fix(queue): contain mixed-version retry promotion conflicts

[Joncallim]

Source Issue

Issue: #179

Summary

• distinguish genuine retry-promotion ownership contention from fatal receipt-integrity failures with a fixed typed error
• contain only that typed conflict at the task, approval, and answers promotion boundaries while preserving fatal handling for Redis, parse, integrity, and capacity errors
• prove historical v2-first and upgraded-first ordering, legacy-row quiescence, strict receipt authority, and non-disclosing loop continuation

Validation

• npx vitest run __tests__/core-diagnostic-output-closure.test.ts --config vitest.config.ts — 21/21
• disposable Redis 8 proof at a dedicated nonzero empty database — 3/3 with existing multiplicity, recovery, and shutdown markers
• npm test -- --maxWorkers=1 — 1,688 passed; environment-gated integration files remained skipped by the ordinary unit command
• exact three timeout cases from the first concurrent full-suite run — 213/213 in isolated serial retry
• assigned-file ESLint — pass
• npx tsc --noEmit --pretty false — pass
• npm run build — pass
• git diff --check — pass
• mutation checks rejected fatal typed conflicts, swallowed generic errors, fabricated stale success, and restored unbounded ready-list scanning

Documentation gate\n\nCompleted in docs/operator-guide.md at 14499270ba03c2b382bb9ad38aada001e54db871.\n\n- Operators must assume legacy retry entries exist, stop and drain every v2 worker, verify no v2 process or replica remains, and only then start current workers.\n- Raw Redis queue members must not be dumped or logged. An accidental v2 canonical winner produces only the fixed nonfatal mixed_version_retry_promotion category; it is not current-worker success and fabricates no receipt.\n- The compatibility window ends when every v2 worker stops. Opaque disposition receipts keep their normal 15-minute expiry and bounded pruning; there is no compatibility key or manual receipt cleanup.\n- Rollback stops and drains current workers first and does not restart v2 while legacy retry entries may remain.\n\nDocumentation validation: git diff --check passed. This repository has no configured Markdown formatter or documentation linter.

Scope\n\nThe implementation remains limited to the two queue/runtime files and their two focused test files. This follow-up adds only docs/operator-guide.md. No workflow, schema, migration, or Redis namespace behavior is modified.