feat(conflict): add virtual text formatting and action lines (#101)

## Problem

Conflict resolution virtual text only showed plain "current" /
"incoming"
labels with no keymap hints. Users had no way to discover available
resolution keymaps without reading docs.

## Solution

Default virtual text labels now include keymap hints: `(current — doo)`
and
`(incoming — dot)`. A new `format_virtual_text` config option lets users
customize or hide labels entirely. A new `show_actions` option (off by
default) renders a codelens-style action line above each `<<<<<<<`
marker
listing all enabled resolution keymaps. Merge diff views also gain hunk
hints on `@@` header lines showing available keymaps.

New config fields: `conflict.format_virtual_text` (function|nil),
`conflict.show_actions` (boolean). New highlight group:
`DiffsConflictActions`.

lua/diffs/conflict.lua

@@ -92,6 +92,17 @@ local function parse_buffer(bufnr)
   return M.parse(lines)
 end
 
+---@param side string
+---@param config diffs.ConflictConfig
+---@return string?
+local function get_virtual_text_label(side, config)
+  if config.format_virtual_text then
+    local keymap = side == 'ours' and config.keymaps.ours or config.keymaps.theirs
+    return config.format_virtual_text(side, keymap)
+  end
+  return side == 'ours' and 'current' or 'incoming'
+end
+
 ---@param bufnr integer
 ---@param regions diffs.ConflictRegion[]
 ---@param config diffs.ConflictConfig
@@ -107,10 +118,37 @@ local function apply_highlights(bufnr, regions, config)
     })
 
     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',
-      })
+      local ours_label = get_virtual_text_label('ours', config)
+      if ours_label then
+        pcall(vim.api.nvim_buf_set_extmark, bufnr, ns, region.marker_ours, 0, {
+          virt_text = { { ' (' .. ours_label .. ')', 'DiffsConflictMarker' } },
+          virt_text_pos = 'eol',
+        })
+      end
+    end
+
+    if config.show_actions then
+      local parts = {}
+      local actions = {
+        { 'Current', config.keymaps.ours },
+        { 'Incoming', config.keymaps.theirs },
+        { 'Both', config.keymaps.both },
+        { 'None', config.keymaps.none },
+      }
+      for _, action in ipairs(actions) do
+        if action[2] then
+          if #parts > 0 then
+            table.insert(parts, { ' \226\148\130 ', 'DiffsConflictActions' })
+          end
+          table.insert(parts, { ('%s (%s)'):format(action[1], action[2]), 'DiffsConflictActions' })
+        end
+      end
+      if #parts > 0 then
+        pcall(vim.api.nvim_buf_set_extmark, bufnr, ns, region.marker_ours, 0, {
+          virt_lines = { parts },
+          virt_lines_above = true,
+        })
+      end
     end
 
     for line = region.ours_start, region.ours_end - 1 do
@@ -176,10 +214,13 @@ local function apply_highlights(bufnr, regions, config)
     })
 
     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',
-      })
+      local theirs_label = get_virtual_text_label('theirs', config)
+      if theirs_label then
+        pcall(vim.api.nvim_buf_set_extmark, bufnr, ns, region.marker_theirs, 0, {
+          virt_text = { { ' (' .. theirs_label .. ')', 'DiffsConflictMarker' } },
+          virt_text_pos = 'eol',
+        })
+      end
     end
   end
 end

lua/diffs/init.lua

@@ -41,6 +41,8 @@
 ---@field enabled boolean
 ---@field disable_diagnostics boolean
 ---@field show_virtual_text boolean
+---@field format_virtual_text? fun(side: string, keymap: string|false): string?
+---@field show_actions boolean
 ---@field keymaps diffs.ConflictKeymaps
 
 ---@class diffs.Config
@@ -128,6 +130,7 @@ local default_config = {
     enabled = true,
     disable_diagnostics = true,
     show_virtual_text = true,
+    show_actions = false,
     keymaps = {
       ours = 'doo',
       theirs = 'dot',
@@ -276,6 +279,7 @@ local function compute_highlight_groups()
   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, 'DiffsConflictActions', { default = true, fg = 0x808080 })
   vim.api.nvim_set_hl(
     0,
     'DiffsConflictOursNr',
@@ -390,6 +394,8 @@ local function init()
       ['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.format_virtual_text'] = { opts.conflict.format_virtual_text, 'function', true },
+      ['conflict.show_actions'] = { opts.conflict.show_actions, 'boolean', true },
       ['conflict.keymaps'] = { opts.conflict.keymaps, 'table', true },
     })
 

lua/diffs/merge.lua

@@ -338,6 +338,43 @@ function M.goto_prev(bufnr)
   vim.api.nvim_win_set_cursor(0, { candidates[#candidates].start_line + 1, 0 })
 end
 
+---@param bufnr integer
+---@param config diffs.ConflictConfig
+local function apply_hunk_hints(bufnr, config)
+  if not config.show_virtual_text then
+    return
+  end
+
+  local hunks = M.parse_hunks(bufnr)
+  for _, hunk in ipairs(hunks) do
+    if M.is_resolved(bufnr, hunk.index) then
+      add_resolved_virtual_text(bufnr, hunk)
+    else
+      local parts = {}
+      local actions = {
+        { 'current', config.keymaps.ours },
+        { 'incoming', config.keymaps.theirs },
+        { 'both', config.keymaps.both },
+        { 'none', config.keymaps.none },
+      }
+      for _, action in ipairs(actions) do
+        if action[2] then
+          if #parts > 0 then
+            table.insert(parts, { ' | ', 'Comment' })
+          end
+          table.insert(parts, { ('%s: %s'):format(action[2], action[1]), 'Comment' })
+        end
+      end
+      if #parts > 0 then
+        pcall(vim.api.nvim_buf_set_extmark, bufnr, ns, hunk.start_line, 0, {
+          virt_text = parts,
+          virt_text_pos = 'eol',
+        })
+      end
+    end
+  end
+end
+
 ---@param bufnr integer
 ---@param config diffs.ConflictConfig
 function M.setup_keymaps(bufnr, config)
@@ -358,6 +395,8 @@ function M.setup_keymaps(bufnr, config)
     end
   end
 
+  apply_hunk_hints(bufnr, config)
+
   vim.api.nvim_create_autocmd('BufWipeout', {
     buffer = bufnr,
     callback = function()