ExitPlanMode approval card shows stale plan content within a session

Description
Within a single session, the plan approval card shown by ExitPlanMode sometimes displays outdated plan content that doesn't match what was actually just written to the plan file.

Steps to reproduce

1. In plan mode, write a plan to the plan file, then edit/rewrite it multiple times in the same session.
2. Call ExitPlanMode to request approval.
3. The approval card shown to the user displays an older version of the plan, not the latest content on disk.

Expected behavior
The approval card should always reflect the current contents of the plan file at the moment ExitPlanMode is called.

Actual behavior
The card sometimes shows stale content from an earlier edit.

Scope / notes

• Appears to be scoped to a specific session — a fresh session with the same plan-file-editing pattern rendered the card correctly.
• Workaround: approve directly via chat text instead of relying on the tool's approval UI when this happens.
• Platform: Windows 11, working directory not a git repo (C:\).