Heartbeats fire every 60s per workspace and were the dominant caller
of ReadPlatformInboundSecret — one DB SELECT each, purely to redeliver
the same value. For an N-workspace fleet that's N SELECTs/minute of
pure overhead, growing linearly with the fleet (#189).
This adds a sync.Map cache keyed by workspaceID with a 5-minute TTL:
- **Read-through**: cache miss → DB SELECT → populate → return.
- **Write-through**: every IssuePlatformInboundSecret call refreshes
the cache with the new value before returning, so the lazy-heal mint
path (readOrLazyHealInboundSecret) doesn't see a stale read of the
value it just wrote.
- **TTL eviction**: 5 minutes — generous enough that the heartbeat
hot path hits cache for ~5 reads in a row before re-validating, short
enough that an out-of-band rotation (operator running
`UPDATE workspaces SET platform_inbound_secret=...` directly)
propagates within minutes without requiring a redeploy.
- **Absence not cached**: ErrNoInboundSecret skips the cache write so
the lazy-heal recovery contract for the column-NULL case
(readOrLazyHealInboundSecret in workspace_provision_shared.go) keeps
working.
Memory footprint is bounded by the active workspace fleet (~200 bytes
per entry); deleted workspaces leave dead entries until process restart,
acceptable given workspace-deletion is operator-rare.
Why in-process instead of Redis: workspace-server runs as a single
Railway service today (per memory project_controlplane_ownership);
adding Redis for this single column read would be over-engineering.
The cache is a self-contained, Redis-free upgrade that keeps the same
semantic surface (read returns the latest secret) while collapsing
the heartbeat read storm. If the deployment ever fans out across
replicas, an operator-side rotation propagates per-replica TTL-bounded
without needing a shared write log.
Tests: 5 new cases covering cache hit within TTL, refresh after TTL
(simulating an operator rotation via SQL), write-through on Issue,
absence-not-cached, and Reset clearing all entries. The setupMock
helper in wsauth and setupTestDB helper in handlers both call
ResetInboundSecretCacheForTesting() at start + cleanup so write-through
state from one test doesn't shadow SELECT expectations in the next.
SetInboundSecretCacheNowForTesting() exposes a deterministic clock
override so the TTL test doesn't sleep.
Task: #189.
b040171fa1