[harness] compaction-loss: Compaction replaced the lead's transcript with a 4 KB stub;

Context. Solo-operator project using Claude Code (desktop app, Windows 11) with a lead session on Claude Fable 5.1 orchestrating Opus 5.5 / Sonnet subagents (worktree-isolated), a JSON task store, PreToolUse/SubagentStop hooks and a harvest-train commit flow. This finding was measured on or before 2026-09-22 and filed on 2026-09-28 at the operator's request; numbers are from tool output. No secrets, identities or private paths.

Class / model / severity. compaction-loss / harness + model / HIGH

Finding. Compaction replaced the lead's transcript with a 4 KB stub; a 16-round reasoning census stated its write list at round 16 and none of it was written before the cut; only the summary survived.

Evidence (measured). Ledger LESSONS RECORD class I; the session jsonl is 3.8 KB post-compaction; subagent transcripts persist, the lead's does not.

Minimal reproduction. Run 15 reasoning-tool rounds then trigger compaction; check what survives.

Ask. Persist reasoning-tool outputs to disk as they happen; a census writes as it goes; hand the pre-compact hook the transcript path.