[Bug]: iOS: Opening Thread while in Compaction

[tristinfinch]

Before submitting

• I searched existing issues and did not find a duplicate.
• I included enough detail to reproduce or investigate the problem.

Area

apps/web

Steps to reproduce

1. Attempt to open a thread while it is compacting
2. thread does not open
3. can no longer access other thread.

App has to be quit and re opened to function.

Expected behavior

Opens thread with something indicating compaction in progress

Actual behavior

App locks and becomes unusable.

Impact

Major degradation or frequent failure

Version or commit

No response

Environment

No response

Logs or stack traces

Screenshots, recordings, or supporting files

No response

Workaround

No response

[juliusmarminge]

Triage

Opening a compacting thread on iOS fails, then the rest of the app stops responding until force-quit. The issue form says apps/web, but “quit and reopen the app” is the native iOS client.

This is a major bug on the iOS thread-open path, not just a missing Compacting label.

What already exists

Mobile already shows a Compacting… pill once the thread is ready and compaction came from an explicit /compact (use-thread-composer-state.ts → ThreadDetailScreen → floating-working-control.tsx). Web/desktop use the same /compact heuristic (ChatView.tsx).

Claude auto-compact never writes that user message, so it still looks like a normal running turn. That indicator gap is #10962. It does not explain a process-wide lock.

Likely cause

First paint / subscribe of a live compacting thread is taking down or stalling the JS runtime:

1. Hermes fatal during feed/activity presentation — same class as #11233 (open thread → app dies).
2. JS-thread stall on subscribeThread + snapshot apply (packages/client-runtime/src/state/threads.ts) plus a full buildThreadFeed rebuild (use-thread-composer-state.ts) while compaction is rewriting the thread.
3. Stuck Opening thread… (ThreadRouteScreen.tsx) if detail never leaves synchronizing, with a frozen JS thread so native back also fails.

Server compaction queues later sends (#11107); it should not block subscribe.

Related

• #11233 — Hermes crash on thread open
• #10962 — Compacting label for auto-compact
• #9293 — /compact + Compacting UI
• #10486, #11687 — iOS open / catch-up performance

Not a duplicate.

Next step

Repro on RN iOS: /compact (and Claude auto-compact), leave the thread, open it from the list. Check the device console for a Hermes fatal; if none, profile subscribe/apply/feed rebuild. Confirm whether Home/back still works after the failed open.

If you have them: App Store vs TestFlight build, provider (Claude/Codex/…), /compact vs auto-compact, and a screenshot or console log. Not required to start.