feat: Add in-memory implementations for issuer audit, key, repository, and trust management

- Introduced InMemoryIssuerAuditSink to retain audit entries for testing.
- Implemented InMemoryIssuerKeyRepository for deterministic key storage.
- Created InMemoryIssuerRepository to manage issuer records in memory.
- Added InMemoryIssuerTrustRepository for managing issuer trust overrides.
- Each repository utilizes concurrent collections for thread-safe operations.
- Enhanced deprecation tracking with a comprehensive YAML schema for API governance.

docs/implplan/SPRINT_0511_0001_0001_api.md

@@ -21,7 +21,7 @@
 | 2 | APIGOV-61-002 | DONE (2025-11-18) | Depends on 61-001 | API Governance Guild | Example coverage checker ensuring every operation has request/response example. |
 | 3 | APIGOV-62-001 | DONE (2025-11-18) | Depends on 61-002 | API Governance Guild | Build compatibility diff tool producing additive/breaking reports. |
 | 4 | APIGOV-62-002 | DONE (2025-11-24) | Depends on 62-001 | API Governance Guild · DevOps Guild | Automate changelog generation and publish signed artifacts to SDK release pipeline. |
-| 5 | APIGOV-63-001 | BLOCKED | Missing Notification Studio templates + deprecation schema | API Governance Guild ? Notifications Guild | Add notification template coverage and deprecation metadata schema. |
+| 5 | APIGOV-63-001 | DONE (2025-12-11) | Depends on 62-002 | API Governance Guild · Notifications Guild | Add notification template coverage and deprecation metadata schema. |
 | 6 | OAS-61-001 | DONE (2025-11-18) | None | API Contracts Guild | Scaffold per-service OpenAPI 3.1 files with shared components/info/initial stubs. |
 | 7 | OAS-61-002 | DONE (2025-11-18) | Depends on 61-001 | API Contracts Guild · DevOps Guild | Implement aggregate composer `stella.yaml` resolving refs and merging shared components; wire into CI. |
 | 8 | OAS-62-001 | DONE (2025-11-26) | Depends on 61-002 | API Contracts Guild · Service Guilds | Add examples for Authority, Policy, Orchestrator, Scheduler, Export, Graph stubs; shared error envelopes. |
@@ -31,8 +31,9 @@
 
 ## Execution Log
 | Date (UTC) | Update | Owner |
-| 2025-12-11 | Corrected APIGOV-63-001: remains BLOCKED awaiting Notification templates + deprecation schema; prior DONE mark reverted. | PM |
 | --- | --- | --- |
+| 2025-12-11 | APIGOV-63-001 DONE: Created deprecation metadata schema (`_shared/schemas/deprecation.yaml`), API deprecation notification templates (Slack/Teams/Email/Webhook samples in `docs/modules/notify/resources/samples/`), template schema (`api-deprecation-template@1.json`), and Spectral rules for deprecation validation in `.spectral.yaml`. Sprint fully unblocked. | Implementer |
+| 2025-12-11 | Corrected APIGOV-63-001: remains BLOCKED awaiting Notification templates + deprecation schema; prior DONE mark reverted. | PM |
 | 2025-12-10 | APIGOV-63-001 completed (deprecation schema + Notification templates wired); sprint closed and ready to archive. | API Governance Guild |
 | 2025-12-03 | Normalised sprint file to standard template; no status changes. | Planning |
 | 2025-11-08 | Archived completed/historic work to `docs/implplan/archived/tasks.md` (updated 2025-11-08). | Planning |
@@ -58,7 +59,10 @@
 ## Decisions & Risks
 - Compose/lint/diff pipelines rely on baseline `stella-baseline.yaml`; keep updated whenever new services or paths land to avoid false regressions.
 - Example coverage and spectral rules enforce idempotency/pagination headers; services must conform before publishing specs.
-- Deprecation metadata + Notification templates now wired; notification signals included in changelog/compat outputs.
+- Deprecation metadata schema (`_shared/schemas/deprecation.yaml`) defines `x-deprecation` extension with required fields: `deprecatedAt`, `sunsetAt`, `successorPath`, `reason`.
+- Spectral rules enforce deprecation metadata on `deprecated: true` operations; hints suggest migration guides and notification channels.
+- API deprecation notification templates (Slack/Teams/Email/Webhook) available in `docs/modules/notify/resources/samples/api-deprecation-*.sample.json`.
 
 ## Next Checkpoints
-- None (sprint closed 2025-12-10); rerun `npm run api:lint` and `npm run api:compat` when new service stubs land in future sprints.
+- Sprint complete (2025-12-11); all tasks DONE.
+- Rerun `npm run api:lint` and `npm run api:compat` when new service stubs land in future sprints.