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

[YLRong]

Issue for this PR

Closes #14935

Type of change

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

What does this PR do?

Fixes duplicate assistant responses caused by clock skew between client and server systems.

Problem: When client and server have different system times (clock skew), the prompt loop's exit condition lastUser.id < lastAssistant.id fails because message IDs are timestamp-based. This causes the loop to continue and generate a second assistant response for the same user message.

Solution: Replace timestamp-based comparison with explicit parentID relationship check. The assistant message's parentID field already stores the ID of the user message it responds to, making this a more reliable indicator than timestamp comparison.

The change adds:

• Primary check using lastAssistant.parentID === lastUser.id
• Fallback to timestamp comparison for backward compatibility with messages that may not have parentID set

This fix is needed because the timestamp-based approach assumes client and server clocks are synchronized, which is not always true in real-world deployments.

How did you verify your code works?

Tested with OpenChamber 1.9.3 + OpenCode 1.3.17:

1. Reproduced the issue by setting server time 10 seconds faster than client
2. Confirmed duplicate assistant responses before the fix
3. Verified single response after the fix
4. Tested with server time 10 seconds slower - works correctly

The fix uses existing fields (parentID) that are already populated correctly, so no migration is needed.

Screenshots / recordings

N/A - This is a backend logic 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 potentially related PRs that address similar issues:

1. fix: use parentID matching instead of ID ordering for prompt loop exit and message rendering #14307 - "fix: use parentID matching instead of ID ordering for prompt loop exit and message rendering"

   • Directly related: This PR also addresses the loop exit condition using parentID matching, which is the same core fix as PR fix(session): use parentID instead of timestamp for loop exit condition #21334.

2. fix: server-generated message IDs to prevent client/server clock skew #11869 - "fix: server-generated message IDs to prevent client/server clock skew"

   • Related: Addresses clock skew issues between client and server by using server-generated message IDs, which is the underlying problem that PR fix(session): use parentID instead of timestamp for loop exit condition #21334 is trying to solve.

These PRs appear to be addressing the same or very similar issues with the prompt loop exit condition and clock skew. You should verify if PR #14307 is a previous attempt at the same fix or if there's overlap in scope.