exit_plan_mode hook regression caused by PR 22737

[tbastos]

What happened?

The current docs suggest using a hook to auto-archive plan files: https://geminicli.com/docs/cli/plan-mode/#example-archive-approved-plans-to-gcs-aftertool

This is no longer possible since plan_path (abs path) was replaced by plan_filename (a filename like "plan.md") in #22737 . The hook script no longer receives sufficient data to resolve the path to the plan file by itself (based on the input JSON and env vars), unless it resorts to a hack such as parsing the returnDisplay message.

What did you expect to happen?

The exit_plan_mode hook script should be able to easily resolve the path to the plan file based on the input JSON.

Client information

Client Information

Run gemini to enter the interactive CLI, then run the /about command.

> /about
| CLI Version                            0.36.0-nightly.20260317.2f90b4653-git.e77b22e                            │
│ Git Commit                             e77b22e                                                                  │
│ Model                                  gemini-3.1-pro-preview                                                   │
│ Sandbox                                no sandbox                                                               │
│ OS                                     linux                                                                    │
│ Auth Method                            gemini-api-key    

Login information

No response

Anything else we need to know?

No response