fix: expose workbench cache observability

internal/cloud/server-workbench-http.ts

@@ -300,6 +300,25 @@ function recordWorkbenchTurnReadMetric(options = {}, url, statusCode, body = {},
   });
 }
 
+function recordWorkbenchCacheMetric(options = {}, url, body = {}, startedAt = nowMs()) {
+  const performanceStore = options.backendPerformanceStore ?? options.backendPerformance;
+  if (!performanceStore?.recordWorkbenchCache) return;
+  const cache = body?.cache && typeof body.cache === "object" ? body.cache : null;
+  if (!cache) return;
+  performanceStore.recordWorkbenchCache({
+    route: url?.pathname ?? "/v1/workbench",
+    cacheKeyClass: cache.class,
+    cacheStatus: cache.status,
+    operation: "read",
+    durationMs: nowMs() - startedAt,
+    payloadBytes: cache.payloadBytes,
+    cacheAgeMs: cache.cacheAgeMs,
+    dbQueryAvoided: cache.dbQueryAvoided,
+    freshnessSloMs: cache.freshnessSloMs,
+    projectionSeq: cache.projectionSeq
+  });
+}
+
 function recordWorkbenchProjectionMetric(options = {}, { result = null, trace = null, projection = null, diagnostic = null } = {}) {
   const performanceStore = options.backendPerformanceStore ?? options.backendPerformance;
   if (!performanceStore?.recordWorkbenchProjection || !projection) return;
@@ -405,6 +424,7 @@ async function authenticateWorkbenchRead(request, response, options) {
 }
 
 async function handleWorkbenchSessionList(request, response, url, options, actor) {
+  const startedAt = nowMs();
   if (url.searchParams.has("projectId") || url.searchParams.has("workspaceId")) return sendJson(response, 400, workbenchError("workbench_authority_removed", "Workbench session list is keyed by sessionId only."));
   const limit = boundedSessionListLimit(url.searchParams.get("limit"));
   const offset = cursorOffset(url.searchParams.get("cursor") ?? url.searchParams.get("after"));
@@ -421,6 +441,7 @@ async function handleWorkbenchSessionList(request, response, url, options, actor
     includeSessionId: includeRouteId ?? null,
     actor: { id: actor.id, role: actor.role ?? "user", valuesRedacted: true }
   });
+  recordWorkbenchCacheMetric(options, url, payload, startedAt);
   return sendJson(response, 200, payload);
 }
 
@@ -1147,6 +1168,7 @@ async function handleWorkbenchTurnSnapshot(response, url, options, actor, rawTur
     contractVersion: "workbench-turn-snapshot-v1",
     turn: snapshot,
     projection,
+    cache: result.cache ?? null,
     projectionStatus: projection.projectionStatus,
     projectionHealth: projection.projectionHealth,
     lastProjectedSeq: projection.lastProjectedSeq,
@@ -1162,10 +1184,12 @@ async function handleWorkbenchTurnSnapshot(response, url, options, actor, rawTur
     diagnostic: projection
   });
   recordWorkbenchTurnReadMetric(options, url, 200, body, startedAt);
+  recordWorkbenchCacheMetric(options, url, body, startedAt);
   sendJson(response, 200, body);
 }
 
 async function handleWorkbenchTraceEventPage(response, url, options, actor, rawTraceId) {
+  const startedAt = nowMs();
   const traceId = safeTraceId(rawTraceId);
   if (!traceId) return sendJson(response, 400, workbenchError("invalid_trace_id", "traceId must start with trc_.", { traceId: rawTraceId }));
   const readModel = createWorkbenchReadModel(options, actor);
@@ -1199,7 +1223,7 @@ async function handleWorkbenchTraceEventPage(response, url, options, actor, rawT
     page.blocker = blocker;
   }
   const responseProjection = page.blocker ? blockedTraceEventProjection(projection, page.blocker) : projection;
-  sendJson(response, 200, {
+  const body = {
     ok: true,
     status: page.blocker ? "blocked" : "succeeded",
     contractVersion: "workbench-trace-events-v1",
@@ -1208,6 +1232,7 @@ async function handleWorkbenchTraceEventPage(response, url, options, actor, rawT
     threadId: safeOpaqueId(session?.threadId) ?? (textValue(session?.threadId) || null),
     ...page,
     projection: responseProjection,
+    cache: pageResult.cache ?? metadata.cache ?? null,
     projectionStatus: responseProjection.projectionStatus,
     projectionHealth: responseProjection.projectionHealth,
     lastProjectedSeq: responseProjection.lastProjectedSeq,
@@ -1222,7 +1247,9 @@ async function handleWorkbenchTraceEventPage(response, url, options, actor, rawT
     durationMs: responseProjection.durationMs,
     valuesRedacted: true,
     secretMaterialStored: false
-  });
+  };
+  recordWorkbenchCacheMetric(options, url, body, startedAt);
+  sendJson(response, 200, body);
 }
 
 function traceEventPageFromFacts(sourceEvents, options, metadata = {}) {