docs: an abandoned claim is invisible to its holder and blocking to everyone else

[ZacxDev]

Session close-out. Two commits: the durable lesson lands in the skill reference that owns it, and the handoff records the arc state.

🔴 The finding

While answering "is anything outstanding?" I ran claim-work --list and found cairn-oss-multi-instance-20 claimed for 5 days on work that is still open and that nobody was doing.

It survived because of an asymmetry that isn't visible from the exit codes read one at a time. The ownership token is /etc/machine-id + git rev-parse --git-dir, so the same unreleased ref answers:

• rc 12 — THIS SESSION (you already hold it) — carry on, to the clone that claimed it
• rc 10 — ALREADY CLAIMED — STOP, to the other host or any other clone

So a claim nobody is working reads as fine from exactly the machine that could clear it, and as taken from the machines it obstructs. Neither side sees the contradiction: the holder is told to carry on, the blocked session is told someone is on it, and nothing expires the ref in a way a human notices. It surfaced only because a human asked — not from any check the workflow performs.

Released; the arc now holds zero claims.

Where it landed

claude/skills/handoff/reference/shared-queue.md — the file that already owns the claim protocol — rather than only in a handoff, which gets overwritten. Adds two habits needing no --force: release your own unlanded claims at session end, and read the list before assuming an inherited queue is free.

⚠ Explicitly does not license auto-stealing. The file's existing reasoning stands — "the holder went quiet for a week" and "the holder is on a long piece of work" are the same observable, which is why --steal is a separate deliberate verb. What changes is that the holder now has a reason to look, being the one party the stale ref never warns.

Handoff

Also records the second gotcha this session produced: "is anything outstanding?" is answered by the closing-condition, not by the ranked list, and the two gave opposite answers. Ranks 4, 23 and 26 all closed and the queue read as productive; the frozen closing-condition says the arc has not arrived — phase B has not started and ranks 25/27/28 cannot advance it. A ranked list measures activity; only a frozen closing-condition measures arrival.

193,498 B of 196,608 B — 3,110 B headroom. The tool's advisory notes the next update or two will go over; claudedocs/refs/cairn-oss-multi-instance.md is the demote target.

⚠ No clawgate-task: field: resolve exited 5 with a positive control (the same endpoint answered 9 links for another session), so the board is reachable and this session genuinely has no task.