Implement ledger metrics for observability and add tests for Ruby packages endpoints

- Added `LedgerMetrics` class to record write latency and total events for ledger operations.
- Created comprehensive tests for Ruby packages endpoints, covering scenarios for missing inventory, successful retrieval, and identifier handling.
- Introduced `TestSurfaceSecretsScope` for managing environment variables during tests.
- Developed `ProvenanceMongoExtensions` for attaching DSSE provenance and trust information to event documents.
- Implemented `EventProvenanceWriter` and `EventWriter` classes for managing event provenance in MongoDB.
- Established MongoDB indexes for efficient querying of events based on provenance and trust.
- Added models and JSON parsing logic for DSSE provenance and trust information.

docs/notifications/overview.md

@@ -21,7 +21,7 @@ Notifications Studio turns raw platform events into concise, tenant-scoped alert
 |------------|--------------|----------|
 | Rules engine | Declarative matchers for event kinds, severities, namespaces, VEX context, KEV flags, and more. | [`notifications/rules.md`](rules.md) |
 | Channel catalog | Slack, Teams, Email, Webhook connectors loaded via restart-time plug-ins; metadata stored without secrets. | [`notifications/architecture.md`](architecture.md) |
-| Templates | Locale-aware, deterministic rendering via safe helpers; channel defaults plus tenant-specific overrides. | [`notifications/templates.md`](templates.md) |
+| Templates | Locale-aware, deterministic rendering via safe helpers; channel defaults plus tenant-specific overrides, including the attestation lifecycle suite (`tmpl-attest-*`). | [`notifications/templates.md`](templates.md#7-attestation--signing-lifecycle-templates-notify-attest-74-001) |
 | Digests | Coalesce bursts into periodic summaries with deterministic IDs and audit trails. | [`notifications/digests.md`](digests.md) |
 | Delivery ledger | Tracks rendered payload hashes, attempts, throttles, and outcomes for every action. | [`modules/notify/architecture.md`](../modules/notify/architecture.md#7-data-model-mongo) |
 | Ack tokens | DSSE-signed acknowledgement tokens with webhook allowlists and escalation guardrails enforced by Authority. | [`modules/notify/architecture.md`](../modules/notify/architecture.md#81-ack-tokens--escalation-workflows) |
@@ -44,7 +44,7 @@ The Notify WebService fronts worker state with REST APIs used by the UI and CLI.
 | Area | Guidance |
 |------|----------|
 | **Tenancy** | Each rule, channel, template, and delivery belongs to exactly one tenant. Cross-tenant sharing is intentionally unsupported. |
-| **Determinism** | Configuration persistence normalises strings and sorts collections. Template rendering produces identical `bodyHash` values when inputs match. |
+| **Determinism** | Configuration persistence normalises strings and sorts collections. Template rendering produces identical `bodyHash` values when inputs match; attestation events always reference the canonical `tmpl-attest-*` keys documented in the template guide. |
 | **Scaling** | Workers scale horizontally; per-tenant rule snapshots are cached and refreshed from Mongo change streams. Redis (or equivalent) guards throttles and locks. |
 | **Offline** | Offline Kits include plug-ins, default templates, and seed rules. Operators can edit YAML/JSON manifests before air-gapped deployment. |
 | **Security** | Channel secrets use indirection (`secretRef`), Authority-protected OAuth clients secure API access, and delivery payloads are redacted before storage where required. |