Improve compaction

[dgageot]

I had cagent review the compaction code. Here's what it says:

Scenario	Behavior	Status
Successful auto-compaction	Summary + continuation added in Compact(). Tokens reset in runtime.go. Model gets a valid user message.	OK
Failed compaction (API error)	Compact() returns early — no summary, no continuation, no token reset.	OK
Empty summary	Compact() returns early at if summary == "". Same as above.	OK
Re-compaction loop	Tokens reset to 0 after success — check does not re-trigger next iteration.	OK
User-triggered /compact	Continuation added inside Compact(), then user sends a real message — both appear after the summary, model sees both. Harmless.	OK
Double compaction (very long session)	Each compaction produces its own summary + continuation, tokens reset each time.	OK

[docker-agent]

Code Review Summary

✅ No issues found

I've completed a thorough review of the compaction improvements. The implementation looks solid:

What was reviewed:

• Session compaction logic - Correctly checks if compaction succeeded by comparing message counts before/after
• Continuation message handling - Only adds the implicit user message when compaction actually produces a summary
• Token counter reset - Properly resets counters to 0 after successful compaction to prevent immediate re-triggering
• Error handling - Gracefully handles failed compaction by not adding stray messages

Test coverage:

The PR includes comprehensive tests covering:

• ✅ Continuation message is sent after successful compaction
• ✅ Token counters are reset and don't cause compaction loops
• ✅ Failed compaction doesn't add stray messages

The logic is sound and well-tested. Great work on improving the compaction feature!

[rumpl]

I think this is actually the issue, we are putting the session summary as a system prompt, but it should be a user message https://github.com/docker/cagent/blob/main/pkg/session/session.go#L602

[dgageot]

@rumpl please take a look at fixing this right. I'm closing the PR