diff --git a/internal/cloud/backend-performance.test.ts b/internal/cloud/backend-performance.test.ts
index 32fbd533..26cba64f 100644
--- a/internal/cloud/backend-performance.test.ts
+++ b/internal/cloud/backend-performance.test.ts
@@ -221,6 +221,34 @@ test("backend performance store records Workbench projection and AgentRun result
   assert.doesNotMatch(text, /trc_secret|0123456789abcdef|run_secret|cmd_secret|ses_secret|cnv_secret/u);
 });
 
+test("backend performance reports zero projection lag for caught-up terminal traces", () => {
+  const store = createBackendPerformanceStore({ env: { POD_NAMESPACE: "hwlab-v03", HWLAB_GITOPS_TARGET: "v03", HWLAB_RUNTIME_LANE: "v03", HWLAB_CODE_AGENT_AGENTRUN_PROVIDER_ID: "D601" } });
+
+  store.recordWorkbenchProjection({
+    sourceLatestSeq: 501,
+    lastProjectedSeq: 501,
+    sourceLatestEventAt: "2026-06-19T03:00:00.000Z",
+    projectedLatestEventAt: "2026-06-19T02:00:00.000Z",
+    terminalSourceAt: "2026-06-19T02:00:00.000Z",
+    terminalProjectedAt: "2026-06-19T02:00:00.020Z",
+    status: "completed",
+    reason: "none",
+    projectionStatus: "caught-up",
+    source: "agentrun-v01",
+  });
+
+  const text = store.metricsText();
+  const lagSumLine = text.split("\n").find((line) => line.startsWith("hwlab_workbench_projection_lag_seconds_sum") && line.includes('projection_status="caught_up"'));
+  const lagBucketLine = text.split("\n").find((line) => line.startsWith("hwlab_workbench_projection_lag_seconds_bucket") && line.includes('projection_status="caught_up"') && line.includes('le="0.05"'));
+  const stuckLine = text.split("\n").find((line) => line.startsWith("hwlab_workbench_projection_stuck_traces") && line.includes('projection_status="caught_up"'));
+  const terminalDelayBucketLine = text.split("\n").find((line) => line.startsWith("hwlab_workbench_terminal_projection_delay_seconds_bucket") && line.includes('projection_status="caught_up"') && line.includes('le="0.05"'));
+  assert.ok(lagSumLine);
+  assert.match(lagSumLine, / 0\.000000$/u);
+  assert.ok(lagBucketLine?.endsWith(" 1"));
+  assert.ok(stuckLine?.endsWith(" 0"));
+  assert.ok(terminalDelayBucketLine?.endsWith(" 1"));
+});
+
 test("AgentRun read-side sync advances event cursor without forcing result aggregation before terminal evidence", async () => {
   const calls: string[] = [];
   const agentRunServer = createHttpServer(async (request, response) => {
diff --git a/internal/cloud/backend-performance.ts b/internal/cloud/backend-performance.ts
index ebb347ad..b2c23282 100644
--- a/internal/cloud/backend-performance.ts
+++ b/internal/cloud/backend-performance.ts
@@ -246,7 +246,7 @@ export function createBackendPerformanceStore(options: BackendPerformanceStoreOp
     const sourceAt = unixMs(input.sourceLatestEventAt);
     const projectedAt = unixMs(input.projectedLatestEventAt);
     if (sourceAt !== null && projectedAt !== null) {
-      const lagSeconds = Math.max(0, (sourceAt - projectedAt) / 1000);
+      const lagSeconds = isTerminalProjectionStatus(labels.projection_status) ? 0 : Math.max(0, (sourceAt - projectedAt) / 1000);
       if (!recordHistogram(projectionLagSecondsSeries, labels, lagSeconds, PROJECTION_LAG_SECONDS_BUCKETS, maxSeries)) incrementDropped("projection_lag_seconds_series_limit");
     }
     const terminalSourceAt = unixMs(input.terminalSourceAt);
diff --git a/internal/cloud/server-workbench-http.test.ts b/internal/cloud/server-workbench-http.test.ts
index 1f6cca0e..7aec058b 100644
--- a/internal/cloud/server-workbench-http.test.ts
+++ b/internal/cloud/server-workbench-http.test.ts
@@ -5,6 +5,7 @@ import assert from "node:assert/strict";
 import { test } from "bun:test";
 
 import { createCloudApiServer } from "./server.ts";
+import { createBackendPerformanceStore } from "./backend-performance.ts";
 import { createCodeAgentTraceStore } from "./code-agent-trace-store.ts";
 import { createCodeAgentChatResultStore } from "./server-code-agent-http.ts";
 import { createWorkbenchTurnProjection, projectionDiagnostics } from "./workbench-turn-projection.ts";
@@ -475,7 +476,8 @@ test("workbench read model projects completed current turn for idle session summ
     async ensureBootstrap() {},
     async authenticate() { return { ok: true, actor: ACTOR, session: { id: "uss_workbench_reader" } }; }
   };
-  const server = createCloudApiServer({ accessController, traceStore, codeAgentChatResults: results });
+  const backendPerformanceStore = createBackendPerformanceStore({ env: { POD_NAMESPACE: "hwlab-v03", HWLAB_GITOPS_TARGET: "v03", HWLAB_RUNTIME_LANE: "v03", HWLAB_CODE_AGENT_AGENTRUN_PROVIDER_ID: "D601" } });
+  const server = createCloudApiServer({ accessController, traceStore, codeAgentChatResults: results, backendPerformanceStore });
   await new Promise((resolve) => server.listen(0, "127.0.0.1", resolve));
 
   try {
@@ -501,6 +503,11 @@ test("workbench read model projects completed current turn for idle session summ
     assert.equal(turn.body.projectionStatus, "caught-up");
     assert.equal(turn.body.sourceRunId, "run_workbench_idle_completed");
     assert.equal(turn.body.sourceCommandId, "cmd_workbench_idle_completed");
+    const metricsText = backendPerformanceStore.metricsText();
+    const lagCountLine = metricsText.split("\n").find((line) => line.startsWith("hwlab_workbench_projection_lag_seconds_count") && line.includes('projection_status="caught_up"'));
+    const turnGetCountLine = metricsText.split("\n").find((line) => line.startsWith("hwlab_workbench_turn_get_duration_seconds_count") && line.includes('route="/v1/workbench/turns/:traceId"'));
+    assert.ok(lagCountLine?.endsWith(" 1"));
+    assert.ok(turnGetCountLine?.endsWith(" 1"));
 
     const trace = await getJson(port, `/v1/workbench/traces/${encodeURIComponent(traceId)}/events?limit=10`);
     assert.equal(trace.status, 200);
diff --git a/internal/cloud/server-workbench-http.ts b/internal/cloud/server-workbench-http.ts
index 59384046..c24ced08 100644
--- a/internal/cloud/server-workbench-http.ts
+++ b/internal/cloud/server-workbench-http.ts
@@ -201,6 +201,76 @@ function recordWorkbenchTurnReadMetric(options = {}, url, statusCode, body = {},
   });
 }
 
+function recordWorkbenchProjectionMetric(options = {}, { result = null, trace = null, projection = null, diagnostic = null } = {}) {
+  const performanceStore = options.backendPerformanceStore ?? options.backendPerformance;
+  if (!performanceStore?.recordWorkbenchProjection || !projection) return;
+  const sourceLatestSeq = workbenchProjectionSourceLatestSeq(result, trace, projection);
+  const lastProjectedSeq = Number(diagnostic?.lastProjectedSeq ?? projection?.lastProjectedSeq ?? 0);
+  if (!Number.isFinite(sourceLatestSeq) && !Number.isFinite(lastProjectedSeq)) return;
+  performanceStore.recordWorkbenchProjection({
+    sourceLatestSeq: Number.isFinite(sourceLatestSeq) ? sourceLatestSeq : lastProjectedSeq,
+    lastProjectedSeq: Number.isFinite(lastProjectedSeq) ? lastProjectedSeq : 0,
+    sourceLatestEventAt: workbenchProjectionSourceLatestAt(result, trace, projection),
+    projectedLatestEventAt: diagnostic?.updatedAt ?? projection?.updatedAt ?? trace?.updatedAt ?? result?.updatedAt ?? null,
+    terminalSourceAt: workbenchTerminalSourceAt(result, projection),
+    terminalProjectedAt: diagnostic?.projectionStatus === "caught-up" ? diagnostic?.updatedAt ?? projection?.updatedAt ?? trace?.updatedAt ?? result?.updatedAt ?? null : null,
+    status: projection?.status ?? result?.status ?? trace?.status ?? "unknown",
+    reason: workbenchProjectionReason(diagnostic),
+    projectionStatus: diagnostic?.projectionStatus ?? "unknown",
+    source: result?.agentRun ? "agentrun_v01" : "workbench_read_model"
+  });
+}
+
+function workbenchProjectionSourceLatestSeq(result = null, trace = null, projection = null) {
+  const candidates = [
+    result?.agentRun?.lastSeq,
+    result?.traceSummary?.agentRun?.lastSeq,
+    result?.traceSummary?.lastSeq,
+    result?.providerTrace?.lastSeq,
+    result?.runnerTrace?.lastEvent?.sourceSeq,
+    result?.runnerTrace?.lastEvent?.seq,
+    result?.runnerTrace?.eventCount,
+    trace?.lastSeq,
+    trace?.lastEvent?.sourceSeq,
+    trace?.lastEvent?.seq,
+    trace?.eventCount,
+    projection?.lastProjectedSeq,
+    projection?.eventCount
+  ];
+  for (const value of candidates) {
+    const seq = Number(value);
+    if (Number.isFinite(seq) && seq >= 0) return Math.floor(seq);
+  }
+  return NaN;
+}
+
+function workbenchProjectionSourceLatestAt(result = null, trace = null, projection = null) {
+  return result?.traceSummary?.updatedAt
+    ?? result?.agentRun?.updatedAt
+    ?? result?.providerTrace?.updatedAt
+    ?? result?.runnerTrace?.updatedAt
+    ?? trace?.updatedAt
+    ?? result?.updatedAt
+    ?? projection?.updatedAt
+    ?? null;
+}
+
+function workbenchTerminalSourceAt(result = null, projection = null) {
+  if (projection?.terminal !== true) return null;
+  return result?.traceSummary?.updatedAt
+    ?? result?.agentRun?.updatedAt
+    ?? result?.updatedAt
+    ?? projection?.updatedAt
+    ?? null;
+}
+
+function workbenchProjectionReason(diagnostic = null) {
+  if (diagnostic?.blocker) return diagnostic.blocker.code ?? "projection_blocked";
+  if (diagnostic?.projectionStatus === "projecting") return "projecting";
+  if (diagnostic?.projectionStatus === "caught-up") return "none";
+  return diagnostic?.projectionStatus ?? "unknown";
+}
+
 function workbenchTurnDegradedReason(body = {}) {
   if (body?.projection?.blocker?.code) return body.projection.blocker.code;
   if (body?.blocker?.code) return body.blocker.code;
@@ -342,6 +412,7 @@ async function handleWorkbenchTurnSnapshot(response, url, options, actor, rawTur
     return sendJson(response, 404, body);
   }
   const projection = readModel.projectionDiagnostics({ traceId, result, trace, projection: turnProjection });
+  recordWorkbenchProjectionMetric(options, { result, trace, projection: turnProjection, diagnostic: projection });
   const body = {
     ok: true,
     status,
@@ -379,6 +450,7 @@ async function handleWorkbenchTraceEventPage(response, url, options, actor, rawT
   const page = traceEventPage(trace, tracePageOptions(url));
   const turnProjection = createWorkbenchTurnProjection({ traceId, result, session, trace });
   const projection = readModel.projectionDiagnostics({ traceId, result, trace, projection: turnProjection });
+  recordWorkbenchProjectionMetric(options, { result, trace, projection: turnProjection, diagnostic: projection });
   sendJson(response, 200, {
     ok: true,
     status: "succeeded",