fix(conflict): keep TextChanged autocmd alive after resolution

Problem: resolving the last conflict called M.detach(), which cleared
attached_buffers[bufnr]. The TextChanged callback then returned true,
permanently deleting the autocmd. Undo restored conflict markers but
nothing re-highlighted or re-suppressed diagnostics.

Solution: inline the cleanup in refresh() instead of calling detach().
Keep attached_buffers set so the autocmd survives. Re-suppress
diagnostics when conflicts reappear after undo.

lua/diffs/conflict.lua

@@ -214,11 +214,19 @@ end
 local function refresh(bufnr, config)
   local regions = parse_buffer(bufnr)
   if #regions == 0 then
-    M.detach(bufnr)
+    vim.api.nvim_buf_clear_namespace(bufnr, ns, 0, -1)
+    if diagnostics_suppressed[bufnr] then
+      pcall(vim.diagnostic.enable, true, { bufnr = bufnr })
+      diagnostics_suppressed[bufnr] = nil
+    end
     vim.api.nvim_exec_autocmds('User', { pattern = 'DiffsConflictResolved' })
     return
   end
   apply_highlights(bufnr, regions, config)
+  if config.disable_diagnostics and not diagnostics_suppressed[bufnr] then
+    pcall(vim.diagnostic.enable, false, { bufnr = bufnr })
+    diagnostics_suppressed[bufnr] = true
+  end
 end
 
 ---@param bufnr integer

spec/conflict_spec.lua

@@ -631,6 +631,39 @@ describe('conflict', function()
       helpers.delete_buffer(bufnr)
     end)
 
+    it('re-highlights when markers return after resolution', function()
+      local bufnr = create_file_buffer({
+        '<<<<<<< HEAD',
+        'local x = 1',
+        '=======',
+        'local x = 2',
+        '>>>>>>> feature',
+      })
+      vim.api.nvim_set_current_buf(bufnr)
+      local cfg = default_config()
+      conflict.attach(bufnr, cfg)
+
+      assert.is_true(#get_extmarks(bufnr) > 0)
+
+      vim.api.nvim_win_set_cursor(0, { 2, 0 })
+      conflict.resolve_ours(bufnr, cfg)
+      assert.are.equal(0, #get_extmarks(bufnr))
+
+      vim.api.nvim_buf_set_lines(bufnr, 0, -1, false, {
+        '<<<<<<< HEAD',
+        'local x = 1',
+        '=======',
+        'local x = 2',
+        '>>>>>>> feature',
+      })
+      vim.api.nvim_exec_autocmds('TextChanged', { buffer = bufnr })
+
+      assert.is_true(#get_extmarks(bufnr) > 0)
+
+      conflict.detach(bufnr)
+      helpers.delete_buffer(bufnr)
+    end)
+
     it('detaches after last conflict resolved', function()
       local bufnr = create_file_buffer({
         '<<<<<<< HEAD',