fix:diff panel doesnt collapse

[Heinrich-XIAO]

What Changed

This PR fixes the diff panel so it can be closed again while keeping normal diff search-param retention behavior.

Why

The chat route was re-retaining diff=1 during close navigations, which caused the diff panel to immediately reopen instead of collapsing.

UI Changes

N/A The expected behaviour was already working before, but it was broken a few days ago, so this is the PR to fix it.

Checklist

• This PR is small and focused
• I explained what changed and why
• N/A I included before/after screenshots for any UI changes
• N/A I included a video for animation/interaction changes\

Note

Fix collapsing diff panel by replacing diff param removal with a clearDiff signal

• Previously, closing the diff panel removed the diff search param, but retainSearchParams would immediately re-add it on the next navigation, preventing the panel from actually closing.
• Closing the diff now sets clearDiff=1 in the URL instead of unsetting diff. A new retainDiffUnlessCleared middleware in _chat.$threadId.tsx carries the diff param forward across navigations unless clearDiff is present.
• After the middleware processes the signal, stripSearchParams(["clearDiff"]) removes clearDiff from the final URL so it doesn't persist.

^{Macroscope summarized b71fc43.}

[coderabbitai]

Important

Review skipped

Auto reviews are disabled on this repository. Please check the settings in the CodeRabbit UI or the .coderabbit.yaml file in this repository. To trigger a single review, invoke the @coderabbitai review command.

⚙️ Run configuration

Configuration used: Repository UI

Review profile: CHILL

Plan: Pro

Run ID: 2388b2d0-6660-46fc-9125-6cfe4fd707a2

You can disable this status message by setting the reviews.review_status to false in the CodeRabbit configuration file.

Use the checkbox below for a quick retry:

• 🔍 Trigger review

✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Post copyable unit tests in a comment

📝 Coding Plan

• Generate coding plan for human review comments

---

Thanks for using CodeRabbit! It's free for OSS, and your support helps us grow. If you like it, consider giving us a shout-out.

❤️ Share

• X
• Mastodon
• Reddit
• LinkedIn

_{Comment @coderabbitai help to get the list of available commands and usage tips.}

Tip

Migrating from UI to YAML configuration.

Use the @coderabbitai configuration command in a PR comment to get a dump of all your UI settings in YAML format. You can then edit this YAML file and upload it to the root of your repository to configure CodeRabbit programmatically.

[juliusmarminge]

should already be fixed on main and coming out in the next release. diff: undefined was the fix from #937