Plan→Compact→Re-Plan infinite loop in Copilot CLI (217 cycles, zero execution)

[Akhi-microsoft]

👋 Hey Copilot CLI team — filing a high-severity bug. John (Agency team) routed me here from aka.ms/copilotcli/support since I don't have access to the form.

What happened

Coding session in copilot (via agency copilot wrapper). At ~75% context, the agent compacted, re-read the summary, and resumed PLANNING instead of executing. Repeated 217 times before I killed it. Zero file edits. Hours of compute and quota gone.

Root cause (hypothesis)

Compaction preserves the plan as the most salient signal post-compact. The agent treats "we have a plan" as a fresh prompt to plan against, instead of as decided work to execute. Structural, not prompt-specific.

Repro

1. copilot (or agency copilot)
2. Moderately complex prompt (feature across files A/B/C with tests)
3. No AGENTS.md guardrails
4. Let session run past auto-compact threshold
5. Post-compact: agent plans again instead of editing files. Loops.

Appears deterministic.

Impact

• Hundreds of model calls, zero output
• Full session lost, manual recovery required
• Undermines trust in long-running autonomous tasks
• Likely under-reported (users blame themselves before the tool)

Proposed fixes (priority order)

1. Compaction summarizer: label plans as "DECIDED — do not re-plan"
2. Default post-compact rule: "Resume from next file edit, do not re-validate the plan" (ref: https://github.com/Dicklesworthstone/post_compact_reminder)
3. Add --mode execute session flag biased against planning preambles
4. Loop detector: N consecutive turns with zero file edits → halt (default N=3)
5. Better /compact defaults: drop planning history
6. Telemetry signal for "planning loop suspected"

Workarounds I'm using

AGENTS.md "no re-plan after compact" rule + post-compact reminder hook + manual /compact at ~60% + HANDOFF.md as ground-truth state file. These work but shouldn't be required of every user.

Environment

• Copilot CLI: 1.0.41
• Node: v22.22.2
• OS: Windows

Happy to share session logs and join a triage call.

— Akhi Shukla, Senior PM, IC3 / UED, Prague