refactor(highlight): unified per-line extmark builder (#144)

## Problem

`highlight_hunk` applied DiffsClear extmarks across 5 scattered sites
with
ad-hoc column arithmetic. This fragmentation produced the 1-column
DiffsClear
gap on email-quoted body context lines (#142 issue 1). A redundant
`highlight_hunk_vim_syntax` function duplicated the inline vim syntax
path,
and the deferred pass in init.lua double-called it, creating duplicate
scratch
buffers and extmarks.

## Solution

Reorganize `highlight_hunk` into two clean phases:

- **Phase 1** — multi-line syntax computation (treesitter, vim syntax,
diff
grammar, header context text). Sets syntax extmarks only, no DiffsClear.
- **Phase 2** — per-line chrome (DiffsClear, backgrounds, gutter,
overlays,
  intra-line). All non-syntax extmarks consolidated in one pass.

Hoist `new_code` to function scope (needed by `highlight_text` outside
the
`use_ts` block). Hoist `at_raw_line` so Phase 1d and Phase 2b share one
`nvim_buf_get_lines` call.

Delete `highlight_hunk_vim_syntax` (redundant with inline path). Remove
the
double-call from the deferred pass in init.lua.

Extend body prefix DiffsClear `end_col` from `qw` to `pw + qw`, fixing
the
1-column gap where native treesitter background bled through on context
lines
in email-quoted diffs (#142 issue 1).

### Email-quoted diff support

The parser now strips `> ` (and `>> `, etc.) email quote prefixes before
pattern matching, enabling syntax highlighting for diffs embedded in
email
replies and `git-send-email` / sourcehut-style patch review threads.
Each hunk stores `quote_width` so the highlight pipeline can apply
`DiffsClear` at the correct column offsets to suppress native treesitter
on quoted regions.

Closes #141

### #142 status after this PR

| Sub-issue | Status |
|-----------|--------|
| 1. Col gap on context lines | Fixed |
| 2. Bare `>` context lines | Improved, edge case remains |
| 3. Diff prefix marker fg | Not addressed (follow-up) |

.luarc.json

@@ -2,7 +2,14 @@
   "runtime.version": "LuaJIT",
   "runtime.path": ["lua/?.lua", "lua/?/init.lua"],
   "diagnostics.globals": ["vim", "jit"],
-  "workspace.library": ["$VIMRUNTIME/lua", "${3rd}/luv/library"],
+  "workspace.library": [
+    "$VIMRUNTIME/lua",
+    "${3rd}/luv/library",
+    "${3rd}/busted/library",
+    "${3rd}/luassert/library"
+  ],
   "workspace.checkThirdParty": false,
+  "diagnostics.libraryFiles": "Disable",
+  "workspace.ignoreDir": [".direnv"],
   "completion.callSnippet": "Replace"
 }

.styluaignore

@@ -0,0 +1 @@
+.direnv/

README.md

@@ -17,6 +17,8 @@ with language-aware syntax highlighting.
 - `:Gdiff` unified diff against any revision
 - Background-only diff colors for `&diff` buffers
 - Inline merge conflict detection, highlighting, and resolution
+- Email-quoted diff highlighting (`> diff ...` prefixes, arbitrary nesting
+  depth)
 - Vim syntax fallback, configurable blend/priorities
 
 ## Requirements

flake.nix

@@ -13,24 +13,41 @@
       ...
     }:
     let
-      forEachSystem = f: nixpkgs.lib.genAttrs (import systems) (system: f nixpkgs.legacyPackages.${system});
+      forEachSystem =
+        f: nixpkgs.lib.genAttrs (import systems) (system: f nixpkgs.legacyPackages.${system});
     in
     {
+      formatter = forEachSystem (pkgs: pkgs.nixfmt-tree);
+
       devShells = forEachSystem (pkgs: {
-        default = pkgs.mkShell {
+        default =
-          packages = [
+          let
-            (pkgs.luajit.withPackages (
+            ts-plugin = pkgs.vimPlugins.nvim-treesitter.withPlugins (p: [ p.diff ]);
+            diff-grammar = pkgs.vimPlugins.nvim-treesitter-parsers.diff;
+            luaEnv = pkgs.luajit.withPackages (
               ps: with ps; [
                 busted
                 nlua
               ]
-            ))
+            );
-            pkgs.prettier
+            busted-with-grammar = pkgs.writeShellScriptBin "busted" ''
-            pkgs.stylua
+              nvim_bin=$(which nvim)
-            pkgs.selene
+              tmpdir=$(mktemp -d)
-            pkgs.lua-language-server
+              trap 'rm -rf "$tmpdir"' EXIT
-          ];
+              printf '#!/bin/sh\nexec "%s" --cmd "set rtp+=${ts-plugin}/runtime" --cmd "set rtp+=${diff-grammar}" "$@"\n' "$nvim_bin" > "$tmpdir/nvim"
-        };
+              chmod +x "$tmpdir/nvim"
+              PATH="$tmpdir:$PATH" exec ${luaEnv}/bin/busted "$@"
+            '';
+          in
+          pkgs.mkShell {
+            packages = [
+              busted-with-grammar
+              pkgs.prettier
+              pkgs.stylua
+              pkgs.selene
+              pkgs.lua-language-server
+            ];
+          };
       });
     };
 }

lua/diffs/highlight.lua

@@ -74,6 +74,7 @@ end
 ---@param col_offset integer
 ---@param covered_lines? table<integer, true>
 ---@param priorities diffs.PrioritiesConfig
+---@param force_high_priority? boolean
 ---@return integer
 local function highlight_treesitter(
   bufnr,
@@ -83,7 +84,8 @@ local function highlight_treesitter(
   line_map,
   col_offset,
   covered_lines,
-  priorities
+  priorities,
+  force_high_priority
 )
   local code = table.concat(code_lines, '\n')
   if code == '' then
@@ -123,7 +125,9 @@ local function highlight_treesitter(
           local buf_sc = sc + col_offset
           local buf_ec = ec + col_offset
 
-          local priority = tree_lang == 'diff' and (tonumber(metadata.priority) or 100)
+          local meta_prio = tonumber(metadata.priority) or 100
+          local priority = tree_lang == 'diff'
+              and ((col_offset > 0 or force_high_priority) and (priorities.syntax + meta_prio - 100) or meta_prio)
             or priorities.syntax
 
           pcall(vim.api.nvim_buf_set_extmark, bufnr, ns, buf_sr, buf_sc, {
@@ -221,7 +225,7 @@ local function highlight_vim_syntax(
 
   pcall(vim.api.nvim_buf_call, scratch, function()
     vim.cmd('setlocal syntax=' .. ft)
-    vim.cmd('redraw')
+    vim.cmd.redraw()
 
     ---@param line integer
     ---@param col integer
@@ -292,9 +296,10 @@ function M.highlight_hunk(bufnr, ns, hunk, opts)
   local covered_lines = {}
 
   local extmark_count = 0
+  ---@type string[]
+  local new_code = {}
+
   if use_ts then
-    ---@type string[]
-    local new_code = {}
     ---@type table<integer, integer>
     local new_map = {}
     ---@type string[]
@@ -328,12 +333,6 @@ function M.highlight_hunk(bufnr, ns, hunk, opts)
       + highlight_treesitter(bufnr, ns, old_code, hunk.lang, old_map, pw, covered_lines, p)
 
     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 = p.clear,
-      })
       local header_extmarks = highlight_text(
         bufnr,
         ns,
@@ -370,7 +369,13 @@ function M.highlight_hunk(bufnr, ns, hunk, opts)
       header_map[i] = hunk.header_start_line - 1 + i
     end
     extmark_count = extmark_count
-      + highlight_treesitter(bufnr, ns, hunk.header_lines, 'diff', header_map, 0, nil, p)
+      + highlight_treesitter(bufnr, ns, hunk.header_lines, 'diff', header_map, 0, nil, p, pw > 1)
+  end
+
+  local at_raw_line
+  if pw > 1 and opts.highlights.treesitter.enabled then
+    local at_buf_line = hunk.start_line - 1
+    at_raw_line = vim.api.nvim_buf_get_lines(bufnr, at_buf_line, at_buf_line + 1, false)[1]
   end
 
   ---@type diffs.IntraChanges?
@@ -407,6 +412,69 @@ function M.highlight_hunk(bufnr, ns, hunk, opts)
     end
   end
 
+  if
+    pw > 1
+    and hunk.header_start_line
+    and hunk.header_lines
+    and #hunk.header_lines > 0
+    and opts.highlights.treesitter.enabled
+  then
+    for i = 0, #hunk.header_lines - 1 do
+      local buf_line = hunk.header_start_line - 1 + i
+      pcall(vim.api.nvim_buf_set_extmark, bufnr, ns, buf_line, 0, {
+        end_col = #hunk.header_lines[i + 1],
+        hl_group = 'DiffsClear',
+        priority = p.clear,
+      })
+
+      local hline = hunk.header_lines[i + 1]
+      if hline:match('^index ') then
+        pcall(vim.api.nvim_buf_set_extmark, bufnr, ns, buf_line, 0, {
+          end_col = 5,
+          hl_group = '@keyword.diff',
+          priority = p.syntax,
+        })
+        local dot_pos = hline:find('%.%.', 1, false)
+        if dot_pos then
+          local rest = hline:sub(dot_pos + 2)
+          local hash = rest:match('^(%x+)')
+          if hash then
+            pcall(vim.api.nvim_buf_set_extmark, bufnr, ns, buf_line, dot_pos + 1, {
+              end_col = dot_pos + 1 + #hash,
+              hl_group = '@constant.diff',
+              priority = p.syntax,
+            })
+          end
+        end
+      end
+    end
+  end
+
+  if pw > 1 and at_raw_line then
+    local at_buf_line = hunk.start_line - 1
+    pcall(vim.api.nvim_buf_set_extmark, bufnr, ns, at_buf_line, 0, {
+      end_col = #at_raw_line,
+      hl_group = 'DiffsClear',
+      priority = p.clear,
+    })
+    if opts.highlights.treesitter.enabled then
+      pcall(vim.api.nvim_buf_set_extmark, bufnr, ns, at_buf_line, 0, {
+        end_col = #at_raw_line,
+        hl_group = '@attribute.diff',
+        priority = p.syntax,
+      })
+    end
+  end
+
+  if use_ts and 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 = p.clear,
+    })
+  end
+
   for i, line in ipairs(hunk.lines) do
     local buf_line = hunk.start_line + i - 1
     local line_len = #line
@@ -434,6 +502,24 @@ function M.highlight_hunk(bufnr, ns, hunk, opts)
       })
     end
 
+    if pw > 1 then
+      pcall(vim.api.nvim_buf_set_extmark, bufnr, ns, buf_line, 0, {
+        end_col = pw,
+        hl_group = 'DiffsClear',
+        priority = p.clear,
+      })
+      for ci = 0, pw - 1 do
+        local ch = line:sub(ci + 1, ci + 1)
+        if ch == '+' or ch == '-' then
+          pcall(vim.api.nvim_buf_set_extmark, bufnr, ns, buf_line, ci, {
+            end_col = ci + 1,
+            hl_group = ch == '+' and '@diff.plus' or '@diff.minus',
+            priority = p.syntax,
+          })
+        end
+      end
+    end
+
     if line_len > pw and covered_lines[buf_line] then
       pcall(vim.api.nvim_buf_set_extmark, bufnr, ns, buf_line, pw, {
         end_col = line_len,
@@ -444,17 +530,10 @@ function M.highlight_hunk(bufnr, ns, hunk, opts)
 
     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,
+        line_hl_group = line_hl,
-        hl_group = line_hl,
+        number_hl_group = opts.highlights.gutter and number_hl or nil,
-        hl_eol = true,
         priority = p.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 = p.line_bg,
-        })
-      end
     end
 
     if is_marker and line_len > pw then
@@ -493,40 +572,4 @@ function M.highlight_hunk(bufnr, ns, hunk, opts)
   dbg('hunk %s:%d applied %d extmarks', hunk.filename, hunk.start_line, extmark_count)
 end
 
----@param bufnr integer
----@param ns integer
----@param hunk diffs.Hunk
----@param opts diffs.HunkOpts
-function M.highlight_hunk_vim_syntax(bufnr, ns, hunk, opts)
-  local p = opts.highlights.priorities
-  local pw = hunk.prefix_width or 1
-
-  if not hunk.ft or #hunk.lines == 0 then
-    return
-  end
-
-  if #hunk.lines > opts.highlights.vim.max_lines then
-    return
-  end
-
-  local code_lines = {}
-  for _, line in ipairs(hunk.lines) do
-    table.insert(code_lines, line:sub(pw + 1))
-  end
-
-  local covered_lines = {}
-  highlight_vim_syntax(bufnr, ns, hunk, code_lines, covered_lines, 0, p)
-
-  for buf_line in pairs(covered_lines) do
-    local line = hunk.lines[buf_line - hunk.start_line + 1]
-    if line and #line > pw then
-      pcall(vim.api.nvim_buf_set_extmark, bufnr, ns, buf_line, pw, {
-        end_col = #line,
-        hl_group = 'DiffsClear',
-        priority = p.clear,
-      })
-    end
-  end
-end
-
 return M

lua/diffs/init.lua

@@ -169,6 +169,9 @@ local fast_hl_opts = {} ---@type diffs.HunkOpts
 ---@type table<integer, boolean>
 local attached_buffers = {}
 
+---@type table<integer, boolean>
+local ft_retry_pending = {}
+
 ---@type table<integer, boolean>
 local diff_windows = {}
 
@@ -334,12 +337,15 @@ local function ensure_cache(bufnr)
       has_nil_ft = true
     end
   end
-  if has_nil_ft and vim.fn.did_filetype() ~= 0 then
+  if has_nil_ft and vim.fn.did_filetype() ~= 0 and not ft_retry_pending[bufnr] then
+    ft_retry_pending[bufnr] = true
     vim.schedule(function()
       if vim.api.nvim_buf_is_valid(bufnr) and hunk_cache[bufnr] then
         dbg('retrying filetype detection for buffer %d (was blocked by did_filetype)', bufnr)
         invalidate_cache(bufnr)
+        vim.cmd('redraw!')
       end
+      ft_retry_pending[bufnr] = nil
     end)
   end
 end
@@ -411,7 +417,7 @@ local function compute_highlight_groups()
   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, 'DiffsClear', { default = true, fg = normal.fg or 0xc0c0c0, bg = bg })
   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 = blended_add_text, bg = blended_add })
@@ -759,7 +765,7 @@ local function init()
         if not entry.highlighted[i] then
           local hunk = entry.hunks[i]
           local clear_start = hunk.start_line - 1
-          local clear_end = clear_start + #hunk.lines
+          local clear_end = hunk.start_line + #hunk.lines
           if hunk.header_start_line then
             clear_start = hunk.header_start_line - 1
           end
@@ -776,12 +782,18 @@ local function init()
       end
       if #deferred_syntax > 0 then
         local tick = entry.tick
+        dbg('deferred syntax scheduled: %d hunks tick=%d', #deferred_syntax, tick)
         vim.schedule(function()
           if not vim.api.nvim_buf_is_valid(bufnr) then
             return
           end
           local cur = hunk_cache[bufnr]
           if not cur or cur.tick ~= tick then
+            dbg(
+              'deferred syntax stale: cur.tick=%s captured=%d',
+              cur and tostring(cur.tick) or 'nil',
+              tick
+            )
             return
           end
           local t1 = config.debug and vim.uv.hrtime() or nil
@@ -791,15 +803,12 @@ local function init()
           }
           for _, hunk in ipairs(deferred_syntax) do
             local start_row = hunk.start_line - 1
-            local end_row = start_row + #hunk.lines
+            local end_row = hunk.start_line + #hunk.lines
             if hunk.header_start_line then
               start_row = hunk.header_start_line - 1
             end
             vim.api.nvim_buf_clear_namespace(bufnr, ns, start_row, end_row)
             highlight.highlight_hunk(bufnr, ns, hunk, full_opts)
-            if not hunk.lang and hunk.ft then
-              highlight.highlight_hunk_vim_syntax(bufnr, ns, hunk, full_opts)
-            end
           end
           if t1 then
             dbg('deferred pass: %d hunks in %.2fms', #deferred_syntax, (vim.uv.hrtime() - t1) / 1e6)
@@ -866,6 +875,7 @@ function M.attach(bufnr)
     callback = function()
       attached_buffers[bufnr] = nil
       hunk_cache[bufnr] = nil
+      ft_retry_pending[bufnr] = nil
       if neogit_augroup then
         pcall(vim.api.nvim_del_augroup_by_id, neogit_augroup)
       end
@@ -947,6 +957,7 @@ M._test = {
   invalidate_cache = invalidate_cache,
   hunks_eq = hunks_eq,
   process_pending_clear = process_pending_clear,
+  ft_retry_pending = ft_retry_pending,
 }
 
 return M

lua/diffs/parser.lua

@@ -60,6 +60,15 @@ local function get_ft_from_filename(filename, repo_root)
   end
 
   local ft = vim.filetype.match({ filename = filename })
+  if not ft and vim.fn.did_filetype() ~= 0 then
+    dbg('retrying filetype match for %s (clearing did_filetype)', filename)
+    local saved = rawget(vim.fn, 'did_filetype')
+    rawset(vim.fn, 'did_filetype', function()
+      return 0
+    end)
+    ft = vim.filetype.match({ filename = filename })
+    rawset(vim.fn, 'did_filetype', saved)
+  end
   if ft then
     dbg('filetype from filename: %s', ft)
     return ft
@@ -125,6 +134,7 @@ end
 function M.parse_buffer(bufnr)
   local lines = vim.api.nvim_buf_get_lines(bufnr, 0, -1, false)
   local repo_root = get_repo_root(bufnr)
+
   ---@type diffs.Hunk[]
   local hunks = {}
 
@@ -162,7 +172,6 @@ function M.parse_buffer(bufnr)
   local old_remaining = nil
   ---@type integer?
   local new_remaining = nil
-  local is_unified_diff = false
 
   local function flush_hunk()
     if hunk_start and #hunk_lines > 0 then
@@ -201,6 +210,8 @@ function M.parse_buffer(bufnr)
 
   for i, line in ipairs(lines) do
     local diff_git_file = line:match('^diff %-%-git a/.+ b/(.+)$')
+      or line:match('^diff %-%-combined (.+)$')
+      or line:match('^diff %-%-cc (.+)$')
     local neogit_file = line:match('^modified%s+(.+)$')
       or (not line:match('^new file mode') and line:match('^new file%s+(.+)$'))
       or (not line:match('^deleted file mode') and line:match('^deleted%s+(.+)$'))
@@ -209,7 +220,6 @@ function M.parse_buffer(bufnr)
     local bare_file = not hunk_start and line:match('^([^%s]+%.[^%s]+)$')
     local filename = line:match('^[MADRCU%?!]%s+(.+)$') or diff_git_file or neogit_file or bare_file
     if filename then
-      is_unified_diff = diff_git_file ~= nil
       flush_hunk()
       current_filename = filename
       local cache_key = (repo_root or '') .. '\0' .. filename
@@ -249,10 +259,17 @@ function M.parse_buffer(bufnr)
           new_remaining = file_new_count
         end
       else
+        local hs, hc = line:match('%-(%d+),?(%d*)')
+        if hs then
+          file_old_start = tonumber(hs)
+          file_old_count = tonumber(hc) or 1
+          old_remaining = file_old_count
+        end
         local hs2, hc2 = line:match('%+(%d+),?(%d*) @@')
         if hs2 then
           file_new_start = tonumber(hs2)
           file_new_count = tonumber(hc2) or 1
+          new_remaining = file_new_count
         end
       end
       local at_end, context = line:match('^(@@+.-@@+%s*)(.*)')
@@ -275,13 +292,12 @@ function M.parse_buffer(bufnr)
         end
       elseif
         line == ''
-        and is_unified_diff
         and old_remaining
         and old_remaining > 0
         and new_remaining
         and new_remaining > 0
       then
-        table.insert(hunk_lines, ' ')
+        table.insert(hunk_lines, string.rep(' ', hunk_prefix_width))
         old_remaining = old_remaining - 1
         new_remaining = new_remaining - 1
       elseif

scripts/ci.sh

@@ -0,0 +1,10 @@
+#!/bin/sh
+set -eu
+
+nix develop --command stylua --check .
+git ls-files '*.lua' | xargs nix develop --command selene --display-style quiet
+nix develop --command prettier --check .
+nix fmt
+git diff --exit-code -- '*.nix'
+nix develop --command lua-language-server --check . --checklevel=Warning
+nix develop --command busted

spec/highlight_spec.lua

@@ -287,7 +287,7 @@ 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].hl_group == 'DiffsAdd' then
+        if mark[4] and mark[4].line_hl_group == 'DiffsAdd' then
           has_diff_add = true
           break
         end
@@ -320,7 +320,7 @@ 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].hl_group == 'DiffsDelete' then
+        if mark[4] and mark[4].line_hl_group == 'DiffsDelete' then
           has_diff_delete = true
           break
         end
@@ -362,6 +362,122 @@ describe('highlight', function()
       delete_buffer(bufnr)
     end)
 
+    it('line bg uses line_hl_group not hl_group with end_row', 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' },
+      }
+
+      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]
+        assert.is_not_equal('DiffsAdd', d and d.hl_group)
+        assert.is_not_equal('DiffsDelete', d and d.hl_group)
+      end
+      delete_buffer(bufnr)
+    end)
+
+    it('line bg extmark survives adjacent clear_namespace starting at next row', function()
+      local bufnr = create_buffer({
+        'diff --git a/foo.py b/foo.py',
+        '@@ -1,2 +1,2 @@',
+        '-old',
+        '+new',
+      })
+
+      local hunk = {
+        filename = 'foo.py',
+        header_start_line = 1,
+        start_line = 2,
+        lines = { '-old', '+new' },
+        prefix_width = 1,
+      }
+
+      highlight.highlight_hunk(
+        bufnr,
+        ns,
+        hunk,
+        default_opts({ highlights = { background = true, treesitter = { enabled = false } } })
+      )
+
+      local last_body_row = hunk.start_line + #hunk.lines - 1
+      vim.api.nvim_buf_clear_namespace(bufnr, ns, last_body_row + 1, last_body_row + 10)
+
+      local marks = vim.api.nvim_buf_get_extmarks(
+        bufnr,
+        ns,
+        { last_body_row, 0 },
+        { last_body_row, -1 },
+        { details = true }
+      )
+      local has_line_bg = false
+      for _, mark in ipairs(marks) do
+        if mark[4] and mark[4].line_hl_group == 'DiffsAdd' then
+          has_line_bg = true
+        end
+      end
+      assert.is_true(has_line_bg)
+      delete_buffer(bufnr)
+    end)
+
+    it('clear range covers last body line of hunk with header', function()
+      local bufnr = create_buffer({
+        'diff --git a/foo.py b/foo.py',
+        'index abc..def 100644',
+        '--- a/foo.py',
+        '+++ b/foo.py',
+        '@@ -1,3 +1,3 @@',
+        ' ctx',
+        '-old',
+        '+new',
+      })
+
+      local hunk = {
+        filename = 'foo.py',
+        header_start_line = 1,
+        start_line = 5,
+        lines = { ' ctx', '-old', '+new' },
+        prefix_width = 1,
+      }
+
+      highlight.highlight_hunk(
+        bufnr,
+        ns,
+        hunk,
+        default_opts({ highlights = { background = true, treesitter = { enabled = false } } })
+      )
+
+      local last_body_row = hunk.start_line + #hunk.lines - 1
+      local clear_start = hunk.header_start_line - 1
+      local clear_end = hunk.start_line + #hunk.lines
+      vim.api.nvim_buf_clear_namespace(bufnr, ns, clear_start, clear_end)
+
+      local marks = vim.api.nvim_buf_get_extmarks(
+        bufnr,
+        ns,
+        { last_body_row, 0 },
+        { last_body_row, -1 },
+        { details = false }
+      )
+      assert.are.equal(0, #marks)
+      delete_buffer(bufnr)
+    end)
+
     it('still applies background when treesitter disabled', function()
       local bufnr = create_buffer({
         '@@ -1,1 +1,2 @@',
@@ -386,7 +502,7 @@ 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].hl_group == 'DiffsAdd' then
+        if mark[4] and mark[4].line_hl_group == 'DiffsAdd' then
           has_diff_add = true
           break
         end
@@ -500,7 +616,7 @@ 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].hl_group == 'DiffsAdd' then
+        if mark[4] and mark[4].line_hl_group == 'DiffsAdd' then
           has_diff_add = true
           break
         end
@@ -585,7 +701,7 @@ describe('highlight', function()
       local found = false
       for _, mark in ipairs(extmarks) do
         local d = mark[4]
-        if d and (d.hl_group == 'DiffsAdd' or d.hl_group == 'DiffsDelete') and d.hl_eol then
+        if d and (d.line_hl_group == 'DiffsAdd' or d.line_hl_group == 'DiffsDelete') then
           found = true
         end
       end
@@ -741,7 +857,7 @@ describe('highlight', function()
         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') and d.hl_eol then
+          elseif d.line_hl_group == 'DiffsAdd' or d.line_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)
@@ -842,8 +958,8 @@ describe('highlight', function()
       local line_bgs = {}
       for _, mark in ipairs(extmarks) do
         local d = mark[4]
-        if d and (d.hl_group == 'DiffsAdd' or d.hl_group == 'DiffsDelete') and d.hl_eol then
+        if d and (d.line_hl_group == 'DiffsAdd' or d.line_hl_group == 'DiffsDelete') then
-          line_bgs[mark[2]] = d.hl_group
+          line_bgs[mark[2]] = d.line_hl_group
         end
       end
       assert.is_nil(line_bgs[1])
@@ -946,11 +1062,16 @@ describe('highlight', function()
       highlight.highlight_hunk(bufnr, ns, hunk, default_opts())
 
       local extmarks = get_extmarks(bufnr)
+      local content_clear_count = 0
       for _, mark in ipairs(extmarks) do
         if mark[4] and mark[4].hl_group == 'DiffsClear' then
-          assert.are.equal(2, mark[3])
+          assert.is_true(mark[3] == 0 or mark[3] == 2, 'DiffsClear at unexpected col ' .. mark[3])
+          if mark[3] == 2 then
+            content_clear_count = content_clear_count + 1
+          end
         end
       end
+      assert.are.equal(2, content_clear_count)
       delete_buffer(bufnr)
     end)
 
@@ -1034,8 +1155,8 @@ describe('highlight', function()
       local marker_text = {}
       for _, mark in ipairs(extmarks) do
         local d = mark[4]
-        if d and (d.hl_group == 'DiffsAdd' or d.hl_group == 'DiffsDelete') and d.hl_eol then
+        if d and (d.line_hl_group == 'DiffsAdd' or d.line_hl_group == 'DiffsDelete') then
-          line_bgs[mark[2]] = d.hl_group
+          line_bgs[mark[2]] = d.line_hl_group
         end
         if d and d.number_hl_group then
           gutter_hls[mark[2]] = d.number_hl_group
@@ -1245,6 +1366,467 @@ describe('highlight', function()
       assert.are.equal(0, header_extmarks)
       delete_buffer(bufnr)
     end)
+
+    it('does not apply DiffsClear to header lines for non-quoted diffs', function()
+      local bufnr = create_buffer({
+        'diff --git a/parser.lua b/parser.lua',
+        'index 3e8afa0..018159c 100644',
+        '--- a/parser.lua',
+        '+++ b/parser.lua',
+        '@@ -1,2 +1,3 @@',
+        ' local M = {}',
+        '+local x = 1',
+      })
+
+      local hunk = {
+        filename = 'parser.lua',
+        lang = 'lua',
+        start_line = 5,
+        lines = { ' local M = {}', '+local x = 1' },
+        header_start_line = 1,
+        header_lines = {
+          'diff --git a/parser.lua b/parser.lua',
+          'index 3e8afa0..018159c 100644',
+          '--- a/parser.lua',
+          '+++ b/parser.lua',
+        },
+      }
+
+      highlight.highlight_hunk(bufnr, ns, hunk, default_opts())
+
+      local extmarks = get_extmarks(bufnr)
+      for _, mark in ipairs(extmarks) do
+        local d = mark[4]
+        if d and d.hl_group == 'DiffsClear' and mark[3] == 0 and mark[2] < 4 then
+          error('unexpected DiffsClear on header row ' .. mark[2] .. ' for non-quoted diff')
+        end
+      end
+      delete_buffer(bufnr)
+    end)
+
+    it('preserves diff grammar treesitter on headers for non-quoted diffs', function()
+      local bufnr = create_buffer({
+        'diff --git a/parser.lua b/parser.lua',
+        '--- a/parser.lua',
+        '+++ b/parser.lua',
+        '@@ -1,2 +1,3 @@',
+        ' local M = {}',
+        '+local x = 1',
+      })
+
+      local hunk = {
+        filename = 'parser.lua',
+        lang = 'lua',
+        start_line = 4,
+        lines = { ' local M = {}', '+local x = 1' },
+        header_start_line = 1,
+        header_lines = {
+          'diff --git a/parser.lua b/parser.lua',
+          '--- a/parser.lua',
+          '+++ b/parser.lua',
+        },
+      }
+
+      highlight.highlight_hunk(bufnr, ns, hunk, default_opts())
+
+      local extmarks = get_extmarks(bufnr)
+      local header_ts_count = 0
+      for _, mark in ipairs(extmarks) do
+        local d = mark[4]
+        if mark[2] < 3 and d and d.hl_group and d.hl_group:match('^@.*%.diff$') then
+          header_ts_count = header_ts_count + 1
+        end
+      end
+      assert.is_true(header_ts_count > 0, 'expected diff grammar treesitter on header lines')
+      delete_buffer(bufnr)
+    end)
+
+    it('applies syntax extmarks to combined diff body lines', function()
+      local bufnr = create_buffer({
+        '@@@ -1,2 -1,2 +1,3 @@@',
+        '  local M = {}',
+        '+ local x = 1',
+        ' -local y = 2',
+      })
+
+      local hunk = {
+        filename = 'test.lua',
+        lang = 'lua',
+        prefix_width = 2,
+        start_line = 1,
+        lines = { '  local M = {}', '+ local x = 1', ' -local y = 2' },
+      }
+
+      highlight.highlight_hunk(bufnr, ns, hunk, default_opts())
+
+      local extmarks = get_extmarks(bufnr)
+      local syntax_on_body = 0
+      for _, mark in ipairs(extmarks) do
+        local d = mark[4]
+        if mark[2] >= 1 and d and d.hl_group and d.hl_group:match('^@.*%.lua$') then
+          syntax_on_body = syntax_on_body + 1
+        end
+      end
+      assert.is_true(syntax_on_body > 0, 'expected lua treesitter syntax on combined diff body')
+      delete_buffer(bufnr)
+    end)
+
+    it('applies DiffsClear and per-char diff fg to combined diff body prefixes', function()
+      local bufnr = create_buffer({
+        '@@@',
+        '  unchanged',
+        '+ added',
+        ' -removed',
+        '++both',
+      })
+
+      local hunk = {
+        filename = 'test.lua',
+        lang = 'lua',
+        prefix_width = 2,
+        start_line = 1,
+        lines = { '  unchanged', '+ added', ' -removed', '++both' },
+      }
+
+      highlight.highlight_hunk(bufnr, ns, hunk, default_opts())
+
+      local extmarks = get_extmarks(bufnr)
+      local prefix_clears = {}
+      local plus_marks = {}
+      local minus_marks = {}
+      for _, mark in ipairs(extmarks) do
+        local d = mark[4]
+        if mark[2] >= 1 and d then
+          if d.hl_group == 'DiffsClear' and mark[3] == 0 and d.end_col == 2 then
+            prefix_clears[mark[2]] = true
+          end
+          if d.hl_group == '@diff.plus' and d.priority == 199 then
+            if not plus_marks[mark[2]] then
+              plus_marks[mark[2]] = {}
+            end
+            table.insert(plus_marks[mark[2]], mark[3])
+          end
+          if d.hl_group == '@diff.minus' and d.priority == 199 then
+            if not minus_marks[mark[2]] then
+              minus_marks[mark[2]] = {}
+            end
+            table.insert(minus_marks[mark[2]], mark[3])
+          end
+        end
+      end
+
+      assert.is_true(prefix_clears[1] ~= nil, 'DiffsClear on context prefix')
+      assert.is_true(prefix_clears[2] ~= nil, 'DiffsClear on add prefix')
+      assert.is_true(prefix_clears[3] ~= nil, 'DiffsClear on del prefix')
+      assert.is_true(prefix_clears[4] ~= nil, 'DiffsClear on both-add prefix')
+
+      assert.is_true(plus_marks[2] ~= nil, '@diff.plus on + in "+ added"')
+      assert.are.equal(0, plus_marks[2][1])
+
+      assert.is_true(minus_marks[3] ~= nil, '@diff.minus on - in " -removed"')
+      assert.are.equal(1, minus_marks[3][1])
+
+      assert.is_true(plus_marks[4] ~= nil, '@diff.plus on ++ in "++both"')
+      assert.are.equal(2, #plus_marks[4])
+
+      assert.is_nil(plus_marks[1], 'no @diff.plus on context "  unchanged"')
+      assert.is_nil(minus_marks[1], 'no @diff.minus on context "  unchanged"')
+      delete_buffer(bufnr)
+    end)
+
+    it('applies DiffsClear to headers for combined diffs', function()
+      local bufnr = create_buffer({
+        'diff --combined lua/merge/target.lua',
+        'index abc1234,def5678..ghi9012',
+        '--- a/lua/merge/target.lua',
+        '+++ b/lua/merge/target.lua',
+        '@@@ -1,2 -1,2 +1,3 @@@',
+        '  local M = {}',
+        '+ local x = 1',
+      })
+
+      local hunk = {
+        filename = 'lua/merge/target.lua',
+        lang = 'lua',
+        prefix_width = 2,
+        start_line = 5,
+        lines = { '  local M = {}', '+ local x = 1' },
+        header_start_line = 1,
+        header_lines = {
+          'diff --combined lua/merge/target.lua',
+          'index abc1234,def5678..ghi9012',
+          '--- a/lua/merge/target.lua',
+          '+++ b/lua/merge/target.lua',
+        },
+      }
+
+      highlight.highlight_hunk(bufnr, ns, hunk, default_opts())
+
+      local extmarks = get_extmarks(bufnr)
+      local clear_lines = {}
+      for _, mark in ipairs(extmarks) do
+        local d = mark[4]
+        if d and d.hl_group == 'DiffsClear' and mark[3] == 0 and mark[2] < 4 then
+          clear_lines[mark[2]] = true
+        end
+      end
+      assert.is_true(clear_lines[0] ~= nil, 'DiffsClear on diff --combined line')
+      assert.is_true(clear_lines[1] ~= nil, 'DiffsClear on index line')
+      assert.is_true(clear_lines[2] ~= nil, 'DiffsClear on --- line')
+      assert.is_true(clear_lines[3] ~= nil, 'DiffsClear on +++ line')
+      delete_buffer(bufnr)
+    end)
+
+    it('applies @attribute.diff at syntax priority to @@@ line for combined diffs', function()
+      local bufnr = create_buffer({
+        '@@@ -1,2 -1,2 +1,3 @@@',
+        '  local M = {}',
+        '+ local x = 1',
+      })
+
+      local hunk = {
+        filename = 'test.lua',
+        lang = 'lua',
+        prefix_width = 2,
+        start_line = 1,
+        lines = { '  local M = {}', '+ local x = 1' },
+      }
+
+      highlight.highlight_hunk(bufnr, ns, hunk, default_opts())
+
+      local extmarks = get_extmarks(bufnr)
+      local has_attr = false
+      for _, mark in ipairs(extmarks) do
+        local d = mark[4]
+        if mark[2] == 0 and d and d.hl_group == '@attribute.diff' and (d.priority or 0) >= 199 then
+          has_attr = true
+        end
+      end
+      assert.is_true(has_attr, '@attribute.diff at p>=199 on @@@ line')
+      delete_buffer(bufnr)
+    end)
+
+    it('applies DiffsClear to @@@ line for combined diffs', function()
+      local bufnr = create_buffer({
+        '@@@ -1,2 -1,2 +1,3 @@@',
+        '  local M = {}',
+        '+ local x = 1',
+      })
+
+      local hunk = {
+        filename = 'test.lua',
+        lang = 'lua',
+        prefix_width = 2,
+        start_line = 1,
+        lines = { '  local M = {}', '+ local x = 1' },
+      }
+
+      highlight.highlight_hunk(bufnr, ns, hunk, default_opts())
+
+      local extmarks = get_extmarks(bufnr)
+      local has_at_clear = false
+      for _, mark in ipairs(extmarks) do
+        local d = mark[4]
+        if mark[2] == 0 and d and d.hl_group == 'DiffsClear' and mark[3] == 0 then
+          has_at_clear = true
+        end
+      end
+      assert.is_true(has_at_clear, 'DiffsClear on @@@ line')
+      delete_buffer(bufnr)
+    end)
+
+    it('applies header diff grammar at syntax priority for combined diffs', function()
+      local bufnr = create_buffer({
+        'diff --combined lua/merge/target.lua',
+        'index abc1234,def5678..ghi9012',
+        '--- a/lua/merge/target.lua',
+        '+++ b/lua/merge/target.lua',
+        '@@@ -1,2 -1,2 +1,3 @@@',
+        '  local M = {}',
+        '+ local x = 1',
+      })
+
+      local hunk = {
+        filename = 'lua/merge/target.lua',
+        lang = 'lua',
+        prefix_width = 2,
+        start_line = 5,
+        lines = { '  local M = {}', '+ local x = 1' },
+        header_start_line = 1,
+        header_lines = {
+          'diff --combined lua/merge/target.lua',
+          'index abc1234,def5678..ghi9012',
+          '--- a/lua/merge/target.lua',
+          '+++ b/lua/merge/target.lua',
+        },
+      }
+
+      highlight.highlight_hunk(bufnr, ns, hunk, default_opts())
+
+      local extmarks = get_extmarks(bufnr)
+      local high_prio_diff = {}
+      for _, mark in ipairs(extmarks) do
+        local d = mark[4]
+        if
+          mark[2] < 4
+          and d
+          and d.hl_group
+          and d.hl_group:match('^@.*%.diff$')
+          and (d.priority or 0) >= 199
+        then
+          high_prio_diff[mark[2]] = true
+        end
+      end
+      assert.is_true(high_prio_diff[2] ~= nil, 'diff grammar at p>=199 on --- line')
+      assert.is_true(high_prio_diff[3] ~= nil, 'diff grammar at p>=199 on +++ line')
+      delete_buffer(bufnr)
+    end)
+
+    it('@diff.minus wins over @punctuation.special on combined diff headers', function()
+      local bufnr = create_buffer({
+        'diff --combined lua/merge/target.lua',
+        'index abc1234,def5678..ghi9012',
+        '--- a/lua/merge/target.lua',
+        '+++ b/lua/merge/target.lua',
+        '@@@ -1,2 -1,2 +1,3 @@@',
+        '  local M = {}',
+        '+ local x = 1',
+      })
+
+      local hunk = {
+        filename = 'lua/merge/target.lua',
+        lang = 'lua',
+        prefix_width = 2,
+        start_line = 5,
+        lines = { '  local M = {}', '+ local x = 1' },
+        header_start_line = 1,
+        header_lines = {
+          'diff --combined lua/merge/target.lua',
+          'index abc1234,def5678..ghi9012',
+          '--- a/lua/merge/target.lua',
+          '+++ b/lua/merge/target.lua',
+        },
+      }
+
+      highlight.highlight_hunk(bufnr, ns, hunk, default_opts())
+
+      local extmarks = get_extmarks(bufnr)
+      local minus_prio, punct_prio_minus = 0, 0
+      local plus_prio, punct_prio_plus = 0, 0
+      for _, mark in ipairs(extmarks) do
+        local d = mark[4]
+        if d and d.hl_group then
+          if mark[2] == 2 then
+            if d.hl_group == '@diff.minus.diff' then
+              minus_prio = math.max(minus_prio, d.priority or 0)
+            elseif d.hl_group == '@punctuation.special.diff' then
+              punct_prio_minus = math.max(punct_prio_minus, d.priority or 0)
+            end
+          elseif mark[2] == 3 then
+            if d.hl_group == '@diff.plus.diff' then
+              plus_prio = math.max(plus_prio, d.priority or 0)
+            elseif d.hl_group == '@punctuation.special.diff' then
+              punct_prio_plus = math.max(punct_prio_plus, d.priority or 0)
+            end
+          end
+        end
+      end
+      assert.is_true(
+        minus_prio > punct_prio_minus,
+        '@diff.minus.diff should beat @punctuation.special.diff on --- line'
+      )
+      assert.is_true(
+        plus_prio > punct_prio_plus,
+        '@diff.plus.diff should beat @punctuation.special.diff on +++ line'
+      )
+      delete_buffer(bufnr)
+    end)
+
+    it('applies @keyword.diff on index word for combined diffs', function()
+      local bufnr = create_buffer({
+        'diff --combined lua/merge/target.lua',
+        'index abc1234,def5678..ghi9012',
+        '--- a/lua/merge/target.lua',
+        '+++ b/lua/merge/target.lua',
+        '@@@ -1,2 -1,2 +1,3 @@@',
+        '  local M = {}',
+        '+ local x = 1',
+      })
+
+      local hunk = {
+        filename = 'lua/merge/target.lua',
+        lang = 'lua',
+        prefix_width = 2,
+        start_line = 5,
+        lines = { '  local M = {}', '+ local x = 1' },
+        header_start_line = 1,
+        header_lines = {
+          'diff --combined lua/merge/target.lua',
+          'index abc1234,def5678..ghi9012',
+          '--- a/lua/merge/target.lua',
+          '+++ b/lua/merge/target.lua',
+        },
+      }
+
+      highlight.highlight_hunk(bufnr, ns, hunk, default_opts())
+
+      local extmarks = get_extmarks(bufnr)
+      local has_keyword = false
+      for _, mark in ipairs(extmarks) do
+        local d = mark[4]
+        if
+          mark[2] == 1
+          and d
+          and d.hl_group == '@keyword.diff'
+          and mark[3] == 0
+          and (d.end_col or 0) == 5
+        then
+          has_keyword = true
+        end
+      end
+      assert.is_true(has_keyword, '@keyword.diff at row 1, cols 0-5')
+      delete_buffer(bufnr)
+    end)
+
+    it('applies @constant.diff on result hash for combined diffs', function()
+      local bufnr = create_buffer({
+        'diff --combined lua/merge/target.lua',
+        'index abc1234,def5678..ghi9012',
+        '--- a/lua/merge/target.lua',
+        '+++ b/lua/merge/target.lua',
+        '@@@ -1,2 -1,2 +1,3 @@@',
+        '  local M = {}',
+        '+ local x = 1',
+      })
+
+      local hunk = {
+        filename = 'lua/merge/target.lua',
+        lang = 'lua',
+        prefix_width = 2,
+        start_line = 5,
+        lines = { '  local M = {}', '+ local x = 1' },
+        header_start_line = 1,
+        header_lines = {
+          'diff --combined lua/merge/target.lua',
+          'index abc1234,def5678..ghi9012',
+          '--- a/lua/merge/target.lua',
+          '+++ b/lua/merge/target.lua',
+        },
+      }
+
+      highlight.highlight_hunk(bufnr, ns, hunk, default_opts())
+
+      local extmarks = get_extmarks(bufnr)
+      local has_constant = false
+      for _, mark in ipairs(extmarks) do
+        local d = mark[4]
+        if mark[2] == 1 and d and d.hl_group == '@constant.diff' and (d.priority or 0) >= 199 then
+          has_constant = true
+        end
+      end
+      assert.is_true(has_constant, '@constant.diff on result hash')
+      delete_buffer(bufnr)
+    end)
   end)
 
   describe('extmark priority', function()

spec/integration_spec.lua

@@ -127,6 +127,110 @@ describe('integration', function()
     end)
   end)
 
+  describe('ft_retry_pending', function()
+    before_each(function()
+      rawset(vim.fn, 'did_filetype', function()
+        return 1
+      end)
+      require('diffs.parser')._test.ft_lang_cache = {}
+    end)
+
+    after_each(function()
+      rawset(vim.fn, 'did_filetype', nil)
+    end)
+
+    it('sets ft_retry_pending when nil-ft hunks detected under did_filetype', function()
+      local bufnr = create_buffer({
+        'diff --git a/app.conf b/app.conf',
+        '@@ -1,2 +1,2 @@',
+        ' server {',
+        '-    listen 80;',
+        '+    listen 8080;',
+      })
+      diffs.attach(bufnr)
+      local entry = diffs._test.hunk_cache[bufnr]
+      assert.is_not_nil(entry)
+      assert.is_nil(entry.hunks[1].ft)
+      assert.is_true(diffs._test.ft_retry_pending[bufnr] == true)
+      delete_buffer(bufnr)
+    end)
+
+    it('clears ft_retry_pending after scheduled callback fires', function()
+      local bufnr = create_buffer({
+        'diff --git a/app.conf b/app.conf',
+        '@@ -1,2 +1,2 @@',
+        ' server {',
+        '-    listen 80;',
+        '+    listen 8080;',
+      })
+      diffs.attach(bufnr)
+      assert.is_true(diffs._test.ft_retry_pending[bufnr] == true)
+
+      local done = false
+      vim.schedule(function()
+        done = true
+      end)
+      vim.wait(1000, function()
+        return done
+      end)
+
+      assert.is_nil(diffs._test.ft_retry_pending[bufnr])
+      delete_buffer(bufnr)
+    end)
+
+    it('invalidates cache after scheduled callback fires', function()
+      local bufnr = create_buffer({
+        'diff --git a/app.conf b/app.conf',
+        '@@ -1,2 +1,2 @@',
+        ' server {',
+        '-    listen 80;',
+        '+    listen 8080;',
+      })
+      diffs.attach(bufnr)
+      local tick_after_attach = diffs._test.hunk_cache[bufnr].tick
+      assert.is_true(tick_after_attach >= 0)
+
+      local done = false
+      vim.schedule(function()
+        done = true
+      end)
+      vim.wait(1000, function()
+        return done
+      end)
+
+      local entry = diffs._test.hunk_cache[bufnr]
+      assert.are.equal(-1, entry.tick)
+      assert.is_true(entry.pending_clear)
+      delete_buffer(bufnr)
+    end)
+
+    it('does not set ft_retry_pending when did_filetype() is zero', function()
+      rawset(vim.fn, 'did_filetype', nil)
+      local bufnr = create_buffer({
+        'diff --git a/test.sh b/test.sh',
+        '@@ -1,2 +1,3 @@',
+        ' #!/usr/bin/env bash',
+        '-old line',
+        '+new line',
+      })
+      diffs.attach(bufnr)
+      assert.is_falsy(diffs._test.ft_retry_pending[bufnr])
+      delete_buffer(bufnr)
+    end)
+
+    it('does not set ft_retry_pending for files with resolvable ft', function()
+      local bufnr = create_buffer({
+        'M test.lua',
+        '@@ -1,1 +1,2 @@',
+        ' local x = 1',
+        '+local y = 2',
+      })
+      diffs.attach(bufnr)
+      assert.is_falsy(diffs._test.ft_retry_pending[bufnr])
+      delete_buffer(bufnr)
+    end)
+  end)
+
   describe('extmarks from highlight pipeline', function()
     it('DiffsAdd background applied to + lines', function()
       local bufnr = create_buffer({
@@ -145,7 +249,7 @@ describe('integration', function()
       local extmarks = get_extmarks(bufnr, ns)
       local has_diff_add = false
       for _, mark in ipairs(extmarks) do
-        if mark[4] and mark[4].hl_group == 'DiffsAdd' then
+        if mark[4] and mark[4].line_hl_group == 'DiffsAdd' then
           has_diff_add = true
           break
         end
@@ -171,7 +275,7 @@ describe('integration', function()
       local extmarks = get_extmarks(bufnr, ns)
       local has_diff_delete = false
       for _, mark in ipairs(extmarks) do
-        if mark[4] and mark[4].hl_group == 'DiffsDelete' then
+        if mark[4] and mark[4].line_hl_group == 'DiffsDelete' then
           has_diff_delete = true
           break
         end
@@ -198,10 +302,10 @@ describe('integration', function()
       local has_add = false
       local has_delete = false
       for _, mark in ipairs(extmarks) do
-        if mark[4] and mark[4].hl_group == 'DiffsAdd' then
+        if mark[4] and mark[4].line_hl_group == 'DiffsAdd' then
           has_add = true
         end
-        if mark[4] and mark[4].hl_group == 'DiffsDelete' then
+        if mark[4] and mark[4].line_hl_group == 'DiffsDelete' then
           has_delete = true
         end
       end
@@ -230,8 +334,8 @@ describe('integration', function()
       local line_bgs = {}
       for _, mark in ipairs(extmarks) do
         local d = mark[4]
-        if d and (d.hl_group == 'DiffsAdd' or d.hl_group == 'DiffsDelete') and d.hl_eol then
+        if d and (d.line_hl_group == 'DiffsAdd' or d.line_hl_group == 'DiffsDelete') then
-          line_bgs[mark[2]] = d.hl_group
+          line_bgs[mark[2]] = d.line_hl_group
         end
       end
       assert.is_nil(line_bgs[1])
@@ -313,10 +417,10 @@ describe('integration', function()
       local del_lines = {}
       for _, mark in ipairs(extmarks) do
         local d = mark[4]
-        if d and d.hl_group == 'DiffsAdd' and d.hl_eol then
+        if d and d.line_hl_group == 'DiffsAdd' then
           add_lines[mark[2]] = true
         end
-        if d and d.hl_group == 'DiffsDelete' and d.hl_eol then
+        if d and d.line_hl_group == 'DiffsDelete' then
           del_lines[mark[2]] = true
         end
       end

spec/parser_spec.lua

@@ -163,10 +163,10 @@ describe('parser', function()
       end
     end)
 
-    it('stops hunk at blank line', function()
+    it('stops hunk at blank line when remaining counts exhausted', function()
       local bufnr = create_buffer({
         'M test.lua',
-        '@@ -1,2 +1,3 @@',
+        '@@ -1,1 +1,2 @@',
         ' local x = 1',
         '+local y = 2',
         '',
@@ -391,6 +391,29 @@ describe('parser', function()
       vim.fn.delete(repo_root, 'rf')
     end)
 
+    it('detects filetype for .sh files when did_filetype() is non-zero', function()
+      rawset(vim.fn, 'did_filetype', function()
+        return 1
+      end)
+
+      parser._test.ft_lang_cache = {}
+      local bufnr = create_buffer({
+        'diff --git a/test.sh b/test.sh',
+        '@@ -1,3 +1,4 @@',
+        ' #!/usr/bin/env bash',
+        ' set -euo pipefail',
+        '-echo "running tests..."',
+        '+echo "running tests with coverage..."',
+      })
+      local hunks = parser.parse_buffer(bufnr)
+
+      assert.are.equal(1, #hunks)
+      assert.are.equal('test.sh', hunks[1].filename)
+      assert.are.equal('sh', hunks[1].ft)
+      delete_buffer(bufnr)
+      rawset(vim.fn, 'did_filetype', nil)
+    end)
+
     it('extracts file line numbers from @@ header', function()
       local bufnr = create_buffer({
         'M lua/test.lua',
@@ -506,7 +529,8 @@ describe('parser', function()
       assert.are.equal(1, #hunks)
       assert.are.equal(1, hunks[1].file_new_start)
       assert.are.equal(9, hunks[1].file_new_count)
-      assert.is_nil(hunks[1].file_old_start)
+      assert.are.equal(1, hunks[1].file_old_start)
+      assert.are.equal(3, hunks[1].file_old_count)
       delete_buffer(bufnr)
     end)