Closes Stream D per docs/v2/implementation/phase-6-1-resilience-and-observability.md.
New Configuration.LocalCache types (alongside the existing single-file
LiteDbConfigCache):
- GenerationSealedCache — file-per-generation sealed snapshots per decision
#148. Each SealAsync writes <cache-root>/<clusterId>/<generationId>.db as a
read-only LiteDB file, then atomically publishes the CURRENT pointer via
temp-file + File.Replace. Prior-generation files stay on disk for audit.
Mixed-generation reads are structurally impossible: ReadCurrentAsync opens
the single file named by CURRENT. Corruption of the pointer or the sealed
file raises GenerationCacheUnavailableException — fails closed, never falls
back silently to an older generation. TryGetCurrentGenerationId returns the
pointer value or null for diagnostics.
- StaleConfigFlag — thread-safe (Volatile.Read/Write) bool. MarkStale when a
read fell back to the cache; MarkFresh when a central-DB read succeeded.
Surfaced on /healthz body and Admin /hosts (Stream C wiring already in
place).
- ResilientConfigReader — wraps a central-DB fetch function with the Stream
D.2 pipeline: timeout 2 s → retry N× jittered (skipped when retryCount=0) →
fallback to the sealed cache. Toggles StaleConfigFlag per outcome. Read path
only — the write path is expected to bypass this wrapper and fail hard on
DB outage so inconsistent writes never land. Cancellation passes through
and is NOT retried.
Configuration.csproj:
- Polly.Core 8.6.6 + Microsoft.Extensions.Logging.Abstractions added.
Tests (17 new, all pass):
- GenerationSealedCacheTests (10): first-boot-no-snapshot throws
GenerationCacheUnavailableException (D.4 scenario C), seal-then-read round
trip, sealed file is ReadOnly on disk, pointer advances to latest, prior
generation file preserved, corrupt sealed file fails closed, missing sealed
file fails closed, corrupt pointer fails closed (D.4 scenario B), same
generation sealed twice is idempotent, independent clusters don't
interfere.
- ResilientConfigReaderTests (4): central-DB success returns value + marks
fresh; central-DB failure exhausts retries + falls back to cache + marks
stale (D.4 scenario A); central-DB + cache both unavailable throws;
cancellation not retried.
- StaleConfigFlagTests (3): default is fresh; toggles; concurrent writes
converge.
Full solution dotnet test: 1033 passing (baseline 906, +127 net across Phase
6.1 Streams A/B/C/D). Pre-existing Client.CLI Subscribe flake unchanged.
Integration into Configuration read paths (DriverInstance enumeration,
LdapGroupRoleMapping fetches, etc.) + the sp_PublishGeneration hook that
writes sealed files lands in the Phase 6.1 Stream E / Admin-refresh PR where
the DB integration surfaces are already touched. Existing LiteDbConfigCache
continues serving its single-file role for the NodeBootstrap path.
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
