prep docs and service updates

docs/airgap/prep/2025-11-20-staleness-drift-prep.md

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+# Staleness & Drift Prep — PREP-AIRGAP-CTL-58-001-BLOCKED-ON-57-002
+
+Status: Draft (2025-11-20)
+Owners: AirGap Controller Guild · AirGap Time Guild
+Scope: Capture the staleness/drift requirements for controller status once seal/unseal telemetry (57-002) is available.
+
+## Inputs
+- Time anchor ingestion from Time service (Roughtime/RFC3161) via `time_anchor_id`, `drift_seconds`, `staleness_budget_seconds`.
+- Bundle metadata from importer (bundle_id, manifest hash, generated_at).
+
+## Proposed status enrichments
+- Add fields to `GET /system/airgap/status`:
+  - `staleness_seconds_remaining`
+  - `bundle_id`
+  - `time_anchor_id`
+  - `drift_seconds`
+- Compute `staleness_seconds_remaining = staleness_budget_seconds - drift_seconds` (floor at 0).
+- Determinism: calculations purely from stored numbers; no wall-clock calls beyond persisted anchor timestamps.
+
+## Observability
+- Metrics: `airgap_staleness_seconds{tenant}` (gauge), `airgap_drift_seconds{tenant}`.
+- Timeline events emitted when budgets breached: `airgap.staleness.threshold`.
+
+## Handoff
+Use this prep note to satisfy PREP-AIRGAP-CTL-58-001. After integrating sealed-startup telemetry and time anchor verification, implement the above fields and metrics, then mark the implementation task DOING.