fix(session): stop prompt loop by assistant parent

[YOMXXX]

Issue for this PR

Closes#29478

Type of change

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

What does this PR do?

SessionPrompt.run used lastUser.id < lastAssistant.id to decide whether a finished assistant message should stop the prompt loop. Web clients can submit their own user message IDs, and those IDs can sort after the server-created assistant ID even when the assistant is the final answer for that user message.

This switches the stop condition to the actual turn relationship: lastAssistant.parentID === lastUser.id. The loop now exits when the latest finished assistant answers the latest user message, independent of client/server ID ordering.

The regression test seeds a Web-style user ID that sorts after its assistant ID and verifies the loop returns that finished assistant without making another LLM request.

How did you verify your code works?

• PATH="$HOME/.bun/bin:$PATH" bun test test/session/prompt.test.ts -t "loop exits when a client user id sorts after its assistant id"
  • Red before the fix: expected the seeded assistant ID, received a new assistant ID from an extra LLM call.
  • Green after the fix: 1 pass, 0 fail.
• PATH="$HOME/.bun/bin:$PATH" bun test test/session/prompt.test.ts
  • 55 pass, 0 fail.
• PATH="$HOME/.bun/bin:$PATH" bun typecheck from packages/opencode.
• PATH="$HOME/.bun/bin:$PATH" bun x prettier --check src/session/prompt.ts test/session/prompt.test.ts.
• git diff --check.
• PATH="$HOME/.bun/bin:$PATH" .husky/pre-push currently fails in unrelated @opencode-ai/console-support typecheck because local dependencies/generated console-core modules are missing (@solidjs/*, solid-js/jsx-runtime, vite, @opencode-ai/console-core/*). The touched opencode package typecheck completed separately and passed.

Screenshots / recordings

N/A - backend/session loop fix.

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 several related PRs that address similar prompt loop exit condition issues:

Potential Duplicates/Related PRs:

1. PR fix(session): use parent link for prompt loop exit #29038 - fix(session): use parent link for prompt loop exit

   • fix(session): use parent link for prompt loop exit #29038
   • Very similar fix targeting the same issue in the prompt loop exit condition

2. PR fix(session): order prompt loop by message creation #29035 - fix(session): order prompt loop by message creation

   • fix(session): order prompt loop by message creation #29035
   • Related to prompt loop ordering logic

3. PR fix(session): use server timestamps instead of IDs in runLoop exit condition #28637 - fix(session): use server timestamps instead of IDs in runLoop exit condition

   • fix(session): use server timestamps instead of IDs in runLoop exit condition #28637
   • Also addresses runLoop exit condition issues with ID/timestamp ordering

Note: PR #29038 appears to be the closest duplicate, as it directly addresses using the parent link for prompt loop exit—which is exactly what PR #29480 implements. You may want to verify which PR was created first and whether they're addressing the same underlying issue (#29478).