Plan→Compact→Re-Plan infinite loop after auto-compaction

[Akhi-microsoft]

Summary

After auto-compaction triggers mid-session, the agent re-reads the compaction summary and resumes planning instead of executing. This creates a self-reinforcing loop: plan → context fills → compact → re-read plan → plan again → repeat.

In one session I observed 217 plan→compact→re-plan cycles before killing it. Zero file edits across hundreds of turns.

Repro

Start a non-trivial coding task with copilot (Copilot CLI). Let auto-compaction fire mid-task. Observe that after compaction the agent re-summarizes its own plan, validates it, and repeats — instead of resuming from the next concrete file edit.

Root Cause Hypothesis

Compaction preserves the plan as the most salient signal in the new context window. Post-compact, the agent treats ""we have a plan"" as a fresh prompt to plan against, rather than as decided work to execute. With no execution-bias instruction surviving compaction, the loop is structural — not prompt-specific.

Expected Behavior

After compaction, the agent resumes from the next concrete file edit. Plans already produced are treated as decided, not as a fresh prompt to re-plan against.

Actual Behavior

Agent re-summarizes its own plan, validates it, and repeats. No file edits across hundreds of turns.

Impact

• Quota / cost: hours of compute, hundreds of model calls, zero output
• Productivity: full session lost, manual recovery required
• Trust: undermines confidence in long-running autonomous tasks
• Likely under-reported: users blame themselves before blaming the tool

Proposed Fixes (priority order)

1. Compaction summarizer: label plans as ""DECIDED — do not re-plan"" and surface ""next concrete action"" as the primary continuation signal.
2. Inject a default post-compact rule: ""Resume from the next file edit. Do not re-validate the plan."" (Reference: https://github.com/Dicklesworthstone/post_compact_reminder)
3. Add an --mode execute session flag that biases hard against planning preambles.
4. Loop detector: N consecutive turns with zero file edits → halt and prompt user. Suggested default N=3.
5. Improve /compact defaults: drop planning history, keep only files modified, current error state, and next concrete action.
6. Telemetry signal for ""planning loop suspected"" to quantify real-world frequency.

Current Workarounds (should not be required)

• AGENTS.md with explicit ""no re-plan after compact"" rule
• Post-compact reminder hook (manual third-party install)
• Manual /compact at ~60% with explicit preservation instructions
• HANDOFF.md as ground-truth state file

Reporter

Akhi Shukla — Senior PM, IC3 / UED, Prague
Manager: Bryan Castro | Skip: Nils Dussart
Happy to share session logs and join a triage call.