[harness] message-redelivery: Teammate messages from before a compaction were re-delivered 30-60 minutes later, twice;

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. message-redelivery / harness / MEDIUM

Finding. Teammate messages from before a compaction were re-delivered 30-60 minutes later, twice; a truncated final message required a second request.

Evidence (measured). This session 08:2xZ (seat 1's and seat 2's pre-cut messages), 09:0xZ (the reviewer's truncated table).

Minimal reproduction. Compact a lead with unread teammate messages.

Ask. Dedupe by message id; never truncate a final deliverable; make message-driven actions idempotent.