Agentic UI: Remove unused starred flag from AI chat sessions

[bcotrim]

Related issues

• Fixes STU-2061

How AI was used in this PR

Claude traced every reference to the starred session flag across the codebase, removed the dead plumbing, updated the tests, and ran lint/typecheck/tests. Changes were reviewed and the archive flow was manually tested.

Proposed Changes

The star/unstar UI for chat conversations was removed in #4191, which left the starred session-metadata flag as dead plumbing: nothing could set it and nothing displayed it. This PR retires the flag end-to-end — from the shared-config schema, session types and hydration, the IPC handler, the hosted/local PATCH endpoints, and the UI data layer.

• Starring was already unreachable, so removing it has no user-visible impact.
• No config migration needed: the shared-config schema is loose, so existing shared.json files with leftover starred entries still parse fine; the stale keys are simply ignored and go away when the chat is deleted.
• Based on review feedback: archiving the chat you're currently viewing now opens a new chat instead of leaving you inside the archived conversation.

Testing Instructions

• Search the codebase for starred — no references to the removed feature remain.
• In the agentic UI, open a chat for a site, archive another chat from the Chat history menu, and confirm it moves to the "Archived chats" dialog.
• Archive the chat you're currently on — a new chat should open instead of staying on the archived one.
• If your ~/.studio/shared.json has old "starred" entries, everything keeps working; they're just ignored.

Pre-merge Checklist

• Have you checked for TypeScript, React or other console errors?

🤖 Generated with Claude Code

[wpmobilebot]

📊 Performance Test Results

Comparing b1f2aff vs trunk

app-size

Metric	trunk	b1f2aff	Diff	Change
App Size (Mac)	1353.02 MB	1353.02 MB	0.00 MB	⚪ 0.0%

site-editor

Metric	trunk	b1f2aff	Diff	Change
load	1086 ms	1061 ms	25 ms	⚪ 0.0%

site-startup

Metric	trunk	b1f2aff	Diff	Change
siteCreation	7037 ms	6987 ms	50 ms	🟢 -0.7%
siteStartup	2356 ms	2365 ms	+9 ms	⚪ 0.0%

---

Results are median values from multiple test runs.

Legend: 🟢 Improvement (faster) | 🔴 Regression (slower) | ⚪ No change (<50ms diff)

[katinthehatsite]

I did not see any issues specifically with starred convesations cleanup and it worked as expected on my end 👍

Something that I found a bit strange (perhaps it is not directly related to this PR), is that when you archive a chat, you remain on it instead of a new chat opening. I think this would be the behaviour I expect when something is archived. What do you think?

[bcotrim]

I did not see any issues specifically with starred convesations cleanup and it worked as expected on my end 👍

Something that I found a bit strange (perhaps it is not directly related to this PR), is that when you archive a chat, you remain on it instead of a new chat opening. I think this would be the behaviour I expect when something is archived. What do you think?

That makes sense, nice catch! 👍

[bcotrim]

I did not see any issues specifically with starred convesations cleanup and it worked as expected on my end 👍

Something that I found a bit strange (perhaps it is not directly related to this PR), is that when you archive a chat, you remain on it instead of a new chat opening. I think this would be the behaviour I expect when something is archived. What do you think?

@katinthehatsite I added it in 37e3f02

[sejas]

Thanks for cleaning up the starred logic. We might be leaving existing saved starred sessions in shared.json, but I think that's okay since almost no one has used that feature yet.

[bcotrim]

Thanks for cleaning up the starred logic. We might be leaving existing saved starred sessions in shared.json, but I think that's okay since almost no one has used that feature yet.

Agreed, that was intentional. Adding some logic/migration isn't worth it for such a small user cleanup, imo