feat(j5): terminate archived participant obligations

[Jacksondr5]

Problem

Retiring an A2A participant could silently strand open exchanges, leaving the counterparty waiting without a truthful terminal fact.

Fix

• Add an idempotent lifecycle bridge for committed thread.archived and thread.deleted events: registered participants retire with complete participant.left history and their open exchanges become exchange.dropped.
• Deliver one platform-authored terminal lifecycle notice through the normal delivery pipeline; keep retired participants hidden from active membership while the ledger remains readable.
• Add ArchiveFactsService as a display-only, composable AR2 read boundary; placement is a discriminated unknown/none/known state pending ratification.
• Close the A3/A9 race with a permit-and-transaction conditional silence append, so a stale silence notice cannot follow a committed drop.
• Add migration 008_LifecycleClosure, expanding terminal exchange state while opaquely preserving A4 inbox rows across SQLite parent-table rebuilds.

Settled scope and migration contracts

• The DV5 product decision and the archive-flow settlement defer all Squadron archive surface/schema work to SC4-later; this PR intentionally adds no archive operation, HTTP/MCP surface, or Squadron schema.
• The updated A9 ticket records the Option-A migration contract: preserve every A4 inbox field byte-for-byte in one transaction and flag future parent rebuilds for a shared helper.
• Migration 008 follows merged 006/007. SQ1 owns 009 in feat(j5): add Squadron creation surface #20; its interim manifest is intentionally non-contiguous until this PR merges. Whichever PR lands second will rebase and verify the full ordered 001–009 manifest.

Verification

• Independent exact-head review: READY at 8861c66386fe5b4cf2a4b13bc719d3fa8df3b860; targeted domain/migration/runtime suites, mutation controls, typecheck, and lint passed.
• Final isolated Codex Luna E2E: real archive produced participant.left -> exchange.dropped -> one delivered lifecycle_notice; the waiter acknowledged “I won’t retry or replace the retired participant”; an archived-sender reply failed closed with A2ASenderRetiredError and appended zero events. Evidence: Traycer artifact a9-luna-e2e (worktree-local state; exact-PID teardown).

Coverage limits

AR2 is service-complete but has no route or MCP registration until the human archive-dialog surface is ratified. Squadron archive, warn/confirm UI, and re-entry semantics remain deliberately out of scope.

Built with Codex / GPT-5.6.

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[Jacksondr5]

Final lifecycle E2E attestation

At exact head 8861c66386fe5b4cf2a4b13bc719d3fa8df3b860, an isolated real Codex Luna run drove thread.archive for a registered receiver. The production pipeline persisted complete-payload participant.left, exchange.dropped (receiver-retired, replyRequired=false, retryAllowed=false, replacementRequired=false), one lifecycle_notice terminal message.sent, and a delivered receipt. The waiter received the terminal notice and replied: “Understood. I won’t retry or replace the retired participant.”

Negative control: the archived participant’s reply was rejected with A2ASenderRetiredError, appended zero ledger events, and terminal-notice count stayed one. Server state was worktree-local and shut down via captured PID only. Full evidence is retained in Traycer artifact a9-luna-e2e.

Posted by an AI agent on Jackson's behalf.