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

Problem: when git hits a merge conflict, users stare at raw <<<<<<<
markers with broken treesitter and noisy LSP diagnostics. Existing
solutions (git-conflict.nvim) use their own highlighting rather than
integrating with diffs.nvim's color blending pipeline.

Solution: add conflict.lua module that detects <<<<<<</=======/>>>>>>>
markers (with diff3 ||||||| support), highlights ours/theirs/base
regions with blended DiffsConflict* highlight groups, provides
resolution keymaps (doo/dot/dob/don) and navigation (]x/[x),
suppresses diagnostics while markers are present, and auto-detaches
when all conflicts are resolved. Fires DiffsConflictResolved user
event on last resolution.

lua/diffs/conflict.lua

@@ -0,0 +1,457 @@
+---@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.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'
+  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
+    M.detach(bufnr)
+    vim.api.nvim_exec_autocmds('User', { pattern = 'DiffsConflictResolved' })
+    return
+  end
+  apply_highlights(bufnr, regions, config)
+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
+
+  if km.ours then
+    vim.keymap.set('n', km.ours, function()
+      M.resolve_ours(bufnr, config)
+    end, { buffer = bufnr })
+  end
+  if km.theirs then
+    vim.keymap.set('n', km.theirs, function()
+      M.resolve_theirs(bufnr, config)
+    end, { buffer = bufnr })
+  end
+  if km.both then
+    vim.keymap.set('n', km.both, function()
+      M.resolve_both(bufnr, config)
+    end, { buffer = bufnr })
+  end
+  if km.none then
+    vim.keymap.set('n', km.none, function()
+      M.resolve_none(bufnr, config)
+    end, { buffer = bufnr })
+  end
+  if km.next then
+    vim.keymap.set('n', km.next, function()
+      M.goto_next(bufnr)
+    end, { buffer = bufnr })
+  end
+  if km.prev then
+    vim.keymap.set('n', km.prev, function()
+      M.goto_prev(bufnr)
+    end, { buffer = bufnr })
+  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.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/init.lua

@@ -29,12 +29,27 @@
 ---@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)
@@ -109,6 +124,19 @@ local default_config = {
     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
@@ -231,6 +259,37 @@ local function compute_highlight_groups()
   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)
@@ -324,6 +383,30 @@ 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
@@ -488,4 +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

plugin/diffs.lua

@@ -30,6 +30,15 @@ vim.api.nvim_create_autocmd('BufReadCmd', {
   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()

spec/conflict_spec.lua

@@ -0,0 +1,655 @@
+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('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)