fix: use :startinsert instead of feedkeys to switch to terminal mode

If user has their own `startinsert`, e.g. in the following case,
`startinsert` is trigger by `:term`, but later fzf term is focused.
```
nvim \
  +"au TermOpen * startinsert" \
  +"term" \
  +"lua vim.defer_fn(function() vim.cmd [[FzfLua files]] end, 100)"
```
Technically user should not `startinsert` on an incorrect window, but
currently there's no way to avoid it since builtin `startinsert` seems
defered but `nvim_get_mode` is fast (return actual mode immediately).

Author: phanen

lua/fzf-lua/fzf.lua

@@ -222,6 +222,7 @@ function M.raw_fzf(contents, fzf_cli_args, opts)
       vim.keymap.set("t", "<C-c>", "<Esc>", { buffer = 0 })
     end
 
+    vim.api.nvim_create_autocmd("TermOpen", { once = true, buffer = 0, command = "startinsert" })
     -- A more robust way of entering TERMINAL mode "t". We had quite a few issues
     -- sending `feedkeys|startinsert` after the term job is started, this approach
     -- seems more consistent as it triggers when entering terminal normal mode "nt"
@@ -333,14 +334,8 @@ function M.raw_fzf(contents, fzf_cli_args, opts)
   -- fzf-tmux spawns outside neovim, don't set filetype/insert mode
   if not opts.is_fzf_tmux then
     vim.bo.filetype = "fzf"
-
     -- See note in "ModeChanged" above
-    if vim.api.nvim_get_mode().mode == "t" then
-      -- Called from another fzf-win most likely
-      utils.feed_keys_termcodes("i")
-    else
-      vim.cmd [[startinsert]]
-    end
+    -- utils.ensure_startinsert()
   end
 
   return coroutine.yield()

lua/fzf-lua/utils.lua

@@ -1317,6 +1317,26 @@ function M.setmetatable__gc(t, mt)
   return setmetatable(t, mt)
 end
 
+---@param retry integer?
+---@param timeout integer?
+function M.ensure_startinsert(retry, timeout)
+  local bufnr = vim.api.nvim_get_current_buf()
+  local function ensure_startinsert(_retry, _timeout)
+    -- abort for some reason we switch to another buffer
+    if vim.api.nvim_get_current_buf() ~= bufnr then return end
+    if vim.api.nvim_get_mode().mode ~= "t" or retry == 0 then
+      vim.cmd [[startinsert]]
+      return
+    end
+    -- Called from another fzf-win most likely
+    -- don't startinsert until we enter new terminal mode
+    return vim.defer_fn(function()
+      return ensure_startinsert(_retry - 1, math.min(100, _timeout * 2))
+    end, _timeout)
+  end
+  return ensure_startinsert(retry or 5, timeout or 10)
+end
+
 --- Checks if treesitter parser for language is installed
 ---@param lang string
 function M.has_ts_parser(lang)

tests/file/ui_spec.lua

@@ -206,4 +206,25 @@ T["files()"]["preview should work after chdir #1864"] = function()
   child.expect_screen_lines(screen_opts)
 end
 
+T["files()"]["perioldly reset mode"] = function()
+  child.cmd [[exe 'au TermOpen * startinsert' | term]]
+  sleep(10)
+  child.lua [=[
+    FzfLua.files {
+      cwd_prompt = false,
+      fzf_opts = { ["--no-info"] = "", ["--info"] = false },
+      query = "foo",
+    }
+  ]=]
+  child.wait_until(function() return child.lua_get([[_G._fzf_load_called]]) == true end)
+  -- child.expect_screen_lines({ start_line = 1, end_line = 3 })
+  -- print("\n")
+  -- print(child.get_screen_lines({ start_line = 1, end_line = 3 }))
+  child.assert_screen_lines([[
+       ╭─────────────────── Files  h ────────────────────╮
+       │> foo                                            │
+       │──────────────────────────────────────────────── │
+ ]], { start_line = 3, end_line = 5 })
+end
+
 return T