fix(opencode): finish prompt loop by parent link

[miaojixuezhang]

Issue for this PR

Closes #40098

Type of change

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

What does this PR do?

A finished assistant turn is linked to its user message by parentID. Comparing their IDs assumes the client and server clocks agree; when a client clock is ahead, the prompt loop can run the completed turn again. This uses the parent link instead and adds a regression test with deliberately reversed ID order.

How did you verify your code works?

• Regression test times out before the fix and passes after it.
• bun test test/session/prompt.test.ts — 57 pass, 1 skip.
• bun typecheck from packages/opencode.
• Prettier check on both changed files.

Screenshots / recordings

Not applicable; this is a prompt-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:

Based on my search results, I found one highly relevant related PR:

Potential Related PR:

• PR fix(session): end the turn loop by reply parent, not message ID order #38387: fix(session): end the turn loop by reply parent, not message ID order
  • This appears to address the exact same issue: using parent links instead of message ID comparison to determine loop completion, which prevents duplicate execution when clocks are misaligned.

This PR seems directly related to the current PR #40099, as both fix the prompt loop logic by switching from ID-based comparison to parent-link-based logic. However, since PR #38387 already exists, you may want to verify if:

1. This is a regression that needs fixing again, or
2. The fix from fix(session): end the turn loop by reply parent, not message ID order #38387 needs adjustment/expansion