fix(anpr): share one camera snapshot across bridge + advisory paths

On a vehicle entry, two paths captured the SAME Hikvision camera within ~1s —
the ANPR bridge (barrier-driving) and the advisory snapshotAsync (evidence/
telemetry) — each from a separate adapter instance. Hikvision serves snapshots
single-threaded, so the second concurrent GET returned HTTP 503; the bridge
then fail-softed and burned its 12s debounce, producing a ~74s "slow" subscriber
entry (observed 2026-06-25, Qazim Mulleti / AB816NN — plate read was instant at
conf 1.000; the delay was the 503/debounce churn, not recognition).

Add captureSnapshotShared() in snapshot.ts: a module-level, deviceId-keyed cache
that both paths call. It coalesces in-flight captures (the 2nd caller awaits the
1st's pull → no concurrent 503), serves a brief freshness window (1500ms) so the
bridge→advisory sequence for one vehicle reuses one frame, never caches a failure
(next caller retries), and keys by deviceId (no cross-camera/stale-vehicle reuse).
Wired into anpr-entry.ts (bridge) and snapshot.ts (advisory).

Tests: snapshot.test.ts (concurrent coalescing, TTL reuse, TTL-lapse re-pull,
failure-not-cached, per-camera keying); anpr-entry.test.ts mock updated. 168
server tests green.

NOTE: this removes the latency (the 503 collision). The separate double-entry
(two signed vehicle_entry for one car) — debounce-too-short / stamp-before-
success — is still open; less likely now but not eliminated.

Claude-Session: https://claude.ai/code/session_01Xcm6ikLgGoCxxHrxtjkk5V

apps/server/src/anpr-entry.ts

@@ -3,7 +3,7 @@ import { devices, deviceEvents as deviceEventsTable, eq, siteConfig, type Db, ty
 import type { FastifyBaseLogger } from "fastify";
 import { deviceEvents, type DeviceReadEvent } from "./device-events.js";
 import { directionOf, type FlowDirection } from "./device-resolve.js";
-import { buildCamera } from "./snapshot.js";
+import { buildCamera, captureSnapshotShared } from "./snapshot.js";
 import type { SubscriptionFlow } from "./subscription-flow.js";
 import type { VisionClient } from "./vision-client.js";
 
@@ -100,7 +100,9 @@ export class AnprBridge {
       // "both" collapses to entry purely for the capture hint (it doesn't pick the lane —
       // the gated flow infers the verb from the camera's bound relay direction).
       const direction: FlowDirection = directionOf(this.#db, row) === "exit" ? "exit" : "entry";
-      const shot = await camera.captureSnapshot({ direction });
+      // Shared capture (deviceId-keyed): coalesces with the advisory snapshotAsync for
+      // the SAME vehicle so the single-threaded camera isn't hit twice (→ HTTP 503).
+      const shot = await captureSnapshotShared(deviceId, camera, { direction });
       const result = await this.#vision.analyze(shot.bytes, shot.contentType);
       if (!result || !result.plate) return; // nothing read