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feat(transport): observability for the import-session cap (register row 53)

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Nothing counted open import sessions and nothing logged a rejection at
MaxConcurrentImportSessions (default 8), so the register-row-43 session leak
could only be inferred from rotating test failures.

- Gauge scadabridge.central.transport.import_sessions.open on the existing
  ZB.MOM.WW.ScadaBridge meter — already in SiteServiceRegistration.ObservedMeters
  (the ZbTelemetryOptions.Meters allowlist), so no telemetry config change is
  needed and the series is not silently dropped. Provider-backed, mirroring the
  StoreAndForward queue-depth gauge: registered by BundleSessionEvictionService
  .StartAsync (Transport's only lifecycle seam) and identity-checked-cleared on
  StopAsync so a late stop cannot clobber a newer registrant.
- IBundleSessionStore.OpenSessionCount counts only UNEXPIRED sessions. The raw
  dictionary count would report the node as pinned at the cap for up to a
  one-minute sweep interval after a burst had drained — the exact false positive
  the instrument exists to rule out.
- BundleSessionStore.Open logs Warning with open count, cap and TTL when it
  rejects. Fires only on a real cap hit: a store full of expired sessions is
  reclaimed first and logs nothing.
- Docs: docs/components/Transport.md + docs/requirements/Component-Transport.md.

Tests: Transport 173 passed (+6 new — Warning content, two negative controls,
unexpired-only counting, gauge register/clear, no-clobber-on-late-stop).
This commit is contained in:
Joseph Doherty
2026-08-15 11:42:31 -04:00
parent b449fe201a
commit 372ea4df1b
7 changed files with 407 additions and 2 deletions
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docs/requirements/Component-Transport.md
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@@ -134,7 +134,7 @@ flowchart TD
class T muted
```
The component is central-hosted. It is registered in `ZB.MOM.WW.ScadaBridge.Host` for central roles only, never for site roles — even when a bundle carries site-scoped config (T18), Transport only writes the central configuration database, never the site clusters. All persistence flows through existing audited repository interfaces in `ZB.MOM.WW.ScadaBridge.ConfigurationDatabase` — the component does not call `DbContext.SaveChangesAsync` directly. `BundleSessionStore` is in-process on the active central node (matching Blazor Server circuit affinity): 30-minute TTL, eviction on expiry, 3-strike passphrase lockout per session, and a `MaxConcurrentImportSessions` cap (default 8; arch-review 05 Task 24 — startup-validated as `> 0` by `TransportOptionsValidator`, since a zero/negative cap would reject every import session forever) bounding the decrypted-content footprint since each open session pins a fully-decrypted bundle in memory.
The component is central-hosted. It is registered in `ZB.MOM.WW.ScadaBridge.Host` for central roles only, never for site roles — even when a bundle carries site-scoped config (T18), Transport only writes the central configuration database, never the site clusters. All persistence flows through existing audited repository interfaces in `ZB.MOM.WW.ScadaBridge.ConfigurationDatabase` — the component does not call `DbContext.SaveChangesAsync` directly. `BundleSessionStore` is in-process on the active central node (matching Blazor Server circuit affinity): 30-minute TTL, eviction on expiry, 3-strike passphrase lockout per session, and a `MaxConcurrentImportSessions` cap (default 8; arch-review 05 Task 24 — startup-validated as `> 0` by `TransportOptionsValidator`, since a zero/negative cap would reject every import session forever) bounding the decrypted-content footprint since each open session pins a fully-decrypted bundle in memory. **The cap is observable (register row 53):** open (unexpired) sessions are published as the `scadabridge.central.transport.import_sessions.open` gauge on the `ZB.MOM.WW.ScadaBridge` meter — already in the `ObservedMeters` allowlist, so no telemetry config change is needed — and a rejection at the cap logs at Warning with the current count, the cap and the TTL. Reclaiming a store full of *expired* sessions is not a cap hit and logs nothing.
**Session release is explicit, not TTL-only (register row 43).** `ApplyAsync` releases the session it applied (zero-then-remove, T-007), and `IBundleImporter.Abandon(sessionId)` does the same for a session that will never be applied. Every abandonment path calls it: the Central UI wizard on new upload / Back-to-Upload / `ResetSessionState` / lockout reset / `Dispose` (navigation away or circuit teardown), the CLI `transport preview` handler (a preview never applies), and the CLI `transport import` handler for the aborts that precede apply (blocker rows, unresolved mappings). `Abandon` is idempotent — double release, an unknown id, and an already-expired id are all silent no-ops — and since session ids are random GUIDs handed only to their opener, abandoning the id you hold can never evict another operator's in-progress import. Relying on the TTL alone was an availability *and* secret-lifetime defect: eight abandoned wizards exhausted `MaxConcurrentImportSessions` and locked out every import on the active node for 30 minutes, each still holding its decrypted bundle content.