[BUG] Cowork: final assistant message invisible until user sends next prompt

Bug

When Claude finishes a multi-step tool-call sequence in Cowork mode, the final assistant text message is generated but not rendered in the UI. The spinner stops, the todo list shows all tasks complete, but the response text is invisible. It only appears after the user types a new message and presses Enter.

Environment

• Platform: macOS (Mac Mini, Apple Silicon)
• Mode: Cowork
• Reproducibility: Consistent — happens reliably after long tool-call sequences (5+ tool calls)

Steps to Reproduce

1. Start a Cowork session with a mounted folder
2. Ask Claude to perform a multi-step task (e.g., "fix all failing tests" involving 10+ tool calls via Desktop Commander)
3. Wait for Claude to finish — spinner stops, todo list shows complete
4. Observe: no text response visible
5. Type anything and press Enter
6. Claude's completed response from step 3 now appears

Expected Behavior

The final assistant message should render immediately when generation completes, without requiring a new user input event to trigger the UI flush.

Actual Behavior

The assistant message is buffered/held and only displayed after the next user interaction (any keypress + Enter). The message content is correct when it does appear — it's purely a rendering timing issue.

Notes

• The todo list widget updates in real-time during the task — only the final text message is affected
• This appears to be a frontend message rendering lifecycle issue, not a backend/generation problem
• Observed consistently across multiple sessions over several days