[Bug]: Resuming a usage-limited thread after switching models continues on the previous model #17164

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. Start a thread and let it stop on a provider usage limit. The composer shows the resume (send) button.
2. In the model picker, switch to another model or provider account that isn't limited.
3. Leave the composer empty and press the resume/send button.

Expected behavior

The thread continues with the model that is now selected in the picker.

Actual behavior

A "Continue where you left off." message is sent, but the new run uses the previous, still-limited model. The picker's choice is ignored, so the run hits the usage limit again. To actually switch models, you have to type and send a new message yourself.

onResume in apps/web/src/components/ChatView.tsx dispatches message.dispatch with manualContinuationOfRunId but no modelSelection. The server then falls back to projection.thread.modelSelection, which is the old model.

Impact

Major degradation or frequent failure

Version or commit

main @ 5e22256

Environment

macOS, web client on a dev server, Claude provider (Opus 5.5 → Sonnet 5.5 on another account)

Workaround

Type a new message instead of using the resume button. Sending a new message uses the picked model.