fix: prevent web ui session loop by removing client-side message id g…

[aadilshaikh123]

Issue for this PR

Closes #17012

Type of change

• Bug fix
• New feature
• Refactor / code improvement
• Documentation

What does this PR do?

The Web UI was generating message IDs client-side and including them in the API request. This breaks the session loop's monotonic ID ordering assumption, causing the loop to not exit properly and create multiple assistant messages for a single user message.

The fix removes client-side message ID generation and lets the server handle it exclusively, maintaining proper ID ordering and preventing the session loop from misfiring.

For the optimistic UI, we still generate a temporary ID locally that gets replaced when the server returns the actual message.

How did you verify your code works?

I traced the code flow:

1. Reviewed the session loop logic in packages/opencode/src/session/prompt.ts
2. Confirmed that monotonic ID ordering is required for the loop exit condition (lastUser.id < lastAssistant.id)
3. Verified that client-side ID generation was breaking this ordering
4. Confirmed the fix maintains server-side ID generation while keeping optimistic UI working with temporary IDs

Screenshots / recordings

Not applicable - backend fix without UI changes

Checklist

• I have tested my changes locally
• I have not included unrelated changes in this PR

[github-actions]

The following comment was made by an LLM, it may be inaccurate:

I found a related PR that addresses a similar issue:

Related PR:

• PR fix(session): use parentID instead of timestamp for loop exit condition #21334: fix(session): use parentID instead of timestamp for loop exit condition

  • fix(session): use parentID instead of timestamp for loop exit condition #21334

  This PR is related as it also addresses the session loop exit condition logic, which is the core issue that PR fix: prevent web ui session loop by removing client-side message id g… #21361 is fixing. PR fix: prevent web ui session loop by removing client-side message id g… #21361 prevents incorrect client-side message ID generation that breaks the monotonic ID ordering assumption, while PR fix(session): use parentID instead of timestamp for loop exit condition #21334 seems to address the loop exit condition directly.

Both PRs touch the same core problem (session loop and message ID ordering), so they may need coordination to avoid conflicts.