fix(session): avoid stuck sessions from empty responses and compaction races

[askforoneZY]

Issue for this PR

Closes #30411

Related: #3189, #2609, #5449, #2987, #4845, #6286, #6071, #5970, #5178, #6446

Type of change

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

What does this PR do?

Fixes session stalls caused by empty responses and compaction races.

This PR adds per-session compaction single-flight behavior so manual /compact, HTTP summarize, auto-overflow compaction, and processor-triggered compact requests join or reuse existing work instead of creating duplicate compaction markers.

It also delays prompt/command message append while compaction is active or pending, pauses normal model/tool continuation during compaction, and makes empty/unknown responses near context pressure compact or fail deterministically instead of silently doing nothing.

How did you verify your code works?

• Added focused tests for duplicate compaction marker prevention.
• Added HTTP summarize dedupe coverage.
• Added prompt/command wait-before-append coverage.
• Added manual compact preemption and resume-once coverage.
• Added ownerless active compaction no-deadlock coverage.
• Added empty unknown response near context limit coverage.
• bun turbo typecheck passed across 21 packages in the pre-push hook.

Screenshots / recordings

Not a UI change.

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, I found one potentially related PR:

PR #29888 - fix(app): add open folder button to V2 desktop session header

• fix(app): add open folder button to V2 desktop session header #29888
• This PR appears to be directly related to the current PR fix(session): avoid stuck sessions from empty responses and compaction races #30304, as both address open folder functionality in the V2 desktop session header. They may be addressing the same issue or this could be a predecessor/related attempt at the same feature.

[github-actions]

Thanks for your contribution!

This PR doesn't have a linked issue. All PRs must reference an existing issue.

Please:

1. Open an issue describing the bug/feature (if one doesn't exist)
2. Add Fixes #<number> or Closes #<number> to this PR description

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[github-actions]

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[github-actions]

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