[feedback] blob-copy-merge: A manual harvest remedy copied branch blobs over a base main had moved past, reverting a sibling lane's landed

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. blob-copy-merge / Fable 5.1 (lead) / HIGH

Finding. A manual harvest remedy copied branch blobs over a base main had moved past, reverting a sibling lane's landed fix without any conflict.

Evidence (measured). judge-rh-r2-seat1 F1 (the re-introduced pyproject entry); board #1216 (three-way merge as L4).

Minimal reproduction. Two branches touch one file; land one by blob copy after the other merged.

Ask. Multi-agent landings are conflict-aware three-way merges by default; refuse a blob copy where main differs from the fork point.