Hooks: permission_mode never reports "plan" during a Plan-mode turn

What version of Codex CLI is running?

codex-cli 0.153.2

What subscription do you have?

Pro

Which model were you using?

gpt-5.6-sol

What platform is your computer?

macOS 26.6.2, arm64

What terminal emulator and version are you using (if applicable)?

agterm

Codex doctor report

It's clean

What issue are you seeing?

hook can't tell it's in Plan mode. The docs list permission_mode values as "default", "acceptEdits", "plan", "dontAsk", "bypassPermissions", and since there's no separate collaboration-mode field for hooks, "plan" is the only advertised way to know. But in a real Plan-mode turn the field carries the approval policy instead.

Here's a Stop payload from a turn that produced a complete <proposed_plan> block:

  {
    "keys": ["cwd", "hook_event_name", "last_assistant_message", "model",
             "permission_mode", "session_id", "stop_hook_active",
             "transcript_path", "turn_id"],
    "permission_mode": "default",
    "hook_event_name": "Stop",
    "stop_hook_active": false,
    "last_assistant_message": null
  }

permission_mode is "default". The session was definitely in Plan mode - the same turn's transcript entry carries collaboration_mode_kind, and the assistant message has a complete <proposed_plan> block.

What steps can reproduce the bug?

1. Register stop hook that dumps its stdin, e.g. command = "tee -a /tmp/stop-events.jsonl >/dev/null", and trust it via /hooks
2. /plan to switch to Plan mode
3. Ask for anything that produces a plan and let the turn finish
4. cat /tmp/stop-events.jsonl — permission_mode is the approval policy, never "plan"

What is the expected behavior?

permission_mode returns "plan" on a Plan-mode turn

Additional information

No response

Start by tracing how the Stop hook payload is constructed and how permission_mode is populated or serialized. Compare that value with the session transcript's collaboration_mode_kind during the documented /plan reproduction. Done means a Plan-mode turn reports permission_mode as "plan" while the existing approval-policy values remain correct.