ticket-create: A2A claim sweep as the last step before create_issue

Context

The fix lane for tonight's dup-test. Operator @tobiu broadcast a singular "one (not all!)" task → 4 agents raced → 3 dup tickets (#12851 canonical, #12852/#12853 closed) despite every agent running the mandatory ticket-create §1a GitHub dup-sweep AND two broadcasting [lane-claim]. Lead @neo-fable handed me this substrate-fix lane with the full empirical record; this ticket encodes the operator-calibrated immediate fix (the zero-infra discipline layer). The durable tool-side backstop is a separate higher-blast lane — see Related.

The Problem

ticket-create-workflow.md §1a mandates a live GitHub dup-sweep "before any create_issue call." Two structural gaps:

1. Wrong substrate during the race window. Empirically (fable's record): for the first ~3 min of a thundering herd, the dups exist only as A2A [lane-claim]s, not GitHub tickets. fable swept GitHub at 18:35Z, filed #12851 ~18:40Z — but both competing claims (18:37:48Z vega, 18:38:32Z claude) were already in the inbox, invisible to a GitHub sweep. §1a checks GitHub state — the wrong substrate for in-flight claims.
2. Sweep runs too early (TOCTOU). Agents run §1a at the START of the create flow, then spend minutes drafting the Fat Ticket; by create_issue time the sweep is stale (mine was ~3 min stale; #12851/#12852 existed by the time I filed #12853).

The empirical winner: @neo-opus-ada used a two-phase [lane-intent] → re-check → execute and filed 0. The two-phase re-check is the mechanism that works.

The Architectural Reality

• .agents/skills/ticket-create/references/ticket-create-workflow.md §1a (Content Sweep / Live freshness sweep) — currently a single GitHub gh issue list sweep.
• A2A claims live in the Memory Core mailbox, queryable via list_messages ([lane-claim]/[lane-intent]).
• Operator calibration (direct, relayed by @neo-fable): "use list_messages as the last step again before creating the ticket — if a turn takes 5-10m and we only check first, we're still stale for minutes. Mostly an issue at session start (team starts at the same time)."
• Skill-doc (references/) amendment only — the ticket-create/SKILL.md router stays thin (Progressive Disclosure / ADR 0008 preserved). No new .mjs.

The Fix

Amend §1a Gate 0:

1. Add an A2A claim sweep as the sibling of the GitHub live-sweep: list_messages filtered for recent [lane-claim]/[lane-intent] on the same scope. GitHub sweep catches FILED dups; A2A sweep catches IN-FLIGHT dups. Same gate slot, two substrates.
2. Reposition both sweeps as the LAST action immediately before create_issue (not turn-start / pre-authoring). The turn-start mailbox check stays for general coordination but is not the dup gate.
3. Deterministic tiebreak: when a competing claim is found, first-claim-timestamp-wins — the later claimant stands down (or closes its dup), no lead mediation needed. Makes simultaneous filings self-healing.
4. Companion discipline: never wakeSuppress a contested-lane resolution (the "do-not-re-file" signal must wake, or it reaches nobody — fable's 18:41Z miss tonight).

Decision Record impact

none — refines the ticket-create process substrate; no ADR governs §1a.

Acceptance Criteria

• §1a adds an A2A claim sweep (list_messages for [lane-claim]/[lane-intent] on-scope) as a sibling to the GitHub live-sweep.
• Both sweeps mandated as the LAST step immediately before create_issue (explicit "just-in-time, not turn-start" language).
• First-claim-timestamp-wins tiebreak codified (later claimant stands down/closes).
• Companion: contested-lane resolutions must NOT be wakeSuppressed.
• Change lands in references/ticket-create-workflow.md only; SKILL.md router unchanged.
• Substrate Accretion Defense: net loaded-bytes accounted; retirement trigger = if/when the sink-side create_issue semantic dedup gate ships (the durable backstop), this discipline compresses to a trigger note.

Out of Scope

• The durable sink-side semantic dedup gate on the create_issue MCP tool (requireNoSimilarOpen + acknowledgedDuplicate, mirroring manage_issue_assignees) — higher-blast tool change, separate Ideation lane (Related). This ticket is the zero-infra discipline layer.
• Generalizing to create_discussion (same hole likely exists) — noted for the Ideation lane.

Avoided Traps

• "Just re-run the GitHub sweep before create." Half-right: it catches later-mover dups (already-filed tickets) but MISSES the first ~3 min when dups are A2A-claims-only. The A2A sweep is the missing half.
• Relying on broadcast [lane-claim] for mutual exclusion. Broadcasts deliver post-turn → concurrent responders are mutually blind. Discipline at the create-call gate + the deterministic tiebreak is what converges.

Related

• #12851 — the ticket whose 4-way race is this lane's empirical anchor.
• Ideation (drafted, auto-mode-gated): sink-side semantic dedup gate on create_issue — the durable tool-side backstop A; this ticket is the discipline layer C′.
• #11536/#11537 — the lane-claim / pre-write coordination substrate this extends.

Handoff Retrieval Hints

• query_raw_memories: "ticket-create A2A claim sweep last step before create_issue first-claim-wins"
• Empirical anchor: 2026-06-10 4-way sunset-ticket race (@neo-fable's data-handoff record).

Filed by @neo-opus-grace (Claude Opus 4.8); lane handed off by @neo-fable; operator-calibrated by @tobiu.