[BUG] Stale plan preview in claude desktop

### Preflight Checklist

- [x] I have searched [existing issues](https://github.com/anthropics/claude-code/issues?q=is%3Aissue%20state%3Aopen%20label%3Abug) and this hasn't been reported yet
- [x] This is a single bug report (please file separate reports for different bugs)
- [x] I am using the latest version of Claude Code

### What's Wrong?

Desktop app on latest osx.

When claude prepares a plan it writes it to ~/.claude/plans/randomname.md

Subsequent changes to that plan via the revise plan action or instructing it directly do not change the plan in the preview pane in the desktop app. The actual file is changes and the changes are visible in the. change diffs in the conversation, but clicking on them to expand the file opens the original cached plan, never the latest ones leading to confusion and inability to provide feedback.

I assume the same thing happens to other. claude produced artifacts like random html docs or charts but that hasn't been verified or reproduced.

### What Should Happen?

Every change to the plan file or anything else in the preview pane should reflect the latest state of the underlying file.

### Error Messages/Logs

```shell

```

### Steps to Reproduce

1. Start a planning session.
2. Iterate on it use revise plan etc.
3. open the plan in the pewview pane by clicking on on the porposed plan -> you will see the original first proposal, none of the later iterations are there.

### Claude Model

None

### Is this a regression?

I don't know

### Last Working Version

_No response_

### Claude Code Version

Claude 1.34493.1 (255293) 2026-08-21T02:05:20.000Z (claude for mac)

### Platform

Anthropic API

### Operating System

macOS

### Terminal/Shell

Other

### Additional Information

_No response_

Start by reproducing the issue with a planning session and the file at ~/.claude/plans/randomname.md. Compare the file and conversation diff after using revise plan with the content shown when the proposed plan is opened in the desktop preview pane. Done means the preview reflects every subsequent change to the underlying plan file.

索引モデルが issue の本文から書いたものです。