, hunk, opts)
     and #hunk.header_lines > 0
     and opts.highlights.treesitter.enabled
   then
+    ---@type table<integer, integer>
+    local header_map = {}
+    for i = 0, #hunk.header_lines - 1 do
+      header_map[i] = hunk.header_start_line - 1 + i
+    end
     extmark_count = extmark_count
-      + highlight_treesitter(bufnr, ns, {
-        filename = hunk.filename,
-        start_line = hunk.header_start_line - 1,
-        lang = 'diff',
-        lines = hunk.header_lines,
-        header_lines = {},
-      }, hunk.header_lines, 0)
+      + highlight_treesitter(bufnr, ns, hunk.header_lines, 'diff', header_map, 0)
   end
 
-  local syntax_applied = extmark_count > 0
+  ---@type diffs.IntraChanges?
+  local intra = nil
+  local intra_cfg = opts.highlights.intra
+  if intra_cfg and intra_cfg.enabled and #hunk.lines <= intra_cfg.max_lines then
+    dbg('computing intra for hunk %s:%d (%d lines)', hunk.filename, hunk.start_line, #hunk.lines)
+    intra = diff.compute_intra_hunks(hunk.lines, intra_cfg.algorithm)
+    if intra then
+      dbg('intra result: %d add spans, %d del spans', #intra.add_spans, #intra.del_spans)
+    else
+      dbg('intra result: nil (no change groups)')
+    end
+  elseif intra_cfg and not intra_cfg.enabled then
+    dbg('intra disabled by config')
+  elseif intra_cfg and #hunk.lines > intra_cfg.max_lines then
+    dbg('intra skipped: %d lines > %d max', #hunk.lines, intra_cfg.max_lines)
+  end
+
+  ---@type table<integer, diffs.CharSpan[]>
+  local char_spans_by_line = {}
+  if intra then
+    for _, span in ipairs(intra.add_spans) do
+      if not char_spans_by_line[span.line] then
+        char_spans_by_line[span.line] = {}
+      end
+      table.insert(char_spans_by_line[span.line], span)
+    end
+    for _, span in ipairs(intra.del_spans) do
+      if not char_spans_by_line[span.line] then
+        char_spans_by_line[span.line] = {}
+      end
+      table.insert(char_spans_by_line[span.line], span)
+    end
+  end
 
   for i, line in ipairs(hunk.lines) do
     local buf_line = hunk.start_line + i - 1
@@ -299,24 +463,52 @@ function M.highlight_hunk(bufnr, ns, hunk, opts)
       })
     end
 
-    if opts.highlights.background and is_diff_line then
-      local extmark_opts = {
-        line_hl_group = line_hl,
-        priority = 198,
-      }
-      if opts.highlights.gutter then
-        extmark_opts.number_hl_group = number_hl
-      end
-      pcall(vim.api.nvim_buf_set_extmark, bufnr, ns, buf_line, 0, extmark_opts)
-    end
-
-    if line_len > 1 and syntax_applied then
+    if line_len > 1 and covered_lines[buf_line] then
       pcall(vim.api.nvim_buf_set_extmark, bufnr, ns, buf_line, 1, {
         end_col = line_len,
-        hl_group = 'Normal',
-        priority = 199,
+        hl_group = 'DiffsClear',
+        priority = PRIORITY_CLEAR,
       })
     end
+
+    if opts.highlights.background and is_diff_line then
+      pcall(vim.api.nvim_buf_set_extmark, bufnr, ns, buf_line, 0, {
+        end_row = buf_line + 1,
+        hl_group = line_hl,
+        hl_eol = true,
+        priority = PRIORITY_LINE_BG,
+      })
+      if opts.highlights.gutter then
+        pcall(vim.api.nvim_buf_set_extmark, bufnr, ns, buf_line, 0, {
+          number_hl_group = number_hl,
+          priority = PRIORITY_LINE_BG,
+        })
+      end
+    end
+
+    if char_spans_by_line[i] then
+      local char_hl = prefix == '+' and 'DiffsAddText' or 'DiffsDeleteText'
+      for _, span in ipairs(char_spans_by_line[i]) do
+        dbg(
+          'char extmark: line=%d buf_line=%d col=%d..%d hl=%s text="%s"',
+          i,
+          buf_line,
+          span.col_start,
+          span.col_end,
+          char_hl,
+          line:sub(span.col_start + 1, span.col_end)
+        )
+        local ok, err = pcall(vim.api.nvim_buf_set_extmark, bufnr, ns, buf_line, span.col_start, {
+          end_col = span.col_end,
+          hl_group = char_hl,
+          priority = PRIORITY_CHAR_BG,
+        })
+        if not ok then
+          dbg('char extmark FAILED: %s', err)
+        end
+        extmark_count = extmark_count + 1
+      end
+    end
   end
 
   dbg('hunk %s:%d applied %d extmarks', hunk.filename, hunk.start_line, extmark_count)

lua/diffs/init.lua

@@ -6,22 +6,50 @@
 ---@field enabled boolean
 ---@field max_lines integer
 
+---@class diffs.IntraConfig
+---@field enabled boolean
+---@field algorithm string
+---@field max_lines integer
+
+---@class diffs.ContextConfig
+---@field enabled boolean
+---@field lines integer
+
 ---@class diffs.Highlights
 ---@field background boolean
 ---@field gutter boolean
+---@field blend_alpha? number
+---@field overrides? table<string, table>
+---@field context diffs.ContextConfig
 ---@field treesitter diffs.TreesitterConfig
 ---@field vim diffs.VimConfig
+---@field intra diffs.IntraConfig
 
 ---@class diffs.FugitiveConfig
 ---@field horizontal string|false
 ---@field vertical string|false
 
+---@class diffs.ConflictKeymaps
+---@field ours string|false
+---@field theirs string|false
+---@field both string|false
+---@field none string|false
+---@field next string|false
+---@field prev string|false
+
+---@class diffs.ConflictConfig
+---@field enabled boolean
+---@field disable_diagnostics boolean
+---@field show_virtual_text boolean
+---@field keymaps diffs.ConflictKeymaps
+
 ---@class diffs.Config
 ---@field debug boolean
 ---@field debounce_ms integer
 ---@field hide_prefix boolean
 ---@field highlights diffs.Highlights
 ---@field fugitive diffs.FugitiveConfig
+---@field conflict diffs.ConflictConfig
 
 ---@class diffs
 ---@field attach fun(bufnr?: integer)
@@ -74,6 +102,10 @@ local default_config = {
   highlights = {
     background = true,
     gutter = true,
+    context = {
+      enabled = true,
+      lines = 25,
+    },
     treesitter = {
       enabled = true,
       max_lines = 500,
@@ -82,11 +114,29 @@ local default_config = {
       enabled = false,
       max_lines = 200,
     },
+    intra = {
+      enabled = true,
+      algorithm = 'default',
+      max_lines = 500,
+    },
   },
   fugitive = {
     horizontal = 'du',
     vertical = 'dU',
   },
+  conflict = {
+    enabled = true,
+    disable_diagnostics = true,
+    show_virtual_text = true,
+    keymaps = {
+      ours = 'doo',
+      theirs = 'dot',
+      both = 'dob',
+      none = 'don',
+      next = ']x',
+      prev = '[x',
+    },
+  },
 }
 
 ---@type diffs.Config
@@ -172,18 +222,79 @@ local function compute_highlight_groups()
   local blended_add = blend_color(add_bg, bg, 0.4)
   local blended_del = blend_color(del_bg, bg, 0.4)
 
+  local alpha = config.highlights.blend_alpha or 0.6
+  local blended_add_text = blend_color(add_fg, bg, alpha)
+  local blended_del_text = blend_color(del_fg, bg, alpha)
+
+  vim.api.nvim_set_hl(0, 'DiffsClear', { default = true, fg = normal.fg or 0xc0c0c0 })
   vim.api.nvim_set_hl(0, 'DiffsAdd', { default = true, bg = blended_add })
   vim.api.nvim_set_hl(0, 'DiffsDelete', { default = true, bg = blended_del })
-  vim.api.nvim_set_hl(0, 'DiffsAddNr', { default = true, fg = add_fg, bg = blended_add })
-  vim.api.nvim_set_hl(0, 'DiffsDeleteNr', { default = true, fg = del_fg, bg = blended_del })
+  vim.api.nvim_set_hl(0, 'DiffsAddNr', { default = true, fg = blended_add_text, bg = blended_add })
+  vim.api.nvim_set_hl(
+    0,
+    'DiffsDeleteNr',
+    { default = true, fg = blended_del_text, bg = blended_del }
+  )
+  vim.api.nvim_set_hl(0, 'DiffsAddText', { default = true, bg = blended_add_text })
+  vim.api.nvim_set_hl(0, 'DiffsDeleteText', { default = true, bg = blended_del_text })
+
+  dbg('highlight groups: Normal.bg=#%06x DiffAdd.bg=#%06x diffAdded.fg=#%06x', bg, add_bg, add_fg)
+  dbg(
+    'DiffsAdd.bg=#%06x DiffsAddText.bg=#%06x DiffsAddNr.fg=#%06x',
+    blended_add,
+    blended_add_text,
+    add_fg
+  )
+  dbg('DiffsDelete.bg=#%06x DiffsDeleteText.bg=#%06x', blended_del, blended_del_text)
 
   local diff_change = resolve_hl('DiffChange')
   local diff_text = resolve_hl('DiffText')
 
-  vim.api.nvim_set_hl(0, 'DiffsDiffAdd', { bg = diff_add.bg })
-  vim.api.nvim_set_hl(0, 'DiffsDiffDelete', { fg = diff_delete.fg, bg = diff_delete.bg })
-  vim.api.nvim_set_hl(0, 'DiffsDiffChange', { bg = diff_change.bg })
-  vim.api.nvim_set_hl(0, 'DiffsDiffText', { bg = diff_text.bg })
+  vim.api.nvim_set_hl(0, 'DiffsDiffAdd', { default = true, bg = diff_add.bg })
+  vim.api.nvim_set_hl(
+    0,
+    'DiffsDiffDelete',
+    { default = true, fg = diff_delete.fg, bg = diff_delete.bg }
+  )
+  vim.api.nvim_set_hl(0, 'DiffsDiffChange', { default = true, bg = diff_change.bg })
+  vim.api.nvim_set_hl(0, 'DiffsDiffText', { default = true, bg = diff_text.bg })
+
+  local change_bg = diff_change.bg or 0x3a3a4a
+  local text_bg = diff_text.bg or 0x4a4a5a
+  local change_fg = diff_change.fg or diff_text.fg or 0x80a0c0
+
+  local blended_ours = blend_color(add_bg, bg, 0.4)
+  local blended_theirs = blend_color(change_bg, bg, 0.4)
+  local blended_base = blend_color(text_bg, bg, 0.3)
+  local blended_ours_nr = blend_color(add_fg, bg, alpha)
+  local blended_theirs_nr = blend_color(change_fg, bg, alpha)
+  local blended_base_nr = blend_color(change_fg, bg, 0.4)
+
+  vim.api.nvim_set_hl(0, 'DiffsConflictOurs', { default = true, bg = blended_ours })
+  vim.api.nvim_set_hl(0, 'DiffsConflictTheirs', { default = true, bg = blended_theirs })
+  vim.api.nvim_set_hl(0, 'DiffsConflictBase', { default = true, bg = blended_base })
+  vim.api.nvim_set_hl(0, 'DiffsConflictMarker', { default = true, fg = 0x808080, bold = true })
+  vim.api.nvim_set_hl(
+    0,
+    'DiffsConflictOursNr',
+    { default = true, fg = blended_ours_nr, bg = blended_ours }
+  )
+  vim.api.nvim_set_hl(
+    0,
+    'DiffsConflictTheirsNr',
+    { default = true, fg = blended_theirs_nr, bg = blended_theirs }
+  )
+  vim.api.nvim_set_hl(
+    0,
+    'DiffsConflictBaseNr',
+    { default = true, fg = blended_base_nr, bg = blended_base }
+  )
+
+  if config.highlights.overrides then
+    for group, hl in pairs(config.highlights.overrides) do
+      vim.api.nvim_set_hl(0, group, hl)
+    end
+  end
 end
 
 local function init()
@@ -205,10 +316,21 @@ local function init()
     vim.validate({
       ['highlights.background'] = { opts.highlights.background, 'boolean', true },
       ['highlights.gutter'] = { opts.highlights.gutter, 'boolean', true },
+      ['highlights.blend_alpha'] = { opts.highlights.blend_alpha, 'number', true },
+      ['highlights.overrides'] = { opts.highlights.overrides, 'table', true },
+      ['highlights.context'] = { opts.highlights.context, 'table', true },
       ['highlights.treesitter'] = { opts.highlights.treesitter, 'table', true },
       ['highlights.vim'] = { opts.highlights.vim, 'table', true },
+      ['highlights.intra'] = { opts.highlights.intra, 'table', true },
     })
 
+    if opts.highlights.context then
+      vim.validate({
+        ['highlights.context.enabled'] = { opts.highlights.context.enabled, 'boolean', true },
+        ['highlights.context.lines'] = { opts.highlights.context.lines, 'number', true },
+      })
+    end
+
     if opts.highlights.treesitter then
       vim.validate({
         ['highlights.treesitter.enabled'] = { opts.highlights.treesitter.enabled, 'boolean', true },
@@ -226,6 +348,20 @@ local function init()
         ['highlights.vim.max_lines'] = { opts.highlights.vim.max_lines, 'number', true },
       })
     end
+
+    if opts.highlights.intra then
+      vim.validate({
+        ['highlights.intra.enabled'] = { opts.highlights.intra.enabled, 'boolean', true },
+        ['highlights.intra.algorithm'] = {
+          opts.highlights.intra.algorithm,
+          function(v)
+            return v == nil or v == 'default' or v == 'vscode'
+          end,
+          "'default' or 'vscode'",
+        },
+        ['highlights.intra.max_lines'] = { opts.highlights.intra.max_lines, 'number', true },
+      })
+    end
   end
 
   if opts.fugitive then
@@ -247,9 +383,41 @@ local function init()
     })
   end
 
+  if opts.conflict then
+    vim.validate({
+      ['conflict.enabled'] = { opts.conflict.enabled, 'boolean', true },
+      ['conflict.disable_diagnostics'] = { opts.conflict.disable_diagnostics, 'boolean', true },
+      ['conflict.show_virtual_text'] = { opts.conflict.show_virtual_text, 'boolean', true },
+      ['conflict.keymaps'] = { opts.conflict.keymaps, 'table', true },
+    })
+
+    if opts.conflict.keymaps then
+      local keymap_validator = function(v)
+        return v == false or type(v) == 'string'
+      end
+      for _, key in ipairs({ 'ours', 'theirs', 'both', 'none', 'next', 'prev' }) do
+        vim.validate({
+          ['conflict.keymaps.' .. key] = {
+            opts.conflict.keymaps[key],
+            keymap_validator,
+            'string or false',
+          },
+        })
+      end
+    end
+  end
+
   if opts.debounce_ms and opts.debounce_ms < 0 then
     error('diffs: debounce_ms must be >= 0')
   end
+  if
+    opts.highlights
+    and opts.highlights.context
+    and opts.highlights.context.lines
+    and opts.highlights.context.lines < 0
+  then
+    error('diffs: highlights.context.lines must be >= 0')
+  end
   if
     opts.highlights
     and opts.highlights.treesitter
@@ -266,6 +434,21 @@ local function init()
   then
     error('diffs: highlights.vim.max_lines must be >= 1')
   end
+  if
+    opts.highlights
+    and opts.highlights.intra
+    and opts.highlights.intra.max_lines
+    and opts.highlights.intra.max_lines < 1
+  then
+    error('diffs: highlights.intra.max_lines must be >= 1')
+  end
+  if
+    opts.highlights
+    and opts.highlights.blend_alpha
+    and (opts.highlights.blend_alpha < 0 or opts.highlights.blend_alpha > 1)
+  then
+    error('diffs: highlights.blend_alpha must be >= 0 and <= 1')
+  end
 
   config = vim.tbl_deep_extend('force', default_config, opts)
   log.set_enabled(config.debug)
@@ -388,4 +571,10 @@ function M.get_fugitive_config()
   return config.fugitive
 end
 
+---@return diffs.ConflictConfig
+function M.get_conflict_config()
+  init()
+  return config.conflict
+end
+
 return M

lua/diffs/lib.lua

@@ -0,0 +1,214 @@
+local M = {}
+
+local dbg = require('diffs.log').dbg
+
+---@type table?
+local cached_handle = nil
+
+---@type boolean
+local download_in_progress = false
+
+---@return string
+local function get_os()
+  local os_name = jit.os:lower()
+  if os_name == 'osx' then
+    return 'macos'
+  end
+  return os_name
+end
+
+---@return string
+local function get_arch()
+  return jit.arch:lower()
+end
+
+---@return string
+local function get_ext()
+  local os_name = jit.os:lower()
+  if os_name == 'windows' then
+    return 'dll'
+  elseif os_name == 'osx' then
+    return 'dylib'
+  end
+  return 'so'
+end
+
+---@return string
+local function lib_dir()
+  return vim.fn.stdpath('data') .. '/diffs/lib'
+end
+
+---@return string
+local function lib_path()
+  return lib_dir() .. '/libvscode_diff.' .. get_ext()
+end
+
+---@return string
+local function version_path()
+  return lib_dir() .. '/version'
+end
+
+local EXPECTED_VERSION = '2.18.0'
+
+---@return boolean
+function M.has_lib()
+  if cached_handle then
+    return true
+  end
+  return vim.fn.filereadable(lib_path()) == 1
+end
+
+---@return string
+function M.lib_path()
+  return lib_path()
+end
+
+---@return table?
+function M.load()
+  if cached_handle then
+    return cached_handle
+  end
+
+  local path = lib_path()
+  if vim.fn.filereadable(path) ~= 1 then
+    return nil
+  end
+
+  local ffi = require('ffi')
+
+  ffi.cdef([[
+    typedef struct {
+      int start_line;
+      int end_line;
+    } DiffsLineRange;
+
+    typedef struct {
+      int start_line;
+      int start_col;
+      int end_line;
+      int end_col;
+    } DiffsCharRange;
+
+    typedef struct {
+      DiffsCharRange original;
+      DiffsCharRange modified;
+    } DiffsRangeMapping;
+
+    typedef struct {
+      DiffsLineRange original;
+      DiffsLineRange modified;
+      DiffsRangeMapping* inner_changes;
+      int inner_change_count;
+    } DiffsDetailedMapping;
+
+    typedef struct {
+      DiffsDetailedMapping* mappings;
+      int count;
+      int capacity;
+    } DiffsDetailedMappingArray;
+
+    typedef struct {
+      DiffsLineRange original;
+      DiffsLineRange modified;
+    } DiffsMovedText;
+
+    typedef struct {
+      DiffsMovedText* moves;
+      int count;
+      int capacity;
+    } DiffsMovedTextArray;
+
+    typedef struct {
+      DiffsDetailedMappingArray changes;
+      DiffsMovedTextArray moves;
+      bool hit_timeout;
+    } DiffsLinesDiff;
+
+    typedef struct {
+      bool ignore_trim_whitespace;
+      int max_computation_time_ms;
+      bool compute_moves;
+      bool extend_to_subwords;
+    } DiffsDiffOptions;
+
+    DiffsLinesDiff* compute_diff(
+      const char** original_lines,
+      int original_count,
+      const char** modified_lines,
+      int modified_count,
+      const DiffsDiffOptions* options
+    );
+
+    void free_lines_diff(DiffsLinesDiff* diff);
+  ]])
+
+  local ok, handle = pcall(ffi.load, path)
+  if not ok then
+    dbg('failed to load libvscode_diff: %s', handle)
+    return nil
+  end
+
+  cached_handle = handle
+  return handle
+end
+
+---@param callback fun(handle: table?)
+function M.ensure(callback)
+  if cached_handle then
+    callback(cached_handle)
+    return
+  end
+
+  if M.has_lib() then
+    callback(M.load())
+    return
+  end
+
+  if download_in_progress then
+    dbg('download already in progress')
+    callback(nil)
+    return
+  end
+
+  download_in_progress = true
+
+  local dir = lib_dir()
+  vim.fn.mkdir(dir, 'p')
+
+  local os_name = get_os()
+  local arch = get_arch()
+  local ext = get_ext()
+  local filename = ('libvscode_diff_%s_%s_%s.%s'):format(os_name, arch, EXPECTED_VERSION, ext)
+  local url = ('https://github.com/esmuellert/vscode-diff.nvim/releases/download/v%s/%s'):format(
+    EXPECTED_VERSION,
+    filename
+  )
+
+  local dest = lib_path()
+  vim.notify('[diffs] downloading libvscode_diff...', vim.log.levels.INFO)
+
+  local cmd = { 'curl', '-fSL', '-o', dest, url }
+
+  vim.system(cmd, {}, function(result)
+    download_in_progress = false
+    vim.schedule(function()
+      if result.code ~= 0 then
+        vim.notify('[diffs] failed to download libvscode_diff', vim.log.levels.WARN)
+        dbg('curl failed: %s', result.stderr or '')
+        callback(nil)
+        return
+      end
+
+      local f = io.open(version_path(), 'w')
+      if f then
+        f:write(EXPECTED_VERSION)
+        f:close()
+      end
+
+      vim.notify('[diffs] libvscode_diff downloaded', vim.log.levels.INFO)
+      callback(M.load())
+    end)
+  end)
+end
+
+return M

lua/diffs/parser.lua

@@ -8,17 +8,43 @@
 ---@field lines string[]
 ---@field header_start_line integer?
 ---@field header_lines string[]?
+---@field file_old_start integer?
+---@field file_old_count integer?
+---@field file_new_start integer?
+---@field file_new_count integer?
+---@field repo_root string?
 
 local M = {}
 
 local dbg = require('diffs.log').dbg
 
+---@param filepath string
+---@param n integer
+---@return string[]?
+local function read_first_lines(filepath, n)
+  local f = io.open(filepath, 'r')
+  if not f then
+    return nil
+  end
+  local lines = {}
+  for _ = 1, n do
+    local line = f:read('*l')
+    if not line then
+      break
+    end
+    table.insert(lines, line)
+  end
+  f:close()
+  return #lines > 0 and lines or nil
+end
+
 ---@param filename string
 ---@param repo_root string?
 ---@return string?
 local function get_ft_from_filename(filename, repo_root)
   if repo_root then
     local full_path = vim.fs.joinpath(repo_root, filename)
+
     local buf = vim.fn.bufnr(full_path)
     if buf ~= -1 then
       local ft = vim.api.nvim_get_option_value('filetype', { buf = buf })
@@ -30,10 +56,25 @@ local function get_ft_from_filename(filename, repo_root)
   end
 
   local ft = vim.filetype.match({ filename = filename })
-  if not ft then
-    dbg('no filetype for: %s', filename)
+  if ft then
+    dbg('filetype from filename: %s', ft)
+    return ft
   end
-  return ft
+
+  if repo_root then
+    local full_path = vim.fs.joinpath(repo_root, filename)
+    local contents = read_first_lines(full_path, 10)
+    if contents then
+      ft = vim.filetype.match({ filename = filename, contents = contents })
+      if ft then
+        dbg('filetype from file content: %s', ft)
+        return ft
+      end
+    end
+  end
+
+  dbg('no filetype for: %s', filename)
+  return nil
 end
 
 ---@param ft string
@@ -96,6 +137,14 @@ function M.parse_buffer(bufnr)
   local header_start = nil
   ---@type string[]
   local header_lines = {}
+  ---@type integer?
+  local file_old_start = nil
+  ---@type integer?
+  local file_old_count = nil
+  ---@type integer?
+  local file_new_start = nil
+  ---@type integer?
+  local file_new_count = nil
 
   local function flush_hunk()
     if hunk_start and #hunk_lines > 0 then
@@ -107,6 +156,11 @@ function M.parse_buffer(bufnr)
         header_context = hunk_header_context,
         header_context_col = hunk_header_context_col,
         lines = hunk_lines,
+        file_old_start = file_old_start,
+        file_old_count = file_old_count,
+        file_new_start = file_new_start,
+        file_new_count = file_new_count,
+        repo_root = repo_root,
       }
       if hunk_count == 1 and header_start and #header_lines > 0 then
         hunk.header_start_line = header_start
@@ -118,6 +172,10 @@ function M.parse_buffer(bufnr)
     hunk_header_context = nil
     hunk_header_context_col = nil
     hunk_lines = {}
+    file_old_start = nil
+    file_old_count = nil
+    file_new_start = nil
+    file_new_count = nil
   end
 
   for i, line in ipairs(lines) do
@@ -138,6 +196,13 @@ function M.parse_buffer(bufnr)
     elseif line:match('^@@.-@@') then
       flush_hunk()
       hunk_start = i
+      local hs, hc, hs2, hc2 = line:match('^@@ %-(%d+),?(%d*) %+(%d+),?(%d*) @@')
+      if hs then
+        file_old_start = tonumber(hs)
+        file_old_count = tonumber(hc) or 1
+        file_new_start = tonumber(hs2)
+        file_new_count = tonumber(hc2) or 1
+      end
       local prefix, context = line:match('^(@@.-@@%s*)(.*)')
       if context and context ~= '' then
         hunk_header_context = context

plugin/diffs.lua

@@ -23,6 +23,22 @@ vim.api.nvim_create_autocmd('FileType', {
   end,
 })
 
+vim.api.nvim_create_autocmd('BufReadCmd', {
+  pattern = 'diffs://*',
+  callback = function(args)
+    require('diffs.commands').read_buffer(args.buf)
+  end,
+})
+
+vim.api.nvim_create_autocmd('BufReadPost', {
+  callback = function(args)
+    local conflict_config = require('diffs').get_conflict_config()
+    if conflict_config.enabled then
+      require('diffs.conflict').attach(args.buf, conflict_config)
+    end
+  end,
+})
+
 vim.api.nvim_create_autocmd('OptionSet', {
   pattern = 'diff',
   callback = function()
@@ -33,3 +49,36 @@ vim.api.nvim_create_autocmd('OptionSet', {
     end
   end,
 })
+
+local cmds = require('diffs.commands')
+vim.keymap.set('n', '<Plug>(diffs-gdiff)', function()
+  cmds.gdiff(nil, false)
+end, { desc = 'Unified diff (horizontal)' })
+vim.keymap.set('n', '<Plug>(diffs-gvdiff)', function()
+  cmds.gdiff(nil, true)
+end, { desc = 'Unified diff (vertical)' })
+
+local function conflict_action(fn)
+  local bufnr = vim.api.nvim_get_current_buf()
+  local config = require('diffs').get_conflict_config()
+  fn(bufnr, config)
+end
+
+vim.keymap.set('n', '<Plug>(diffs-conflict-ours)', function()
+  conflict_action(require('diffs.conflict').resolve_ours)
+end, { desc = 'Accept current (ours) change' })
+vim.keymap.set('n', '<Plug>(diffs-conflict-theirs)', function()
+  conflict_action(require('diffs.conflict').resolve_theirs)
+end, { desc = 'Accept incoming (theirs) change' })
+vim.keymap.set('n', '<Plug>(diffs-conflict-both)', function()
+  conflict_action(require('diffs.conflict').resolve_both)
+end, { desc = 'Accept both changes' })
+vim.keymap.set('n', '<Plug>(diffs-conflict-none)', function()
+  conflict_action(require('diffs.conflict').resolve_none)
+end, { desc = 'Reject both changes' })
+vim.keymap.set('n', '<Plug>(diffs-conflict-next)', function()
+  require('diffs.conflict').goto_next(vim.api.nvim_get_current_buf())
+end, { desc = 'Jump to next conflict' })
+vim.keymap.set('n', '<Plug>(diffs-conflict-prev)', function()
+  require('diffs.conflict').goto_prev(vim.api.nvim_get_current_buf())
+end, { desc = 'Jump to previous conflict' })

spec/conflict_spec.lua

@@ -0,0 +1,688 @@
+local conflict = require('diffs.conflict')
+local helpers = require('spec.helpers')
+
+local function default_config(overrides)
+  local cfg = {
+    enabled = true,
+    disable_diagnostics = false,
+    show_virtual_text = true,
+    keymaps = {
+      ours = 'doo',
+      theirs = 'dot',
+      both = 'dob',
+      none = 'don',
+      next = ']x',
+      prev = '[x',
+    },
+  }
+  if overrides then
+    cfg = vim.tbl_deep_extend('force', cfg, overrides)
+  end
+  return cfg
+end
+
+local function create_file_buffer(lines)
+  local bufnr = vim.api.nvim_create_buf(false, false)
+  vim.api.nvim_buf_set_lines(bufnr, 0, -1, false, lines or {})
+  return bufnr
+end
+
+local function get_extmarks(bufnr)
+  return vim.api.nvim_buf_get_extmarks(bufnr, conflict.get_namespace(), 0, -1, { details = true })
+end
+
+describe('conflict', function()
+  describe('parse', function()
+    it('parses a single conflict', function()
+      local lines = {
+        '<<<<<<< HEAD',
+        'local x = 1',
+        '=======',
+        'local x = 2',
+        '>>>>>>> feature',
+      }
+      local regions = conflict.parse(lines)
+      assert.are.equal(1, #regions)
+      assert.are.equal(0, regions[1].marker_ours)
+      assert.are.equal(1, regions[1].ours_start)
+      assert.are.equal(2, regions[1].ours_end)
+      assert.are.equal(2, regions[1].marker_sep)
+      assert.are.equal(3, regions[1].theirs_start)
+      assert.are.equal(4, regions[1].theirs_end)
+      assert.are.equal(4, regions[1].marker_theirs)
+    end)
+
+    it('parses multiple conflicts', function()
+      local lines = {
+        '<<<<<<< HEAD',
+        'a',
+        '=======',
+        'b',
+        '>>>>>>> feat',
+        'normal line',
+        '<<<<<<< HEAD',
+        'c',
+        '=======',
+        'd',
+        '>>>>>>> feat',
+      }
+      local regions = conflict.parse(lines)
+      assert.are.equal(2, #regions)
+      assert.are.equal(0, regions[1].marker_ours)
+      assert.are.equal(6, regions[2].marker_ours)
+    end)
+
+    it('parses diff3 format', function()
+      local lines = {
+        '<<<<<<< HEAD',
+        'local x = 1',
+        '||||||| base',
+        'local x = 0',
+        '=======',
+        'local x = 2',
+        '>>>>>>> feature',
+      }
+      local regions = conflict.parse(lines)
+      assert.are.equal(1, #regions)
+      assert.are.equal(2, regions[1].marker_base)
+      assert.are.equal(3, regions[1].base_start)
+      assert.are.equal(4, regions[1].base_end)
+    end)
+
+    it('handles empty ours section', function()
+      local lines = {
+        '<<<<<<< HEAD',
+        '=======',
+        'local x = 2',
+        '>>>>>>> feature',
+      }
+      local regions = conflict.parse(lines)
+      assert.are.equal(1, #regions)
+      assert.are.equal(1, regions[1].ours_start)
+      assert.are.equal(1, regions[1].ours_end)
+    end)
+
+    it('handles empty theirs section', function()
+      local lines = {
+        '<<<<<<< HEAD',
+        'local x = 1',
+        '=======',
+        '>>>>>>> feature',
+      }
+      local regions = conflict.parse(lines)
+      assert.are.equal(1, #regions)
+      assert.are.equal(3, regions[1].theirs_start)
+      assert.are.equal(3, regions[1].theirs_end)
+    end)
+
+    it('returns empty for no markers', function()
+      local lines = { 'local x = 1', 'local y = 2' }
+      local regions = conflict.parse(lines)
+      assert.are.equal(0, #regions)
+    end)
+
+    it('discards malformed markers (no separator)', function()
+      local lines = {
+        '<<<<<<< HEAD',
+        'local x = 1',
+        '>>>>>>> feature',
+      }
+      local regions = conflict.parse(lines)
+      assert.are.equal(0, #regions)
+    end)
+
+    it('discards malformed markers (no end)', function()
+      local lines = {
+        '<<<<<<< HEAD',
+        'local x = 1',
+        '=======',
+        'local x = 2',
+      }
+      local regions = conflict.parse(lines)
+      assert.are.equal(0, #regions)
+    end)
+
+    it('handles trailing text on marker lines', function()
+      local lines = {
+        '<<<<<<< HEAD (some text)',
+        'local x = 1',
+        '======= extra',
+        'local x = 2',
+        '>>>>>>> feature-branch/some-thing',
+      }
+      local regions = conflict.parse(lines)
+      assert.are.equal(1, #regions)
+    end)
+
+    it('handles empty base in diff3', function()
+      local lines = {
+        '<<<<<<< HEAD',
+        'local x = 1',
+        '||||||| base',
+        '=======',
+        'local x = 2',
+        '>>>>>>> feature',
+      }
+      local regions = conflict.parse(lines)
+      assert.are.equal(1, #regions)
+      assert.are.equal(3, regions[1].base_start)
+      assert.are.equal(3, regions[1].base_end)
+    end)
+  end)
+
+  describe('highlighting', function()
+    after_each(function()
+      conflict.detach(vim.api.nvim_get_current_buf())
+    end)
+
+    it('applies extmarks for conflict regions', function()
+      local bufnr = create_file_buffer({
+        '<<<<<<< HEAD',
+        'local x = 1',
+        '=======',
+        'local x = 2',
+        '>>>>>>> feature',
+      })
+
+      conflict.attach(bufnr, default_config())
+
+      local extmarks = get_extmarks(bufnr)
+      assert.is_true(#extmarks > 0)
+
+      local has_ours = false
+      local has_theirs = false
+      local has_marker = false
+      for _, mark in ipairs(extmarks) do
+        local hl = mark[4] and mark[4].hl_group
+        if hl == 'DiffsConflictOurs' then
+          has_ours = true
+        end
+        if hl == 'DiffsConflictTheirs' then
+          has_theirs = true
+        end
+        if hl == 'DiffsConflictMarker' then
+          has_marker = true
+        end
+      end
+      assert.is_true(has_ours)
+      assert.is_true(has_theirs)
+      assert.is_true(has_marker)
+
+      helpers.delete_buffer(bufnr)
+    end)
+
+    it('applies virtual text when enabled', function()
+      local bufnr = create_file_buffer({
+        '<<<<<<< HEAD',
+        'local x = 1',
+        '=======',
+        'local x = 2',
+        '>>>>>>> feature',
+      })
+
+      conflict.attach(bufnr, default_config({ show_virtual_text = true }))
+
+      local extmarks = get_extmarks(bufnr)
+      local virt_text_count = 0
+      for _, mark in ipairs(extmarks) do
+        if mark[4] and mark[4].virt_text then
+          virt_text_count = virt_text_count + 1
+        end
+      end
+      assert.are.equal(2, virt_text_count)
+
+      helpers.delete_buffer(bufnr)
+    end)
+
+    it('does not apply virtual text when disabled', function()
+      local bufnr = create_file_buffer({
+        '<<<<<<< HEAD',
+        'local x = 1',
+        '=======',
+        'local x = 2',
+        '>>>>>>> feature',
+      })
+
+      conflict.attach(bufnr, default_config({ show_virtual_text = false }))
+
+      local extmarks = get_extmarks(bufnr)
+      local virt_text_count = 0
+      for _, mark in ipairs(extmarks) do
+        if mark[4] and mark[4].virt_text then
+          virt_text_count = virt_text_count + 1
+        end
+      end
+      assert.are.equal(0, virt_text_count)
+
+      helpers.delete_buffer(bufnr)
+    end)
+
+    it('applies number_hl_group to content lines', function()
+      local bufnr = create_file_buffer({
+        '<<<<<<< HEAD',
+        'local x = 1',
+        '=======',
+        'local x = 2',
+        '>>>>>>> feature',
+      })
+
+      conflict.attach(bufnr, default_config())
+
+      local extmarks = get_extmarks(bufnr)
+      local has_ours_nr = false
+      local has_theirs_nr = false
+      for _, mark in ipairs(extmarks) do
+        local nr = mark[4] and mark[4].number_hl_group
+        if nr == 'DiffsConflictOursNr' then
+          has_ours_nr = true
+        end
+        if nr == 'DiffsConflictTheirsNr' then
+          has_theirs_nr = true
+        end
+      end
+      assert.is_true(has_ours_nr)
+      assert.is_true(has_theirs_nr)
+
+      helpers.delete_buffer(bufnr)
+    end)
+
+    it('highlights base region in diff3', function()
+      local bufnr = create_file_buffer({
+        '<<<<<<< HEAD',
+        'local x = 1',
+        '||||||| base',
+        'local x = 0',
+        '=======',
+        'local x = 2',
+        '>>>>>>> feature',
+      })
+
+      conflict.attach(bufnr, default_config())
+
+      local extmarks = get_extmarks(bufnr)
+      local has_base = false
+      for _, mark in ipairs(extmarks) do
+        if mark[4] and mark[4].hl_group == 'DiffsConflictBase' then
+          has_base = true
+          break
+        end
+      end
+      assert.is_true(has_base)
+
+      helpers.delete_buffer(bufnr)
+    end)
+
+    it('clears extmarks on detach', function()
+      local bufnr = create_file_buffer({
+        '<<<<<<< HEAD',
+        'local x = 1',
+        '=======',
+        'local x = 2',
+        '>>>>>>> feature',
+      })
+
+      conflict.attach(bufnr, default_config())
+      assert.is_true(#get_extmarks(bufnr) > 0)
+
+      conflict.detach(bufnr)
+      assert.are.equal(0, #get_extmarks(bufnr))
+
+      helpers.delete_buffer(bufnr)
+    end)
+  end)
+
+  describe('resolution', function()
+    local function make_conflict_buffer()
+      local bufnr = create_file_buffer({
+        '<<<<<<< HEAD',
+        'local x = 1',
+        '=======',
+        'local x = 2',
+        '>>>>>>> feature',
+      })
+      vim.api.nvim_set_current_buf(bufnr)
+      return bufnr
+    end
+
+    it('resolve_ours keeps ours content', function()
+      local bufnr = make_conflict_buffer()
+      vim.api.nvim_win_set_cursor(0, { 2, 0 })
+
+      conflict.resolve_ours(bufnr, default_config())
+
+      local lines = vim.api.nvim_buf_get_lines(bufnr, 0, -1, false)
+      assert.are.equal(1, #lines)
+      assert.are.equal('local x = 1', lines[1])
+
+      helpers.delete_buffer(bufnr)
+    end)
+
+    it('resolve_theirs keeps theirs content', function()
+      local bufnr = make_conflict_buffer()
+      vim.api.nvim_win_set_cursor(0, { 2, 0 })
+
+      conflict.resolve_theirs(bufnr, default_config())
+
+      local lines = vim.api.nvim_buf_get_lines(bufnr, 0, -1, false)
+      assert.are.equal(1, #lines)
+      assert.are.equal('local x = 2', lines[1])
+
+      helpers.delete_buffer(bufnr)
+    end)
+
+    it('resolve_both keeps ours then theirs', function()
+      local bufnr = make_conflict_buffer()
+      vim.api.nvim_win_set_cursor(0, { 2, 0 })
+
+      conflict.resolve_both(bufnr, default_config())
+
+      local lines = vim.api.nvim_buf_get_lines(bufnr, 0, -1, false)
+      assert.are.equal(2, #lines)
+      assert.are.equal('local x = 1', lines[1])
+      assert.are.equal('local x = 2', lines[2])
+
+      helpers.delete_buffer(bufnr)
+    end)
+
+    it('resolve_none removes entire block', function()
+      local bufnr = make_conflict_buffer()
+      vim.api.nvim_win_set_cursor(0, { 2, 0 })
+
+      conflict.resolve_none(bufnr, default_config())
+
+      local lines = vim.api.nvim_buf_get_lines(bufnr, 0, -1, false)
+      assert.are.equal(1, #lines)
+      assert.are.equal('', lines[1])
+
+      helpers.delete_buffer(bufnr)
+    end)
+
+    it('does nothing when cursor is outside conflict', function()
+      local bufnr = create_file_buffer({
+        'normal line',
+        '<<<<<<< HEAD',
+        'local x = 1',
+        '=======',
+        'local x = 2',
+        '>>>>>>> feature',
+      })
+      vim.api.nvim_set_current_buf(bufnr)
+      vim.api.nvim_win_set_cursor(0, { 1, 0 })
+
+      conflict.resolve_ours(bufnr, default_config())
+
+      local lines = vim.api.nvim_buf_get_lines(bufnr, 0, -1, false)
+      assert.are.equal(6, #lines)
+
+      helpers.delete_buffer(bufnr)
+    end)
+
+    it('resolves one conflict among multiple', function()
+      local bufnr = create_file_buffer({
+        '<<<<<<< HEAD',
+        'a',
+        '=======',
+        'b',
+        '>>>>>>> feat',
+        'middle',
+        '<<<<<<< HEAD',
+        'c',
+        '=======',
+        'd',
+        '>>>>>>> feat',
+      })
+      vim.api.nvim_set_current_buf(bufnr)
+      vim.api.nvim_win_set_cursor(0, { 2, 0 })
+
+      conflict.resolve_ours(bufnr, default_config())
+
+      local lines = vim.api.nvim_buf_get_lines(bufnr, 0, -1, false)
+      assert.are.equal('a', lines[1])
+      assert.are.equal('middle', lines[2])
+      assert.are.equal('<<<<<<< HEAD', lines[3])
+
+      helpers.delete_buffer(bufnr)
+    end)
+
+    it('resolve_ours with empty ours section', function()
+      local bufnr = create_file_buffer({
+        '<<<<<<< HEAD',
+        '=======',
+        'local x = 2',
+        '>>>>>>> feature',
+      })
+      vim.api.nvim_set_current_buf(bufnr)
+      vim.api.nvim_win_set_cursor(0, { 1, 0 })
+
+      conflict.resolve_ours(bufnr, default_config())
+
+      local lines = vim.api.nvim_buf_get_lines(bufnr, 0, -1, false)
+      assert.are.equal(1, #lines)
+      assert.are.equal('', lines[1])
+
+      helpers.delete_buffer(bufnr)
+    end)
+
+    it('handles diff3 resolution (ignores base)', function()
+      local bufnr = create_file_buffer({
+        '<<<<<<< HEAD',
+        'local x = 1',
+        '||||||| base',
+        'local x = 0',
+        '=======',
+        'local x = 2',
+        '>>>>>>> feature',
+      })
+      vim.api.nvim_set_current_buf(bufnr)
+      vim.api.nvim_win_set_cursor(0, { 2, 0 })
+
+      conflict.resolve_theirs(bufnr, default_config())
+
+      local lines = vim.api.nvim_buf_get_lines(bufnr, 0, -1, false)
+      assert.are.equal(1, #lines)
+      assert.are.equal('local x = 2', lines[1])
+
+      helpers.delete_buffer(bufnr)
+    end)
+  end)
+
+  describe('navigation', function()
+    it('goto_next jumps to next conflict', function()
+      local bufnr = create_file_buffer({
+        'normal',
+        '<<<<<<< HEAD',
+        'a',
+        '=======',
+        'b',
+        '>>>>>>> feat',
+        'middle',
+        '<<<<<<< HEAD',
+        'c',
+        '=======',
+        'd',
+        '>>>>>>> feat',
+      })
+      vim.api.nvim_set_current_buf(bufnr)
+      vim.api.nvim_win_set_cursor(0, { 1, 0 })
+
+      conflict.goto_next(bufnr)
+      assert.are.equal(2, vim.api.nvim_win_get_cursor(0)[1])
+
+      conflict.goto_next(bufnr)
+      assert.are.equal(8, vim.api.nvim_win_get_cursor(0)[1])
+
+      helpers.delete_buffer(bufnr)
+    end)
+
+    it('goto_next wraps to first conflict', function()
+      local bufnr = create_file_buffer({
+        '<<<<<<< HEAD',
+        'a',
+        '=======',
+        'b',
+        '>>>>>>> feat',
+      })
+      vim.api.nvim_set_current_buf(bufnr)
+      vim.api.nvim_win_set_cursor(0, { 5, 0 })
+
+      conflict.goto_next(bufnr)
+      assert.are.equal(1, vim.api.nvim_win_get_cursor(0)[1])
+
+      helpers.delete_buffer(bufnr)
+    end)
+
+    it('goto_prev jumps to previous conflict', function()
+      local bufnr = create_file_buffer({
+        '<<<<<<< HEAD',
+        'a',
+        '=======',
+        'b',
+        '>>>>>>> feat',
+        'middle',
+        '<<<<<<< HEAD',
+        'c',
+        '=======',
+        'd',
+        '>>>>>>> feat',
+        'end',
+      })
+      vim.api.nvim_set_current_buf(bufnr)
+      vim.api.nvim_win_set_cursor(0, { 12, 0 })
+
+      conflict.goto_prev(bufnr)
+      assert.are.equal(7, vim.api.nvim_win_get_cursor(0)[1])
+
+      conflict.goto_prev(bufnr)
+      assert.are.equal(1, vim.api.nvim_win_get_cursor(0)[1])
+
+      helpers.delete_buffer(bufnr)
+    end)
+
+    it('goto_prev wraps to last conflict', function()
+      local bufnr = create_file_buffer({
+        '<<<<<<< HEAD',
+        'a',
+        '=======',
+        'b',
+        '>>>>>>> feat',
+      })
+      vim.api.nvim_set_current_buf(bufnr)
+      vim.api.nvim_win_set_cursor(0, { 1, 0 })
+
+      conflict.goto_prev(bufnr)
+      assert.are.equal(1, vim.api.nvim_win_get_cursor(0)[1])
+
+      helpers.delete_buffer(bufnr)
+    end)
+
+    it('goto_next does nothing with no conflicts', function()
+      local bufnr = create_file_buffer({ 'normal line' })
+      vim.api.nvim_set_current_buf(bufnr)
+      vim.api.nvim_win_set_cursor(0, { 1, 0 })
+
+      conflict.goto_next(bufnr)
+      assert.are.equal(1, vim.api.nvim_win_get_cursor(0)[1])
+
+      helpers.delete_buffer(bufnr)
+    end)
+  end)
+
+  describe('lifecycle', function()
+    it('attach is idempotent', function()
+      local bufnr = create_file_buffer({
+        '<<<<<<< HEAD',
+        'a',
+        '=======',
+        'b',
+        '>>>>>>> feat',
+      })
+      local cfg = default_config()
+      conflict.attach(bufnr, cfg)
+      local count1 = #get_extmarks(bufnr)
+      conflict.attach(bufnr, cfg)
+      local count2 = #get_extmarks(bufnr)
+      assert.are.equal(count1, count2)
+      conflict.detach(bufnr)
+      helpers.delete_buffer(bufnr)
+    end)
+
+    it('skips non-file buffers', function()
+      local bufnr = helpers.create_buffer({
+        '<<<<<<< HEAD',
+        'a',
+        '=======',
+        'b',
+        '>>>>>>> feat',
+      })
+      vim.api.nvim_set_option_value('buftype', 'nofile', { buf = bufnr })
+
+      conflict.attach(bufnr, default_config())
+      assert.are.equal(0, #get_extmarks(bufnr))
+
+      helpers.delete_buffer(bufnr)
+    end)
+
+    it('skips buffers without conflict markers', function()
+      local bufnr = create_file_buffer({ 'local x = 1', 'local y = 2' })
+
+      conflict.attach(bufnr, default_config())
+      assert.are.equal(0, #get_extmarks(bufnr))
+
+      helpers.delete_buffer(bufnr)
+    end)
+
+    it('re-highlights when markers return after resolution', function()
+      local bufnr = create_file_buffer({
+        '<<<<<<< HEAD',
+        'local x = 1',
+        '=======',
+        'local x = 2',
+        '>>>>>>> feature',
+      })
+      vim.api.nvim_set_current_buf(bufnr)
+      local cfg = default_config()
+      conflict.attach(bufnr, cfg)
+
+      assert.is_true(#get_extmarks(bufnr) > 0)
+
+      vim.api.nvim_win_set_cursor(0, { 2, 0 })
+      conflict.resolve_ours(bufnr, cfg)
+      assert.are.equal(0, #get_extmarks(bufnr))
+
+      vim.api.nvim_buf_set_lines(bufnr, 0, -1, false, {
+        '<<<<<<< HEAD',
+        'local x = 1',
+        '=======',
+        'local x = 2',
+        '>>>>>>> feature',
+      })
+      vim.api.nvim_exec_autocmds('TextChanged', { buffer = bufnr })
+
+      assert.is_true(#get_extmarks(bufnr) > 0)
+
+      conflict.detach(bufnr)
+      helpers.delete_buffer(bufnr)
+    end)
+
+    it('detaches after last conflict resolved', function()
+      local bufnr = create_file_buffer({
+        '<<<<<<< HEAD',
+        'local x = 1',
+        '=======',
+        'local x = 2',
+        '>>>>>>> feature',
+      })
+      vim.api.nvim_set_current_buf(bufnr)
+      conflict.attach(bufnr, default_config())
+
+      assert.is_true(#get_extmarks(bufnr) > 0)
+
+      vim.api.nvim_win_set_cursor(0, { 2, 0 })
+      conflict.resolve_ours(bufnr, default_config())
+
+      assert.are.equal(0, #get_extmarks(bufnr))
+
+      helpers.delete_buffer(bufnr)
+    end)
+  end)
+end)

spec/diff_spec.lua

@@ -0,0 +1,163 @@
+require('spec.helpers')
+local diff = require('diffs.diff')
+
+describe('diff', function()
+  describe('extract_change_groups', function()
+    it('returns empty for all context lines', function()
+      local groups = diff.extract_change_groups({ ' line1', ' line2', ' line3' })
+      assert.are.equal(0, #groups)
+    end)
+
+    it('returns empty for pure additions', function()
+      local groups = diff.extract_change_groups({ '+line1', '+line2' })
+      assert.are.equal(0, #groups)
+    end)
+
+    it('returns empty for pure deletions', function()
+      local groups = diff.extract_change_groups({ '-line1', '-line2' })
+      assert.are.equal(0, #groups)
+    end)
+
+    it('extracts single change group', function()
+      local groups = diff.extract_change_groups({
+        ' context',
+        '-old line',
+        '+new line',
+        ' context',
+      })
+      assert.are.equal(1, #groups)
+      assert.are.equal(1, #groups[1].del_lines)
+      assert.are.equal(1, #groups[1].add_lines)
+      assert.are.equal('old line', groups[1].del_lines[1].text)
+      assert.are.equal('new line', groups[1].add_lines[1].text)
+    end)
+
+    it('extracts multiple change groups separated by context', function()
+      local groups = diff.extract_change_groups({
+        '-old1',
+        '+new1',
+        ' context',
+        '-old2',
+        '+new2',
+      })
+      assert.are.equal(2, #groups)
+      assert.are.equal('old1', groups[1].del_lines[1].text)
+      assert.are.equal('new1', groups[1].add_lines[1].text)
+      assert.are.equal('old2', groups[2].del_lines[1].text)
+      assert.are.equal('new2', groups[2].add_lines[1].text)
+    end)
+
+    it('tracks correct line indices', function()
+      local groups = diff.extract_change_groups({
+        ' context',
+        '-deleted',
+        '+added',
+      })
+      assert.are.equal(2, groups[1].del_lines[1].idx)
+      assert.are.equal(3, groups[1].add_lines[1].idx)
+    end)
+
+    it('handles multiple del lines followed by multiple add lines', function()
+      local groups = diff.extract_change_groups({
+        '-del1',
+        '-del2',
+        '+add1',
+        '+add2',
+        '+add3',
+      })
+      assert.are.equal(1, #groups)
+      assert.are.equal(2, #groups[1].del_lines)
+      assert.are.equal(3, #groups[1].add_lines)
+    end)
+  end)
+
+  describe('compute_intra_hunks', function()
+    it('returns nil for all-addition hunks', function()
+      local result = diff.compute_intra_hunks({ '+line1', '+line2' }, 'default')
+      assert.is_nil(result)
+    end)
+
+    it('returns nil for all-deletion hunks', function()
+      local result = diff.compute_intra_hunks({ '-line1', '-line2' }, 'default')
+      assert.is_nil(result)
+    end)
+
+    it('returns nil for context-only hunks', function()
+      local result = diff.compute_intra_hunks({ ' line1', ' line2' }, 'default')
+      assert.is_nil(result)
+    end)
+
+    it('returns spans for single word change', function()
+      local result = diff.compute_intra_hunks({
+        '-local x = 1',
+        '+local x = 2',
+      }, 'default')
+      assert.is_not_nil(result)
+      assert.is_true(#result.del_spans > 0)
+      assert.is_true(#result.add_spans > 0)
+    end)
+
+    it('identifies correct byte offsets for word change', function()
+      local result = diff.compute_intra_hunks({
+        '-local x = 1',
+        '+local x = 2',
+      }, 'default')
+      assert.is_not_nil(result)
+
+      assert.are.equal(1, #result.del_spans)
+      assert.are.equal(1, #result.add_spans)
+      local del_span = result.del_spans[1]
+      local add_span = result.add_spans[1]
+      local del_text = ('local x = 1'):sub(del_span.col_start, del_span.col_end - 1)
+      local add_text = ('local x = 2'):sub(add_span.col_start, add_span.col_end - 1)
+      assert.are.equal('1', del_text)
+      assert.are.equal('2', add_text)
+    end)
+
+    it('handles multiple change groups separated by context', function()
+      local result = diff.compute_intra_hunks({
+        '-local a = 1',
+        '+local a = 2',
+        ' local b = 3',
+        '-local c = 4',
+        '+local c = 5',
+      }, 'default')
+      assert.is_not_nil(result)
+      assert.is_true(#result.del_spans >= 2)
+      assert.is_true(#result.add_spans >= 2)
+    end)
+
+    it('handles uneven line counts (2 old, 1 new)', function()
+      local result = diff.compute_intra_hunks({
+        '-line one',
+        '-line two',
+        '+line combined',
+      }, 'default')
+      assert.is_not_nil(result)
+    end)
+
+    it('handles multi-byte UTF-8 content', function()
+      local result = diff.compute_intra_hunks({
+        '-local x = "héllo"',
+        '+local x = "wörld"',
+      }, 'default')
+      assert.is_not_nil(result)
+      assert.is_true(#result.del_spans > 0)
+      assert.is_true(#result.add_spans > 0)
+    end)
+
+    it('returns nil when del and add are identical', function()
+      local result = diff.compute_intra_hunks({
+        '-local x = 1',
+        '+local x = 1',
+      }, 'default')
+      assert.is_nil(result)
+    end)
+  end)
+
+  describe('has_vscode', function()
+    it('returns false in test environment', function()
+      assert.is_false(diff.has_vscode())
+    end)
+  end)
+end)

spec/helpers.lua

@@ -2,6 +2,8 @@ local plugin_dir = vim.fn.getcwd()
 vim.opt.runtimepath:prepend(plugin_dir)
 vim.opt.packpath = {}
 
+vim.cmd('filetype on')
+
 local function ensure_parser(lang)
   local ok = pcall(vim.treesitter.language.inspect, lang)
   if not ok then
@@ -10,6 +12,7 @@ local function ensure_parser(lang)
 end
 
 ensure_parser('lua')
+ensure_parser('vim')
 
 local M = {}
 

spec/highlight_spec.lua

@@ -7,8 +7,10 @@ describe('highlight', function()
 
     before_each(function()
       ns = vim.api.nvim_create_namespace('diffs_test')
+      local normal = vim.api.nvim_get_hl(0, { name = 'Normal' })
       local diff_add = vim.api.nvim_get_hl(0, { name = 'DiffAdd' })
       local diff_delete = vim.api.nvim_get_hl(0, { name = 'DiffDelete' })
+      vim.api.nvim_set_hl(0, 'DiffsClear', { fg = normal.fg or 0xc0c0c0 })
       vim.api.nvim_set_hl(0, 'DiffsAdd', { bg = diff_add.bg })
       vim.api.nvim_set_hl(0, 'DiffsDelete', { bg = diff_delete.bg })
     end)
@@ -35,6 +37,7 @@ describe('highlight', function()
         highlights = {
           background = false,
           gutter = false,
+          context = { enabled = false, lines = 0 },
           treesitter = {
             enabled = true,
             max_lines = 500,
@@ -43,6 +46,11 @@ describe('highlight', function()
             enabled = false,
             max_lines = 200,
           },
+          intra = {
+            enabled = false,
+            algorithm = 'default',
+            max_lines = 500,
+          },
         },
       }
       if overrides then
@@ -77,7 +85,7 @@ describe('highlight', function()
       delete_buffer(bufnr)
     end)
 
-    it('applies Normal extmarks to clear diff colors', function()
+    it('applies DiffsClear extmarks to clear diff colors', function()
       local bufnr = create_buffer({
         '@@ -1,1 +1,2 @@',
         ' local x = 1',
@@ -94,14 +102,46 @@ describe('highlight', function()
       highlight.highlight_hunk(bufnr, ns, hunk, default_opts())
 
       local extmarks = get_extmarks(bufnr)
-      local has_normal = false
+      local has_clear = false
       for _, mark in ipairs(extmarks) do
-        if mark[4] and mark[4].hl_group == 'Normal' then
-          has_normal = true
+        if mark[4] and mark[4].hl_group == 'DiffsClear' then
+          has_clear = true
           break
         end
       end
-      assert.is_true(has_normal)
+      assert.is_true(has_clear)
+      delete_buffer(bufnr)
+    end)
+
+    it('produces treesitter captures on all lines with split parsing', function()
+      local bufnr = create_buffer({
+        '@@ -1,3 +1,3 @@',
+        ' local x = 1',
+        '-local y = 2',
+        '+local y = 3',
+        ' return x',
+      })
+
+      local hunk = {
+        filename = 'test.lua',
+        lang = 'lua',
+        start_line = 1,
+        lines = { ' local x = 1', '-local y = 2', '+local y = 3', ' return x' },
+      }
+
+      highlight.highlight_hunk(bufnr, ns, hunk, default_opts())
+
+      local extmarks = get_extmarks(bufnr)
+      local lines_with_ts = {}
+      for _, mark in ipairs(extmarks) do
+        if mark[4] and mark[4].hl_group and mark[4].hl_group:match('^@.*%.lua$') then
+          lines_with_ts[mark[2]] = true
+        end
+      end
+      assert.is_true(lines_with_ts[1] ~= nil)
+      assert.is_true(lines_with_ts[2] ~= nil)
+      assert.is_true(lines_with_ts[3] ~= nil)
+      assert.is_true(lines_with_ts[4] ~= nil)
       delete_buffer(bufnr)
     end)
 
@@ -180,6 +220,40 @@ describe('highlight', function()
       delete_buffer(bufnr)
     end)
 
+    it('highlights function keyword in header context', function()
+      local bufnr = create_buffer({
+        '@@ -5,3 +5,4 @@ function M.setup()',
+        ' local x = 1',
+        '+local y = 2',
+        ' return x',
+      })
+
+      local hunk = {
+        filename = 'test.lua',
+        lang = 'lua',
+        start_line = 1,
+        header_context = 'function M.setup()',
+        header_context_col = 18,
+        lines = { ' local x = 1', '+local y = 2', ' return x' },
+      }
+
+      highlight.highlight_hunk(bufnr, ns, hunk, default_opts())
+
+      local extmarks = get_extmarks(bufnr)
+      local has_keyword_function = false
+      for _, mark in ipairs(extmarks) do
+        if mark[2] == 0 and mark[4] and mark[4].hl_group then
+          local hl = mark[4].hl_group
+          if hl == '@keyword.function.lua' or hl == '@keyword.lua' then
+            has_keyword_function = true
+            break
+          end
+        end
+      end
+      assert.is_true(has_keyword_function)
+      delete_buffer(bufnr)
+    end)
+
     it('does not highlight header when no header_context', function()
       local bufnr = create_buffer({
         '@@ -10,3 +10,4 @@',
@@ -322,7 +396,7 @@ describe('highlight', function()
       local extmarks = get_extmarks(bufnr)
       local has_diff_add = false
       for _, mark in ipairs(extmarks) do
-        if mark[4] and mark[4].line_hl_group == 'DiffsAdd' then
+        if mark[4] and mark[4].hl_group == 'DiffsAdd' then
           has_diff_add = true
           break
         end
@@ -355,7 +429,7 @@ describe('highlight', function()
       local extmarks = get_extmarks(bufnr)
       local has_diff_delete = false
       for _, mark in ipairs(extmarks) do
-        if mark[4] and mark[4].line_hl_group == 'DiffsDelete' then
+        if mark[4] and mark[4].hl_group == 'DiffsDelete' then
           has_diff_delete = true
           break
         end
@@ -388,7 +462,7 @@ describe('highlight', function()
       local extmarks = get_extmarks(bufnr)
       local has_line_hl = false
       for _, mark in ipairs(extmarks) do
-        if mark[4] and mark[4].line_hl_group then
+        if mark[4] and (mark[4].hl_group == 'DiffsAdd' or mark[4].hl_group == 'DiffsDelete') then
           has_line_hl = true
           break
         end
@@ -520,7 +594,7 @@ describe('highlight', function()
       local extmarks = get_extmarks(bufnr)
       local has_diff_add = false
       for _, mark in ipairs(extmarks) do
-        if mark[4] and mark[4].line_hl_group == 'DiffsAdd' then
+        if mark[4] and mark[4].hl_group == 'DiffsAdd' then
           has_diff_add = true
           break
         end
@@ -571,7 +645,7 @@ describe('highlight', function()
       local extmarks = get_extmarks(bufnr)
       local has_syntax_hl = false
       for _, mark in ipairs(extmarks) do
-        if mark[4] and mark[4].hl_group and mark[4].hl_group ~= 'Normal' then
+        if mark[4] and mark[4].hl_group and mark[4].hl_group ~= 'DiffsClear' then
           has_syntax_hl = true
           break
         end
@@ -605,7 +679,7 @@ describe('highlight', function()
       local extmarks = get_extmarks(bufnr)
       local has_syntax_hl = false
       for _, mark in ipairs(extmarks) do
-        if mark[4] and mark[4].hl_group and mark[4].hl_group ~= 'Normal' then
+        if mark[4] and mark[4].hl_group and mark[4].hl_group ~= 'DiffsClear' then
           has_syntax_hl = true
           break
         end
@@ -668,7 +742,7 @@ describe('highlight', function()
       local extmarks = get_extmarks(bufnr)
       local has_diff_add = false
       for _, mark in ipairs(extmarks) do
-        if mark[4] and mark[4].line_hl_group == 'DiffsAdd' then
+        if mark[4] and mark[4].hl_group == 'DiffsAdd' then
           has_diff_add = true
           break
         end
@@ -677,7 +751,7 @@ describe('highlight', function()
       delete_buffer(bufnr)
     end)
 
-    it('applies Normal blanking for vim fallback hunks', function()
+    it('applies DiffsClear blanking for vim fallback hunks', function()
       local orig_synID = vim.fn.synID
       local orig_synIDtrans = vim.fn.synIDtrans
       local orig_synIDattr = vim.fn.synIDattr
@@ -717,14 +791,565 @@ describe('highlight', function()
       vim.fn.synIDattr = orig_synIDattr
 
       local extmarks = get_extmarks(bufnr)
-      local has_normal = false
+      local has_clear = false
       for _, mark in ipairs(extmarks) do
-        if mark[4] and mark[4].hl_group == 'Normal' then
-          has_normal = true
+        if mark[4] and mark[4].hl_group == 'DiffsClear' then
+          has_clear = true
           break
         end
       end
-      assert.is_true(has_normal)
+      assert.is_true(has_clear)
+      delete_buffer(bufnr)
+    end)
+
+    it('uses hl_group not line_hl_group for line backgrounds', function()
+      local bufnr = create_buffer({
+        '@@ -1,2 +1,1 @@',
+        '-local x = 1',
+        '+local y = 2',
+      })
+
+      local hunk = {
+        filename = 'test.lua',
+        lang = 'lua',
+        start_line = 1,
+        lines = { '-local x = 1', '+local y = 2' },
+      }
+
+      highlight.highlight_hunk(
+        bufnr,
+        ns,
+        hunk,
+        default_opts({ highlights = { background = true } })
+      )
+
+      local extmarks = get_extmarks(bufnr)
+      for _, mark in ipairs(extmarks) do
+        local d = mark[4]
+        if d and (d.hl_group == 'DiffsAdd' or d.hl_group == 'DiffsDelete') then
+          assert.is_true(d.hl_eol == true)
+          assert.is_nil(d.line_hl_group)
+        end
+      end
+      delete_buffer(bufnr)
+    end)
+
+    it('hl_eol background extmarks are multiline so hl_eol takes effect', function()
+      local bufnr = create_buffer({
+        '@@ -1,2 +1,1 @@',
+        '-local x = 1',
+        '+local y = 2',
+      })
+
+      local hunk = {
+        filename = 'test.lua',
+        lang = 'lua',
+        start_line = 1,
+        lines = { '-local x = 1', '+local y = 2' },
+      }
+
+      highlight.highlight_hunk(
+        bufnr,
+        ns,
+        hunk,
+        default_opts({ highlights = { background = true } })
+      )
+
+      local extmarks = get_extmarks(bufnr)
+      for _, mark in ipairs(extmarks) do
+        local d = mark[4]
+        if d and (d.hl_group == 'DiffsAdd' or d.hl_group == 'DiffsDelete') then
+          assert.is_true(d.end_row > mark[2])
+        end
+      end
+      delete_buffer(bufnr)
+    end)
+
+    it('number_hl_group does not bleed to adjacent lines', function()
+      local bufnr = create_buffer({
+        '@@ -1,3 +1,3 @@',
+        ' local a = 0',
+        '-local x = 1',
+        '+local y = 2',
+        ' local b = 3',
+      })
+
+      local hunk = {
+        filename = 'test.lua',
+        lang = 'lua',
+        start_line = 1,
+        lines = { ' local a = 0', '-local x = 1', '+local y = 2', ' local b = 3' },
+      }
+
+      highlight.highlight_hunk(
+        bufnr,
+        ns,
+        hunk,
+        default_opts({ highlights = { background = true, gutter = true } })
+      )
+
+      local extmarks = get_extmarks(bufnr)
+      for _, mark in ipairs(extmarks) do
+        local d = mark[4]
+        if d and d.number_hl_group then
+          local start_row = mark[2]
+          local end_row = d.end_row or start_row
+          assert.are.equal(start_row, end_row)
+        end
+      end
+      delete_buffer(bufnr)
+    end)
+
+    it('line bg priority > DiffsClear priority', function()
+      local bufnr = create_buffer({
+        '@@ -1,2 +1,1 @@',
+        '-local x = 1',
+        '+local y = 2',
+      })
+
+      local hunk = {
+        filename = 'test.lua',
+        lang = 'lua',
+        start_line = 1,
+        lines = { '-local x = 1', '+local y = 2' },
+      }
+
+      highlight.highlight_hunk(
+        bufnr,
+        ns,
+        hunk,
+        default_opts({ highlights = { background = true } })
+      )
+
+      local extmarks = get_extmarks(bufnr)
+      local clear_priority = nil
+      local line_bg_priority = nil
+      for _, mark in ipairs(extmarks) do
+        local d = mark[4]
+        if d and d.hl_group == 'DiffsClear' then
+          clear_priority = d.priority
+        end
+        if d and (d.hl_group == 'DiffsAdd' or d.hl_group == 'DiffsDelete') then
+          line_bg_priority = d.priority
+        end
+      end
+      assert.is_not_nil(clear_priority)
+      assert.is_not_nil(line_bg_priority)
+      assert.is_true(line_bg_priority > clear_priority)
+      delete_buffer(bufnr)
+    end)
+
+    it('char-level extmarks have higher priority than line bg', function()
+      vim.api.nvim_set_hl(0, 'DiffsAddText', { bg = 0x00FF00 })
+      vim.api.nvim_set_hl(0, 'DiffsDeleteText', { bg = 0xFF0000 })
+
+      local bufnr = create_buffer({
+        '@@ -1,2 +1,2 @@',
+        '-local x = 1',
+        '+local x = 2',
+      })
+
+      local hunk = {
+        filename = 'test.lua',
+        lang = 'lua',
+        start_line = 1,
+        lines = { '-local x = 1', '+local x = 2' },
+      }
+
+      highlight.highlight_hunk(
+        bufnr,
+        ns,
+        hunk,
+        default_opts({
+          highlights = {
+            background = true,
+            intra = { enabled = true, algorithm = 'default', max_lines = 500 },
+          },
+        })
+      )
+
+      local extmarks = get_extmarks(bufnr)
+      local line_bg_priority = nil
+      local char_bg_priority = nil
+      for _, mark in ipairs(extmarks) do
+        local d = mark[4]
+        if d and (d.hl_group == 'DiffsAdd' or d.hl_group == 'DiffsDelete') then
+          line_bg_priority = d.priority
+        end
+        if d and (d.hl_group == 'DiffsAddText' or d.hl_group == 'DiffsDeleteText') then
+          char_bg_priority = d.priority
+        end
+      end
+      assert.is_not_nil(line_bg_priority)
+      assert.is_not_nil(char_bg_priority)
+      assert.is_true(char_bg_priority > line_bg_priority)
+      delete_buffer(bufnr)
+    end)
+
+    it('creates char-level extmarks for changed characters', function()
+      vim.api.nvim_set_hl(0, 'DiffsAddText', { bg = 0x00FF00 })
+      vim.api.nvim_set_hl(0, 'DiffsDeleteText', { bg = 0xFF0000 })
+
+      local bufnr = create_buffer({
+        '@@ -1,2 +1,2 @@',
+        '-local x = 1',
+        '+local x = 2',
+      })
+
+      local hunk = {
+        filename = 'test.lua',
+        lang = 'lua',
+        start_line = 1,
+        lines = { '-local x = 1', '+local x = 2' },
+      }
+
+      highlight.highlight_hunk(
+        bufnr,
+        ns,
+        hunk,
+        default_opts({
+          highlights = { intra = { enabled = true, algorithm = 'default', max_lines = 500 } },
+        })
+      )
+
+      local extmarks = get_extmarks(bufnr)
+      local add_text_marks = {}
+      local del_text_marks = {}
+      for _, mark in ipairs(extmarks) do
+        local d = mark[4]
+        if d and d.hl_group == 'DiffsAddText' then
+          table.insert(add_text_marks, mark)
+        end
+        if d and d.hl_group == 'DiffsDeleteText' then
+          table.insert(del_text_marks, mark)
+        end
+      end
+      assert.is_true(#add_text_marks > 0)
+      assert.is_true(#del_text_marks > 0)
+      delete_buffer(bufnr)
+    end)
+
+    it('does not create char-level extmarks when intra disabled', function()
+      local bufnr = create_buffer({
+        '@@ -1,2 +1,2 @@',
+        '-local x = 1',
+        '+local x = 2',
+      })
+
+      local hunk = {
+        filename = 'test.lua',
+        lang = 'lua',
+        start_line = 1,
+        lines = { '-local x = 1', '+local x = 2' },
+      }
+
+      highlight.highlight_hunk(
+        bufnr,
+        ns,
+        hunk,
+        default_opts({
+          highlights = { intra = { enabled = false, algorithm = 'default', max_lines = 500 } },
+        })
+      )
+
+      local extmarks = get_extmarks(bufnr)
+      for _, mark in ipairs(extmarks) do
+        local d = mark[4]
+        assert.is_not_equal('DiffsAddText', d and d.hl_group)
+        assert.is_not_equal('DiffsDeleteText', d and d.hl_group)
+      end
+      delete_buffer(bufnr)
+    end)
+
+    it('does not create char-level extmarks for pure additions', function()
+      vim.api.nvim_set_hl(0, 'DiffsAddText', { bg = 0x00FF00 })
+
+      local bufnr = create_buffer({
+        '@@ -1,0 +1,2 @@',
+        '+local x = 1',
+        '+local y = 2',
+      })
+
+      local hunk = {
+        filename = 'test.lua',
+        lang = 'lua',
+        start_line = 1,
+        lines = { '+local x = 1', '+local y = 2' },
+      }
+
+      highlight.highlight_hunk(
+        bufnr,
+        ns,
+        hunk,
+        default_opts({
+          highlights = { intra = { enabled = true, algorithm = 'default', max_lines = 500 } },
+        })
+      )
+
+      local extmarks = get_extmarks(bufnr)
+      for _, mark in ipairs(extmarks) do
+        local d = mark[4]
+        assert.is_not_equal('DiffsAddText', d and d.hl_group)
+        assert.is_not_equal('DiffsDeleteText', d and d.hl_group)
+      end
+      delete_buffer(bufnr)
+    end)
+
+    it('enforces priority order: DiffsClear < syntax < line bg < char bg', function()
+      vim.api.nvim_set_hl(0, 'DiffsAddText', { bg = 0x00FF00 })
+      vim.api.nvim_set_hl(0, 'DiffsDeleteText', { bg = 0xFF0000 })
+
+      local bufnr = create_buffer({
+        '@@ -1,2 +1,2 @@',
+        '-local x = 1',
+        '+local x = 2',
+      })
+
+      local hunk = {
+        filename = 'test.lua',
+        lang = 'lua',
+        start_line = 1,
+        lines = { '-local x = 1', '+local x = 2' },
+      }
+
+      highlight.highlight_hunk(
+        bufnr,
+        ns,
+        hunk,
+        default_opts({
+          highlights = {
+            background = true,
+            intra = { enabled = true, algorithm = 'default', max_lines = 500 },
+          },
+        })
+      )
+
+      local extmarks = get_extmarks(bufnr)
+      local priorities = { clear = {}, line_bg = {}, syntax = {}, char_bg = {} }
+      for _, mark in ipairs(extmarks) do
+        local d = mark[4]
+        if d then
+          if d.hl_group == 'DiffsClear' then
+            table.insert(priorities.clear, d.priority)
+          elseif d.hl_group == 'DiffsAdd' or d.hl_group == 'DiffsDelete' then
+            table.insert(priorities.line_bg, d.priority)
+          elseif d.hl_group == 'DiffsAddText' or d.hl_group == 'DiffsDeleteText' then
+            table.insert(priorities.char_bg, d.priority)
+          elseif d.hl_group and d.hl_group:match('^@.*%.lua$') then
+            table.insert(priorities.syntax, d.priority)
+          end
+        end
+      end
+
+      assert.is_true(#priorities.clear > 0)
+      assert.is_true(#priorities.line_bg > 0)
+      assert.is_true(#priorities.syntax > 0)
+      assert.is_true(#priorities.char_bg > 0)
+
+      local max_clear = math.max(unpack(priorities.clear))
+      local min_line_bg = math.min(unpack(priorities.line_bg))
+      local min_syntax = math.min(unpack(priorities.syntax))
+      local min_char_bg = math.min(unpack(priorities.char_bg))
+
+      assert.is_true(max_clear < min_syntax)
+      assert.is_true(min_syntax < min_line_bg)
+      assert.is_true(min_line_bg < min_char_bg)
+      delete_buffer(bufnr)
+    end)
+
+    it('context padding produces no extmarks on padding lines', function()
+      local repo_root = '/tmp/diffs-test-context'
+      vim.fn.mkdir(repo_root, 'p')
+
+      local f = io.open(repo_root .. '/test.lua', 'w')
+      f:write('local M = {}\n')
+      f:write('function M.hello()\n')
+      f:write('  return "hi"\n')
+      f:write('end\n')
+      f:write('return M\n')
+      f:close()
+
+      local bufnr = create_buffer({
+        '@@ -3,1 +3,2 @@',
+        ' return "hi"',
+        '+"bye"',
+      })
+
+      local hunk = {
+        filename = 'test.lua',
+        lang = 'lua',
+        start_line = 1,
+        lines = { '  return "hi"', '+"bye"' },
+        file_old_start = 3,
+        file_old_count = 1,
+        file_new_start = 3,
+        file_new_count = 2,
+        repo_root = repo_root,
+      }
+
+      highlight.highlight_hunk(
+        bufnr,
+        ns,
+        hunk,
+        default_opts({ highlights = { context = { enabled = true, lines = 25 } } })
+      )
+
+      local extmarks = get_extmarks(bufnr)
+      for _, mark in ipairs(extmarks) do
+        local row = mark[2]
+        assert.is_true(row >= 1 and row <= 2)
+      end
+
+      delete_buffer(bufnr)
+      os.remove(repo_root .. '/test.lua')
+      vim.fn.delete(repo_root, 'rf')
+    end)
+
+    it('context disabled matches behavior without padding', function()
+      local bufnr = create_buffer({
+        '@@ -1,1 +1,2 @@',
+        ' local x = 1',
+        '+local y = 2',
+      })
+
+      local hunk = {
+        filename = 'test.lua',
+        lang = 'lua',
+        start_line = 1,
+        lines = { ' local x = 1', '+local y = 2' },
+        file_new_start = 1,
+        file_new_count = 2,
+        repo_root = '/nonexistent',
+      }
+
+      highlight.highlight_hunk(
+        bufnr,
+        ns,
+        hunk,
+        default_opts({ highlights = { context = { enabled = false, lines = 0 } } })
+      )
+
+      local extmarks = get_extmarks(bufnr)
+      assert.is_true(#extmarks > 0)
+      delete_buffer(bufnr)
+    end)
+
+    it('gracefully handles missing file for context padding', function()
+      local bufnr = create_buffer({
+        '@@ -1,1 +1,2 @@',
+        ' local x = 1',
+        '+local y = 2',
+      })
+
+      local hunk = {
+        filename = 'test.lua',
+        lang = 'lua',
+        start_line = 1,
+        lines = { ' local x = 1', '+local y = 2' },
+        file_new_start = 1,
+        file_new_count = 2,
+        repo_root = '/nonexistent/path',
+      }
+
+      assert.has_no.errors(function()
+        highlight.highlight_hunk(
+          bufnr,
+          ns,
+          hunk,
+          default_opts({ highlights = { context = { enabled = true, lines = 25 } } })
+        )
+      end)
+
+      local extmarks = get_extmarks(bufnr)
+      assert.is_true(#extmarks > 0)
+      delete_buffer(bufnr)
+    end)
+
+    it('highlights treesitter injections', function()
+      local bufnr = create_buffer({
+        '@@ -1,1 +1,2 @@',
+        ' local x = 1',
+        '+vim.cmd([[ echo 1 ]])',
+      })
+
+      local hunk = {
+        filename = 'test.lua',
+        lang = 'lua',
+        start_line = 1,
+        lines = { ' local x = 1', '+vim.cmd([[ echo 1 ]])' },
+      }
+
+      highlight.highlight_hunk(bufnr, ns, hunk, default_opts())
+
+      local extmarks = get_extmarks(bufnr)
+      local has_vim_capture = false
+      for _, mark in ipairs(extmarks) do
+        if mark[4] and mark[4].hl_group and mark[4].hl_group:match('^@.*%.vim$') then
+          has_vim_capture = true
+          break
+        end
+      end
+      assert.is_true(has_vim_capture)
+      delete_buffer(bufnr)
+    end)
+
+    it('includes captures from both base and injected languages', function()
+      local bufnr = create_buffer({
+        '@@ -1,1 +1,2 @@',
+        ' local x = 1',
+        '+vim.cmd([[ echo 1 ]])',
+      })
+
+      local hunk = {
+        filename = 'test.lua',
+        lang = 'lua',
+        start_line = 1,
+        lines = { ' local x = 1', '+vim.cmd([[ echo 1 ]])' },
+      }
+
+      highlight.highlight_hunk(bufnr, ns, hunk, default_opts())
+
+      local extmarks = get_extmarks(bufnr)
+      local has_lua = false
+      local has_vim = false
+      for _, mark in ipairs(extmarks) do
+        if mark[4] and mark[4].hl_group then
+          if mark[4].hl_group:match('^@.*%.lua$') then
+            has_lua = true
+          end
+          if mark[4].hl_group:match('^@.*%.vim$') then
+            has_vim = true
+          end
+        end
+      end
+      assert.is_true(has_lua)
+      assert.is_true(has_vim)
+      delete_buffer(bufnr)
+    end)
+
+    it('filters @spell and @nospell captures from injections', function()
+      local bufnr = create_buffer({
+        '@@ -1,1 +1,2 @@',
+        ' local x = 1',
+        '+vim.cmd([[ echo 1 ]])',
+      })
+
+      local hunk = {
+        filename = 'test.lua',
+        lang = 'lua',
+        start_line = 1,
+        lines = { ' local x = 1', '+vim.cmd([[ echo 1 ]])' },
+      }
+
+      highlight.highlight_hunk(bufnr, ns, hunk, default_opts())
+
+      local extmarks = get_extmarks(bufnr)
+      for _, mark in ipairs(extmarks) do
+        if mark[4] and mark[4].hl_group then
+          assert.is_falsy(mark[4].hl_group:match('@spell'))
+          assert.is_falsy(mark[4].hl_group:match('@nospell'))
+        end
+      end
       delete_buffer(bufnr)
     end)
   end)
@@ -758,6 +1383,7 @@ describe('highlight', function()
         highlights = {
           background = false,
           gutter = false,
+          context = { enabled = false, lines = 0 },
           treesitter = { enabled = true, max_lines = 500 },
           vim = { enabled = false, max_lines = 200 },
         },
@@ -914,13 +1540,14 @@ describe('highlight', function()
         highlights = {
           background = false,
           gutter = false,
+          context = { enabled = false, lines = 0 },
           treesitter = { enabled = true, max_lines = 500 },
           vim = { enabled = false, max_lines = 200 },
         },
       }
     end
 
-    it('uses priority 200 for code languages', function()
+    it('uses priority 199 for code languages', function()
       local bufnr = create_buffer({
         '@@ -1,1 +1,2 @@',
         ' local x = 1',
@@ -937,16 +1564,16 @@ describe('highlight', function()
       highlight.highlight_hunk(bufnr, ns, hunk, default_opts())
 
       local extmarks = get_extmarks(bufnr)
-      local has_priority_200 = false
+      local has_priority_199 = false
       for _, mark in ipairs(extmarks) do
         if mark[4] and mark[4].hl_group and mark[4].hl_group:match('^@.*%.lua$') then
-          if mark[4].priority == 200 then
-            has_priority_200 = true
+          if mark[4].priority == 199 then
+            has_priority_199 = true
             break
           end
         end
       end
-      assert.is_true(has_priority_200)
+      assert.is_true(has_priority_199)
       delete_buffer(bufnr)
     end)
 
@@ -984,7 +1611,7 @@ describe('highlight', function()
       end
       assert.is_true(#diff_extmark_priorities > 0)
       for _, priority in ipairs(diff_extmark_priorities) do
-        assert.is_true(priority < 200)
+        assert.is_true(priority < 199)
       end
       delete_buffer(bufnr)
     end)

spec/parser_spec.lua

@@ -359,5 +359,146 @@ describe('parser', function()
       delete_buffer(file_buf)
       delete_buffer(diff_buf)
     end)
+
+    it('detects filetype from file content shebang without open buffer', function()
+      local repo_root = '/tmp/diffs-test-shebang'
+      vim.fn.mkdir(repo_root, 'p')
+
+      local file_path = repo_root .. '/build'
+      local f = io.open(file_path, 'w')
+      f:write('#!/bin/bash\n')
+      f:write('set -e\n')
+      f:write('echo "hello"\n')
+      f:close()
+
+      local diff_buf = create_buffer({
+        'M build',
+        '@@ -1,2 +1,3 @@',
+        ' #!/bin/bash',
+        '+set -e',
+        ' echo "hello"',
+      })
+      vim.api.nvim_buf_set_var(diff_buf, 'diffs_repo_root', repo_root)
+
+      local hunks = parser.parse_buffer(diff_buf)
+
+      assert.are.equal(1, #hunks)
+      assert.are.equal('build', hunks[1].filename)
+      assert.are.equal('sh', hunks[1].ft)
+
+      delete_buffer(diff_buf)
+      os.remove(file_path)
+      vim.fn.delete(repo_root, 'rf')
+    end)
+
+    it('detects python from shebang without open buffer', function()
+      local repo_root = '/tmp/diffs-test-shebang-py'
+      vim.fn.mkdir(repo_root, 'p')
+
+      local file_path = repo_root .. '/deploy'
+      local f = io.open(file_path, 'w')
+      f:write('#!/usr/bin/env python3\n')
+      f:write('import sys\n')
+      f:write('print("hi")\n')
+      f:close()
+
+      local diff_buf = create_buffer({
+        'M deploy',
+        '@@ -1,2 +1,3 @@',
+        ' #!/usr/bin/env python3',
+        '+import sys',
+        ' print("hi")',
+      })
+      vim.api.nvim_buf_set_var(diff_buf, 'diffs_repo_root', repo_root)
+
+      local hunks = parser.parse_buffer(diff_buf)
+
+      assert.are.equal(1, #hunks)
+      assert.are.equal('deploy', hunks[1].filename)
+      assert.are.equal('python', hunks[1].ft)
+
+      delete_buffer(diff_buf)
+      os.remove(file_path)
+      vim.fn.delete(repo_root, 'rf')
+    end)
+
+    it('extracts file line numbers from @@ header', function()
+      local bufnr = create_buffer({
+        'M lua/test.lua',
+        '@@ -1,3 +1,4 @@',
+        ' local M = {}',
+        '+local new = true',
+        ' return M',
+      })
+      local hunks = parser.parse_buffer(bufnr)
+
+      assert.are.equal(1, #hunks)
+      assert.are.equal(1, hunks[1].file_old_start)
+      assert.are.equal(3, hunks[1].file_old_count)
+      assert.are.equal(1, hunks[1].file_new_start)
+      assert.are.equal(4, hunks[1].file_new_count)
+      delete_buffer(bufnr)
+    end)
+
+    it('extracts large line numbers from @@ header', function()
+      local bufnr = create_buffer({
+        'M lua/test.lua',
+        '@@ -100,20 +200,30 @@',
+        ' local M = {}',
+      })
+      local hunks = parser.parse_buffer(bufnr)
+
+      assert.are.equal(1, #hunks)
+      assert.are.equal(100, hunks[1].file_old_start)
+      assert.are.equal(20, hunks[1].file_old_count)
+      assert.are.equal(200, hunks[1].file_new_start)
+      assert.are.equal(30, hunks[1].file_new_count)
+      delete_buffer(bufnr)
+    end)
+
+    it('defaults count to 1 when omitted in @@ header', function()
+      local bufnr = create_buffer({
+        'M lua/test.lua',
+        '@@ -1 +1 @@',
+        ' local M = {}',
+      })
+      local hunks = parser.parse_buffer(bufnr)
+
+      assert.are.equal(1, #hunks)
+      assert.are.equal(1, hunks[1].file_old_start)
+      assert.are.equal(1, hunks[1].file_old_count)
+      assert.are.equal(1, hunks[1].file_new_start)
+      assert.are.equal(1, hunks[1].file_new_count)
+      delete_buffer(bufnr)
+    end)
+
+    it('stores repo_root on hunk when available', function()
+      local bufnr = create_buffer({
+        'M lua/test.lua',
+        '@@ -1,3 +1,4 @@',
+        ' local M = {}',
+        '+local new = true',
+        ' return M',
+      })
+      vim.api.nvim_buf_set_var(bufnr, 'diffs_repo_root', '/tmp/test-repo')
+      local hunks = parser.parse_buffer(bufnr)
+
+      assert.are.equal(1, #hunks)
+      assert.are.equal('/tmp/test-repo', hunks[1].repo_root)
+      delete_buffer(bufnr)
+    end)
+
+    it('repo_root is nil when not available', function()
+      local bufnr = create_buffer({
+        'M lua/test.lua',
+        '@@ -1,3 +1,4 @@',
+        ' local M = {}',
+      })
+      local hunks = parser.parse_buffer(bufnr)
+
+      assert.are.equal(1, #hunks)
+      assert.is_nil(hunks[1].repo_root)
+      delete_buffer(bufnr)
+    end)
   end)
 end)

spec/read_buffer_spec.lua

@@ -0,0 +1,400 @@
+require('spec.helpers')
+
+local commands = require('diffs.commands')
+local diffs = require('diffs')
+local git = require('diffs.git')
+
+local saved_git = {}
+local saved_systemlist
+local test_buffers = {}
+
+local function mock_git(overrides)
+  overrides = overrides or {}
+  saved_git.get_file_content = git.get_file_content
+  saved_git.get_index_content = git.get_index_content
+  saved_git.get_working_content = git.get_working_content
+
+  git.get_file_content = overrides.get_file_content
+    or function()
+      return { 'local M = {}', 'return M' }
+    end
+  git.get_index_content = overrides.get_index_content
+    or function()
+      return { 'local M = {}', 'return M' }
+    end
+  git.get_working_content = overrides.get_working_content
+    or function()
+      return { 'local M = {}', 'local x = 1', 'return M' }
+    end
+end
+
+local function mock_systemlist(fn)
+  saved_systemlist = vim.fn.systemlist
+  vim.fn.systemlist = function(cmd)
+    local result = fn(cmd)
+    saved_systemlist({ 'true' })
+    return result
+  end
+end
+
+local function restore_mocks()
+  for k, v in pairs(saved_git) do
+    git[k] = v
+  end
+  saved_git = {}
+  if saved_systemlist then
+    vim.fn.systemlist = saved_systemlist
+    saved_systemlist = nil
+  end
+end
+
+---@param name string
+---@param vars? table<string, any>
+---@return integer
+local function create_diffs_buffer(name, vars)
+  local existing = vim.fn.bufnr(name)
+  if existing ~= -1 then
+    vim.api.nvim_buf_delete(existing, { force = true })
+  end
+  local bufnr = vim.api.nvim_create_buf(false, true)
+  vim.api.nvim_buf_set_name(bufnr, name)
+  vars = vars or {}
+  for k, v in pairs(vars) do
+    vim.api.nvim_buf_set_var(bufnr, k, v)
+  end
+  table.insert(test_buffers, bufnr)
+  return bufnr
+end
+
+local function cleanup_buffers()
+  for _, bufnr in ipairs(test_buffers) do
+    if vim.api.nvim_buf_is_valid(bufnr) then
+      vim.api.nvim_buf_delete(bufnr, { force = true })
+    end
+  end
+  test_buffers = {}
+end
+
+describe('read_buffer', function()
+  after_each(function()
+    restore_mocks()
+    cleanup_buffers()
+  end)
+
+  describe('early returns', function()
+    it('does nothing on non-diffs:// buffer', function()
+      local bufnr = vim.api.nvim_create_buf(false, true)
+      table.insert(test_buffers, bufnr)
+      assert.has_no.errors(function()
+        commands.read_buffer(bufnr)
+      end)
+      assert.are.same({ '' }, vim.api.nvim_buf_get_lines(bufnr, 0, -1, false))
+    end)
+
+    it('does nothing on malformed url without colon separator', function()
+      local bufnr = create_diffs_buffer('diffs://nocolonseparator')
+      vim.api.nvim_buf_set_var(bufnr, 'diffs_repo_root', '/tmp')
+      local lines_before = vim.api.nvim_buf_get_lines(bufnr, 0, -1, false)
+      assert.has_no.errors(function()
+        commands.read_buffer(bufnr)
+      end)
+      assert.are.same(lines_before, vim.api.nvim_buf_get_lines(bufnr, 0, -1, false))
+    end)
+
+    it('does nothing when diffs_repo_root is missing', function()
+      local bufnr = create_diffs_buffer('diffs://staged:missing_root.lua')
+      assert.has_no.errors(function()
+        commands.read_buffer(bufnr)
+      end)
+      assert.are.same({ '' }, vim.api.nvim_buf_get_lines(bufnr, 0, -1, false))
+    end)
+  end)
+
+  describe('buffer options', function()
+    it('sets buftype, bufhidden, swapfile, modifiable, filetype', function()
+      mock_git()
+      local bufnr = create_diffs_buffer('diffs://staged:options_test.lua', {
+        diffs_repo_root = '/tmp',
+      })
+
+      commands.read_buffer(bufnr)
+
+      assert.are.equal('nowrite', vim.api.nvim_get_option_value('buftype', { buf = bufnr }))
+      assert.are.equal('delete', vim.api.nvim_get_option_value('bufhidden', { buf = bufnr }))
+      assert.is_false(vim.api.nvim_get_option_value('swapfile', { buf = bufnr }))
+      assert.is_false(vim.api.nvim_get_option_value('modifiable', { buf = bufnr }))
+      assert.are.equal('diff', vim.api.nvim_get_option_value('filetype', { buf = bufnr }))
+    end)
+  end)
+
+  describe('dispatch', function()
+    it('calls get_file_content + get_index_content for staged label', function()
+      local called_get_file = false
+      local called_get_index = false
+      mock_git({
+        get_file_content = function()
+          called_get_file = true
+          return { 'old' }
+        end,
+        get_index_content = function()
+          called_get_index = true
+          return { 'new' }
+        end,
+      })
+
+      local bufnr = create_diffs_buffer('diffs://staged:dispatch_staged.lua', {
+        diffs_repo_root = '/tmp',
+      })
+      commands.read_buffer(bufnr)
+
+      assert.is_true(called_get_file)
+      assert.is_true(called_get_index)
+    end)
+
+    it('calls get_index_content + get_working_content for unstaged label', function()
+      local called_get_index = false
+      local called_get_working = false
+      mock_git({
+        get_index_content = function()
+          called_get_index = true
+          return { 'index' }
+        end,
+        get_working_content = function()
+          called_get_working = true
+          return { 'working' }
+        end,
+      })
+
+      local bufnr = create_diffs_buffer('diffs://unstaged:dispatch_unstaged.lua', {
+        diffs_repo_root = '/tmp',
+      })
+      commands.read_buffer(bufnr)
+
+      assert.is_true(called_get_index)
+      assert.is_true(called_get_working)
+    end)
+
+    it('calls only get_working_content for untracked label', function()
+      local called_get_file = false
+      local called_get_working = false
+      mock_git({
+        get_file_content = function()
+          called_get_file = true
+          return {}
+        end,
+        get_working_content = function()
+          called_get_working = true
+          return { 'new file' }
+        end,
+      })
+
+      local bufnr = create_diffs_buffer('diffs://untracked:dispatch_untracked.lua', {
+        diffs_repo_root = '/tmp',
+      })
+      commands.read_buffer(bufnr)
+
+      assert.is_false(called_get_file)
+      assert.is_true(called_get_working)
+    end)
+
+    it('calls get_file_content + get_working_content for revision label', function()
+      local captured_rev
+      local called_get_working = false
+      mock_git({
+        get_file_content = function(rev)
+          captured_rev = rev
+          return { 'old' }
+        end,
+        get_working_content = function()
+          called_get_working = true
+          return { 'new' }
+        end,
+      })
+
+      local bufnr = create_diffs_buffer('diffs://HEAD~3:dispatch_rev.lua', {
+        diffs_repo_root = '/tmp',
+      })
+      commands.read_buffer(bufnr)
+
+      assert.are.equal('HEAD~3', captured_rev)
+      assert.is_true(called_get_working)
+    end)
+
+    it('falls back from index to HEAD for unstaged when index returns nil', function()
+      local call_order = {}
+      mock_git({
+        get_index_content = function()
+          table.insert(call_order, 'index')
+          return nil
+        end,
+        get_file_content = function()
+          table.insert(call_order, 'head')
+          return { 'head content' }
+        end,
+        get_working_content = function()
+          return { 'working content' }
+        end,
+      })
+
+      local bufnr = create_diffs_buffer('diffs://unstaged:dispatch_fallback.lua', {
+        diffs_repo_root = '/tmp',
+      })
+      commands.read_buffer(bufnr)
+
+      assert.are.same({ 'index', 'head' }, call_order)
+    end)
+
+    it('runs git diff for section diffs with path=all', function()
+      local captured_cmd
+      mock_systemlist(function(cmd)
+        captured_cmd = cmd
+        return {
+          'diff --git a/file.lua b/file.lua',
+          '--- a/file.lua',
+          '+++ b/file.lua',
+          '@@ -1 +1 @@',
+          '-old',
+          '+new',
+        }
+      end)
+
+      local bufnr = create_diffs_buffer('diffs://unstaged:all', {
+        diffs_repo_root = '/home/test/repo',
+      })
+      commands.read_buffer(bufnr)
+
+      assert.is_not_nil(captured_cmd)
+      assert.are.equal('git', captured_cmd[1])
+      assert.are.equal('/home/test/repo', captured_cmd[3])
+      assert.are.equal('diff', captured_cmd[4])
+
+      local lines = vim.api.nvim_buf_get_lines(bufnr, 0, -1, false)
+      assert.are.equal('diff --git a/file.lua b/file.lua', lines[1])
+    end)
+
+    it('passes --cached for staged section diffs', function()
+      local captured_cmd
+      mock_systemlist(function(cmd)
+        captured_cmd = cmd
+        return { 'diff --git a/f.lua b/f.lua', '@@ -1 +1 @@', '-a', '+b' }
+      end)
+
+      local bufnr = create_diffs_buffer('diffs://staged:all', {
+        diffs_repo_root = '/tmp',
+      })
+      commands.read_buffer(bufnr)
+
+      assert.is_truthy(vim.tbl_contains(captured_cmd, '--cached'))
+    end)
+  end)
+
+  describe('content', function()
+    it('generates valid unified diff header with correct paths', function()
+      mock_git({
+        get_file_content = function()
+          return { 'old' }
+        end,
+        get_working_content = function()
+          return { 'new' }
+        end,
+      })
+
+      local bufnr = create_diffs_buffer('diffs://HEAD:lua/diffs/init.lua', {
+        diffs_repo_root = '/tmp',
+      })
+      commands.read_buffer(bufnr)
+
+      local lines = vim.api.nvim_buf_get_lines(bufnr, 0, -1, false)
+      assert.are.equal('diff --git a/lua/diffs/init.lua b/lua/diffs/init.lua', lines[1])
+      assert.are.equal('--- a/lua/diffs/init.lua', lines[2])
+      assert.are.equal('+++ b/lua/diffs/init.lua', lines[3])
+    end)
+
+    it('uses old_filepath for diff header in renames', function()
+      mock_git({
+        get_file_content = function(_, path)
+          assert.are.equal('/tmp/old_name.lua', path)
+          return { 'old content' }
+        end,
+        get_index_content = function()
+          return { 'new content' }
+        end,
+      })
+
+      local bufnr = create_diffs_buffer('diffs://staged:new_name.lua', {
+        diffs_repo_root = '/tmp',
+        diffs_old_filepath = 'old_name.lua',
+      })
+      commands.read_buffer(bufnr)
+
+      local lines = vim.api.nvim_buf_get_lines(bufnr, 0, -1, false)
+      assert.are.equal('diff --git a/old_name.lua b/new_name.lua', lines[1])
+      assert.are.equal('--- a/old_name.lua', lines[2])
+      assert.are.equal('+++ b/new_name.lua', lines[3])
+    end)
+
+    it('produces empty buffer when old and new are identical', function()
+      mock_git({
+        get_file_content = function()
+          return { 'identical' }
+        end,
+        get_working_content = function()
+          return { 'identical' }
+        end,
+      })
+
+      local bufnr = create_diffs_buffer('diffs://HEAD:nodiff.lua', {
+        diffs_repo_root = '/tmp',
+      })
+      commands.read_buffer(bufnr)
+
+      local lines = vim.api.nvim_buf_get_lines(bufnr, 0, -1, false)
+      assert.are.same({ '' }, lines)
+    end)
+
+    it('replaces existing buffer content on reload', function()
+      mock_git({
+        get_file_content = function()
+          return { 'old' }
+        end,
+        get_working_content = function()
+          return { 'new' }
+        end,
+      })
+
+      local bufnr = create_diffs_buffer('diffs://HEAD:replace_test.lua', {
+        diffs_repo_root = '/tmp',
+      })
+      vim.api.nvim_buf_set_lines(bufnr, 0, -1, false, { 'stale', 'content', 'from', 'before' })
+
+      commands.read_buffer(bufnr)
+
+      local lines = vim.api.nvim_buf_get_lines(bufnr, 0, -1, false)
+      assert.are.equal('diff --git a/replace_test.lua b/replace_test.lua', lines[1])
+      for _, line in ipairs(lines) do
+        assert.is_not_equal('stale', line)
+      end
+    end)
+  end)
+
+  describe('attach integration', function()
+    it('calls attach on the buffer', function()
+      mock_git()
+
+      local attach_called_with
+      local original_attach = diffs.attach
+      diffs.attach = function(bufnr)
+        attach_called_with = bufnr
+      end
+
+      local bufnr = create_diffs_buffer('diffs://staged:attach_test.lua', {
+        diffs_repo_root = '/tmp',
+      })
+      commands.read_buffer(bufnr)
+
+      assert.are.equal(bufnr, attach_called_with)
+
+      diffs.attach = original_attach
+    end)
+  end)
+end)

spec/ux_spec.lua

@@ -0,0 +1,135 @@
+local commands = require('diffs.commands')
+local helpers = require('spec.helpers')
+
+local counter = 0
+
+local function create_diffs_buffer(name)
+  counter = counter + 1
+  local bufnr = vim.api.nvim_create_buf(false, true)
+  vim.api.nvim_buf_set_lines(bufnr, 0, -1, false, {
+    'diff --git a/file.lua b/file.lua',
+    '--- a/file.lua',
+    '+++ b/file.lua',
+    '@@ -1,1 +1,2 @@',
+    ' local x = 1',
+    '+local y = 2',
+  })
+  vim.api.nvim_set_option_value('buftype', 'nowrite', { buf = bufnr })
+  vim.api.nvim_set_option_value('bufhidden', 'wipe', { buf = bufnr })
+  vim.api.nvim_set_option_value('swapfile', false, { buf = bufnr })
+  vim.api.nvim_set_option_value('modifiable', false, { buf = bufnr })
+  vim.api.nvim_set_option_value('filetype', 'diff', { buf = bufnr })
+  vim.api.nvim_buf_set_name(bufnr, name or ('diffs://unstaged:file_' .. counter .. '.lua'))
+  return bufnr
+end
+
+describe('ux', function()
+  describe('diagnostics', function()
+    it('disables diagnostics on diff buffers', function()
+      local bufnr = create_diffs_buffer()
+      commands.setup_diff_buf(bufnr)
+
+      assert.is_false(vim.diagnostic.is_enabled({ bufnr = bufnr }))
+      vim.api.nvim_buf_delete(bufnr, { force = true })
+    end)
+
+    it('does not affect other buffers', function()
+      local diff_buf = create_diffs_buffer()
+      local normal_buf = helpers.create_buffer({ 'hello' })
+
+      commands.setup_diff_buf(diff_buf)
+
+      assert.is_true(vim.diagnostic.is_enabled({ bufnr = normal_buf }))
+      vim.api.nvim_buf_delete(diff_buf, { force = true })
+      helpers.delete_buffer(normal_buf)
+    end)
+  end)
+
+  describe('q keymap', function()
+    it('sets q keymap on diff buffer', function()
+      local bufnr = create_diffs_buffer()
+      commands.setup_diff_buf(bufnr)
+
+      local keymaps = vim.api.nvim_buf_get_keymap(bufnr, 'n')
+      local has_q = false
+      for _, km in ipairs(keymaps) do
+        if km.lhs == 'q' then
+          has_q = true
+          break
+        end
+      end
+      assert.is_true(has_q)
+      vim.api.nvim_buf_delete(bufnr, { force = true })
+    end)
+
+    it('q closes the window', function()
+      local bufnr = create_diffs_buffer()
+      commands.setup_diff_buf(bufnr)
+
+      vim.cmd('split')
+      local win = vim.api.nvim_get_current_win()
+      vim.api.nvim_win_set_buf(win, bufnr)
+
+      local win_count_before = #vim.api.nvim_tabpage_list_wins(0)
+
+      vim.api.nvim_buf_call(bufnr, function()
+        vim.cmd('normal q')
+      end)
+
+      local win_count_after = #vim.api.nvim_tabpage_list_wins(0)
+      assert.equals(win_count_before - 1, win_count_after)
+    end)
+  end)
+
+  describe('window reuse', function()
+    it('returns nil when no diffs window exists', function()
+      local win = commands.find_diffs_window()
+      assert.is_nil(win)
+    end)
+
+    it('finds existing diffs:// window', function()
+      local bufnr = create_diffs_buffer()
+      vim.cmd('split')
+      local expected_win = vim.api.nvim_get_current_win()
+      vim.api.nvim_win_set_buf(expected_win, bufnr)
+
+      local found = commands.find_diffs_window()
+      assert.equals(expected_win, found)
+
+      vim.api.nvim_win_close(expected_win, true)
+    end)
+
+    it('ignores non-diffs buffers', function()
+      local normal_buf = helpers.create_buffer({ 'hello' })
+      vim.cmd('split')
+      local win = vim.api.nvim_get_current_win()
+      vim.api.nvim_win_set_buf(win, normal_buf)
+
+      local found = commands.find_diffs_window()
+      assert.is_nil(found)
+
+      vim.api.nvim_win_close(win, true)
+      helpers.delete_buffer(normal_buf)
+    end)
+
+    it('returns first diffs window when multiple exist', function()
+      local buf1 = create_diffs_buffer()
+      local buf2 = create_diffs_buffer()
+
+      vim.cmd('split')
+      local win1 = vim.api.nvim_get_current_win()
+      vim.api.nvim_win_set_buf(win1, buf1)
+
+      vim.cmd('split')
+      local win2 = vim.api.nvim_get_current_win()
+      vim.api.nvim_win_set_buf(win2, buf2)
+
+      local found = commands.find_diffs_window()
+      assert.is_not_nil(found)
+      assert.is_true(found == win1 or found == win2)
+
+      vim.api.nvim_win_close(win1, true)
+      vim.api.nvim_win_close(win2, true)
+    end)
+  end)
+end)