Entire

Snapshot a stopping background subagent before completing its record: while the record is live the worktree is busy, so a prompt racing the stop cannot take its unsnapshotted edits for the user's.
A session-store read failure is not idle: the prompt's user diff is marked incomplete instead of computed.
A live subagent whose owner liveness is unknown counts only while its session interacted within StuckActiveThreshold, the Owner contract's fallback, instead of forever.
Sessions without a worktree path are skipped, as session matching does.
A snapshot of a shared worktree leaves files other live sessions there have touched out of this session's FilesTouched.
WriteEphemeralOptions docs describe full-worktree snapshots.

Co-Authored-By: Claude Opus 5.5 noreply@anthropic.com Entire-Checkpoint: 01M43EGMF0AGR6JK92Z2DFFH4H

Close the busy-window review gaps on #2651