Claims are branches on the shared remote; nothing kept on one computer is the register; claim text is data

Context

On 2026-10-03 a second person began working on abcd from their own computer, the repository was public, and a hosted cloud session with its own clone was admitted as one more participant. Everything abcd used to keep agents apart lived on one computer: The shared run's exclusive-create lease under the machine-scoped run store (itd-2609221656373558), the sibling-worktree listing, and notes the sessions left each other. None of it reaches the second person or the cloud session, so their agents and ours could each start the same item, and the first anyone would hear of it is the collision at merge (iss-2609020716570699).

The product thinker ruled the same day that coordination must be visible to every participant, that a claim is a marker on the shared remote which abcd lists, and that reserving one item is built first (itd-2609091034175565, decisions 1 to 4; itd-2609150819440345, decision 4). The state of the art and the run lessons behind those rulings are in 2026-10-03-multi-agent-coordination-sota-and-run-lessons.md.

Two adversarial reviews of the design followed, and their evidence fixed the transport rather than leaving it to preference:

• A hosted cloud session's git proxy rejects branch deletions and pushes of anything other than a branch; a probe on 2026-10-03 got HTTP 403 on a ref under refs/abcd/ while branch pushes succeeded. A ref outside refs/heads/ cannot include the cloud session.
• abcd's hazard registry refuses every --force-with-lease push, and the proxy refuses deletions, so neither a lease flag nor a deletion is available. A plain push already compares and swaps: a parentless commit over an existing branch is rejected as non-fast-forward, and two children of one parent admit exactly one.
• The committed pre-push hook demands a preflight receipt for every new commit, so it refuses a claim push today; an exemption by branch name alone would let code past the receipt gate.
• A claim's text is written by whoever has write access and is read by agents, and the 2026 incidents in the state of the art are agents following instructions planted in exactly such channels.
• Anyone with write access can push to or delete any branch outside the default branch, which is all this repository's rulesets protect.

Brief invariant 7 already holds that implicit operations never touch the network (adr-38).

Decision

We will hold a claim on a record as a branch on the shared remote, refs/heads/abcd-reserved/<record-id> (a person reads it as a reservation; the record and the code call it a claim), and nowhere else:

1. The branch is the transport, and the only one. A claim branch is a chain of commits with the empty tree, which nobody merges and abcd lists. It is a branch because a hosted cloud session can push nothing else. No hidden-ref backend sits beside it. Every claim act is a plain fast-forward push: a parentless create, a renewal or takeover as a child, and a release as a tombstone child; abcd uses no lease flag and deletes no claim branch.
2. Nothing kept on one computer is the source of truth for who holds what. The local tier, the machine-scoped run store, a desktop note and same-account messaging may speed up notice; the claim branch on the remote decides. A claim that cannot reach the remote is refused loudly and is never recorded locally as if it were shared.
3. Claim text is data. A claim is parsed by its known trailer keys and rendered as quoted values; an unknown key is ignored, a malformed or oversized claim is reported as unreadable, and no part of a claim is ever handed to an agent as instructions. Footprint paths never reach a shell or a refspec, and the branch name is built only from a valid record id.
4. Claims are advisory among trusted writers. A claim refuses nothing at the forge: Any writer can push to it or delete it. abcd's verbs honour it, expiry is judged by the reader, and the land stage re-checks it before arming a merge.
5. The pre-push exemption covers empty-tree claim commits only. The repository's pre-push hook passes an update to refs/heads/abcd-reserved/* without a preflight receipt only when every commit in the pushed range has the empty tree; every other push, and every non-fast-forward push, is gated as before.
6. Every network act is an explicit verb. abcd reserve and its release, abcd build, abcd drain and abcd peers push or fetch reservations because that is their documented meaning, and implement step reads and writes the run's reservation because its documented meaning is extended to say so; a branch push is not remote configuration. A reservation stops counting once its record is terminal on the default branch, so no step after the merge is needed. Every render, gate, hook and session start reads the claims only as last fetched, from disk.

Alternatives Considered

• A ref outside refs/heads/ (refs/abcd/claims/<record-id>), hidden from the forge's website. The product thinker's first choice; rejected on the cloud probe, because the cloud session could neither claim nor release.
• Both a hidden ref and a branch. Rejected: Two backends are two bug surfaces, and the hidden ref buys nothing a cloud session can use.
• A lease kept on one machine (the run store, the shared .git, or the host's session registry). Rejected by the visibility ruling: The second person never sees it.
• A claimed_by stamp on the record, pushed through a pull request. Rejected: An older reader skips a record with an unknown key, so it needed a two-release migration, and each claim paid a merge-queue pass of fifteen to sixteen minutes.
• A forge claim (an issue assignment or a draft pull request). Kept for outside contributors, who cannot push a branch (itd-2610031259176838); it needs a forge client and token that a cloud session lacks.

Consequences

• A claim costs one push of seconds, with no pull request, queue pass or workflow run, since every push trigger filters on the default branch or release tags.
• Claim branches show in the forge's branch list and may raise a compare-and-pull-request banner; every claimed record leaves a tombstoned branch, so the clean-up sweep of itd-118 is owed before the forge's 5,000-branch limit matters.
• A malicious or careless writer can delete or overwrite a claim; the design accepts this among trusted writers and does not defend against it.
• Brief invariant 7's documented-meaning entries must name the reservation verbs and implement step's reservation write, and invariant 10 gains one clause saying a git branch push is not remote configuration (the technical facilitator's ruling of 2026-10-03, itd-2609091034175565 decision 12); both land in the change that builds the reservation, not before.
• The shipped implement claim and the remote claim judge liveness through one function, so the lease arithmetic has one home.