isPhantomExecutorBinding's liveness gate (heartbeat/checkout/runAudit) is
structurally blind to ephemeral executor agents, leaving only the
age>graceMs*3 (~30 min) threshold, so any ephemeral-executor task running
longer than ~30 min was reclaimed to `todo` mid-flight and its worktree
destroyed. Add the in-process live-session veto (activeSessionRegistry path /
executingTaskLock / isTaskActive), mirroring the isWorkspaceTaskLive/sessionDead
predicate, and honor clearPhantomExecutorBinding's live-session refusal in
reclaimSelfOwnedBranchConflicts. Legitimate FN-6736 leaked-binding recovery is
preserved (empty registry / no lock / inactive task still reads as phantom).
Fusion-Task-Id: FN-7566
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
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