Fix err msg order

[LydiaCai1203]

Issue for this PR

Closes #21314

Type of change

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

What does this PR do?

This PR fixes an issue where session updates could be applied out of order, leading to incorrectly ordered messages.

The root cause was that session updates were processed concurrently, so their execution order was not guaranteed. As a result, message ordering could become inconsistent depending on timing.

This change serializes session updates to ensure they are processed in a strict sequence. By enforcing ordered execution, message order is now deterministic and consistent, avoiding race conditions without introducing significant overhead.

How did you verify your code works?

• Reproduced the issue locally by triggering multiple rapid session updates
• Observed that messages could appear out of order before the fix
• Verified that after this change, messages are consistently ordered
• Tested normal flows to ensure no regressions

Screenshots / recordings

N/A

Checklist

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

[github-actions]

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[github-actions]

Hey! Your PR title Fix err msg order doesn't follow conventional commit format.

Please update it to start with one of:

• feat: or feat(scope): new feature
• fix: or fix(scope): bug fix
• docs: or docs(scope): documentation changes
• chore: or chore(scope): maintenance tasks
• refactor: or refactor(scope): code refactoring
• test: or test(scope): adding or updating tests

Where scope is the package name (e.g., app, desktop, opencode).

See CONTRIBUTING.md for details.

[github-actions]

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

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

Related PR:

• #17149: fix(web): order session messages by creation time - This PR also addresses message ordering in sessions, which is closely related to the current PR's focus on ensuring session updates are processed in order to maintain consistent message ordering.

This PR (21473) appears to fix the underlying root cause (serializing session updates to prevent race conditions), while PR #17149 specifically addresses ordering messages by creation time on the web side. They are complementary fixes for message ordering issues.

No other duplicate PRs found that directly address the same issue.

[github-actions]

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