fix(session): break infinite compaction loop

[ranxianglei]

Issue for this PR

Closes #27924

Type of change

• Bug fix

What does this PR do?

The session loop in prompt.ts can enter an infinite compaction loop when compression fails to reduce the context below the token limit. The loop spins indefinitely consuming API credits without making progress.

Change in session/prompt.ts:

Add a compactionAttempts counter in the loop:

• Increment before each compaction attempt (both overflow and compact paths)
• If counter >= 2, break the loop with a log message
• Reset counter to 0 when normal processing progresses (i.e., agent/tool call path)

This is a safety guard, not a fix for underlying compaction failure. The counter is per-loop-invocation (reset on each new runLoop call), so it doesn't persist across sessions.

How did you verify your code works?

This fix has been running in our fork (based on v1.14.41) for several days without issues. The change was manually applied to the current dev branch rather than cherry-picked due to significant code divergence.

Verified that:

• Infinite compaction loop is broken after 2 attempts
• Normal compaction (when it succeeds) is unaffected
• No regressions in session flow

Checklist

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

[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]

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

Based on my search, I found several related PRs that address similar session/compaction issues:

Potentially Related PRs:

1. fix(session): compact finished overflowed turns #27730 - "fix(session): compact finished overflowed turns"

   • Addresses session overflow and compaction handling

2. fix(session): prevent double compaction after auto-compact #26484 - "fix(session): prevent double compaction after auto-compact"

   • Directly related to preventing unwanted compaction loops/repetition

3. fix(session): prevent double compaction when task already pending #26235 - "fix(session): prevent double compaction when task already pending"

   • Similar prevention pattern for compaction issues

4. feat(session): add custom compaction thresholds along with prevention of continuous compaction #10123 - "feat(session): add custom compaction thresholds along with prevention of continuous compaction"

   • Earlier feature addressing continuous compaction prevention

5. fix: enable auto-compaction for sub-agents and improve context overflow detection #25180 - "fix: enable auto-compaction for sub-agents and improve context overflow detection"

   • Related to overflow detection and compaction handling

Why they're related: These PRs all address compaction loop prevention and session overflow handling in similar ways. PRs #26484 and #26235 are particularly close since they both prevent unwanted compaction repetition, similar to your counter-based approach.

Note: PR #27919 is the current PR, so it's correctly excluded from duplicates.

[github-actions]

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