diff --git a/web/hwlab-cloud-web/scripts/check.ts b/web/hwlab-cloud-web/scripts/check.ts
index ec50e00f..4285c2c6 100644
--- a/web/hwlab-cloud-web/scripts/check.ts
+++ b/web/hwlab-cloud-web/scripts/check.ts
@@ -100,8 +100,7 @@ assertIncludes(appSource, "useForm", "form composable must remain available for
 assertIncludes(appSource, "hwlab_session", "auth comments/code must preserve Web session cookie boundary");
 assertIncludes(appSource, "activityRef", "Code Agent inactivity-timeout activityRef must be preserved");
 assertIncludes(workbenchStoreSource, "connectWorkbenchEvents", "Workbench must use the unified SSE realtime entry");
-assertIncludes(workbenchStoreSource, "scheduleRealtimeGapHydration", "Workbench realtime disconnect/reconnect must trigger REST gap fill");
-assertIncludes(workbenchStoreSource, "hydrateRealtimeGap", "Workbench realtime recovery must use REST snapshot/page gap fill");
+assert.doesNotMatch(workbenchStoreSource, /scheduleRealtimeGapHydration|hydrateRealtimeGap/u, "Workbench realtime consumer must not repair projection through REST gap fill");
 assert.doesNotMatch(workbenchStoreSource, /subscribeToTrace|TRACE_POLL_INTERVAL_MS/u, "Workbench store must not reintroduce active trace polling");
 assertIncludes(appSource, "/v1/workbench/events", "Workbench realtime client must use the RESTful same-origin events endpoint");
 assertIncludes(appSource, "/v1/workbench/traces/", "trace hydration must use Workbench read-model trace API");
diff --git a/web/hwlab-cloud-web/scripts/workbench-server-state.test.ts b/web/hwlab-cloud-web/scripts/workbench-server-state.test.ts
index 508e4d1f..f45d22c1 100644
--- a/web/hwlab-cloud-web/scripts/workbench-server-state.test.ts
+++ b/web/hwlab-cloud-web/scripts/workbench-server-state.test.ts
@@ -103,3 +103,30 @@ test("Workbench server-state session detail updates session status authority", (
   assert.equal(authority?.status, "completed");
   assert.equal(authority?.lastTraceId, "trc_backfill");
 });
+
+test("Workbench realtime agent snapshots cannot create duplicate assistant messages", () => {
+  let state = createWorkbenchServerState();
+  state = reduceWorkbenchServerState(state, {
+    type: "session.messages",
+    sessionId: "ses_steer",
+    messages: [
+      { id: "msg_user", messageId: "msg_user", role: "user", title: "用户", text: "ping", status: "sent", createdAt: "2026-06-24T00:00:00.000Z", sessionId: "ses_steer", traceId: "trc_steer_target" },
+      { id: "msg_agent", messageId: "msg_agent", role: "agent", title: "Code Agent", text: "", status: "running", createdAt: "2026-06-24T00:00:01.000Z", sessionId: "ses_steer", traceId: "trc_steer_target" }
+    ]
+  });
+
+  state = reduceWorkbenchServerState(state, {
+    type: "message.snapshot",
+    sessionId: "ses_steer",
+    message: { id: "msg_agent", messageId: "msg_agent", role: "agent", title: "Code Agent", text: "done", status: "completed", createdAt: "2026-06-24T00:00:01.000Z", sessionId: "ses_steer", traceId: "trc_steer_target" }
+  });
+  assert.deepEqual(selectActiveMessages(state, "ses_steer").map((message) => `${message.role}:${message.messageId}:${message.text}`), ["user:msg_user:ping", "agent:msg_agent:done"]);
+
+  state = reduceWorkbenchServerState(state, {
+    type: "message.snapshot",
+    sessionId: "ses_steer",
+    message: { id: "msg_duplicate_agent", messageId: "msg_duplicate_agent", role: "agent", title: "Code Agent", text: "projection-resume:non-terminal-backoff", status: "completed", createdAt: "2026-06-24T00:00:02.000Z", sessionId: "ses_steer", traceId: "trc_duplicate" }
+  });
+
+  assert.deepEqual(selectActiveMessages(state, "ses_steer").map((message) => message.messageId), ["msg_user", "msg_agent"]);
+});
diff --git a/web/hwlab-cloud-web/src/stores/workbench-server-state.ts b/web/hwlab-cloud-web/src/stores/workbench-server-state.ts
index 4e585690..626dc9fc 100644
--- a/web/hwlab-cloud-web/src/stores/workbench-server-state.ts
+++ b/web/hwlab-cloud-web/src/stores/workbench-server-state.ts
@@ -148,6 +148,7 @@ function reduceMessageSnapshot(state: WorkbenchServerState, sessionId: string |
   if (!id || !message) return state;
   const existing = state.messagesBySessionId[id] ?? state.sessionsById[id]?.messages ?? [];
   const index = existing.findIndex((item) => messageMatchesSnapshot(item, message));
+  if (index < 0 && message.role === "agent") return state;
   const merged = index >= 0
     ? existing.map((item, itemIndex) => itemIndex === index ? mergeMessageSnapshot(item, message) : item)
     : [...existing, message];
diff --git a/web/hwlab-cloud-web/src/stores/workbench.ts b/web/hwlab-cloud-web/src/stores/workbench.ts
index 33b62cc0..0fbb983b 100644
--- a/web/hwlab-cloud-web/src/stores/workbench.ts
+++ b/web/hwlab-cloud-web/src/stores/workbench.ts
@@ -502,6 +502,7 @@ export const useWorkbenchStore = defineStore("workbench", () => {
     return {
       ok: false,
       status: 503,
+      data: null,
       error: message,
       apiError: {
         code: "workbench_read_hydration_cooldown",
@@ -528,6 +529,7 @@ export const useWorkbenchStore = defineStore("workbench", () => {
     return {
       ok: false,
       status: 0,
+      data: null,
       error: message,
       apiError: {
         code: "workbench_read_hydration_throttled",
@@ -770,9 +772,13 @@ function nonBlockingProjection(projection: ProjectionDiagnostic | null): Project
     const threadId = composer.value.threadId;
     const providerThreadId = providerThreadIdForRequest(threadId);
     const submittedAt = new Date().toISOString();
-    const user = makeMessage("user", value, "sent", { traceId: steerTraceId ?? traceId, sessionId, threadId, title: steerMode ? "用户引导" : "用户", createdAt: submittedAt, updatedAt: submittedAt });
-    const pending = makeMessage("agent", "", "running", { traceId, sessionId, threadId, title: "Code Agent", retryInput: value, traceAutoLifecycle: "running", createdAt: submittedAt, updatedAt: submittedAt, ...optimisticRunningTimingPatch(submittedAt) });
-    appendActiveMessages(user, pending);
+    const previousChatPending = chatPending.value;
+    if (!steerMode) {
+      const user = makeMessage("user", value, "sent", { traceId, sessionId, threadId, title: "用户", createdAt: submittedAt, updatedAt: submittedAt });
+      const pending = makeMessage("agent", "", "running", { traceId, sessionId, threadId, title: "Code Agent", retryInput: value, traceAutoLifecycle: "running", createdAt: submittedAt, updatedAt: submittedAt, ...optimisticRunningTimingPatch(submittedAt) });
+      appendActiveMessages(user, pending);
+      projectOptimisticRunningTurn({ sessionId, threadId, traceId, userText: value });
+    }
     startWorkbenchSubmitJourney({ traceId, sessionId, entry: submitEntry, backend: providerProfile.value, transport: "sse" });
     chatPending.value = true;
     rememberRecentDraft(value);
@@ -784,6 +790,14 @@ function nonBlockingProjection(projection: ProjectionDiagnostic | null): Project
       const projection = projectionDiagnosticFromApiFailure(response, { code: "code_agent_admission_failed", message: response.error ?? "Code Agent 请求失败", health: response.status === 0 ? "unavailable" : "degraded" });
       const failureError = agentErrorFromApiFailure(response, projection, "Code Agent 请求失败");
       const failureMessage = agentErrorDisplayText(failureError) ?? "Code Agent 请求失败";
+      if (steerMode) {
+        error.value = failureMessage;
+        applyProjectionDiagnostic(traceId, projection);
+        failWorkbenchSubmitJourney(traceId, response.status === 0 ? "network" : "error");
+        chatPending.value = previousChatPending;
+        restartRealtime("steer-not-admitted");
+        return false;
+      }
       markMessage(traceId, { status: "failed", text: failureMessage, error: failureError, projection, projectionStatus: projection.projectionStatus ?? null, projectionHealth: projection.projectionHealth ?? null, blocker: projection.blocker ?? null });
       applyProjectionDiagnostic(traceId, projection);
       reduceServerState({ type: "turn.forget", traceId });
@@ -1385,7 +1399,7 @@ function nonBlockingProjection(projection: ProjectionDiagnostic | null): Project
     const status = existing?.status ?? normalizedStatusText(message?.status) ?? null;
     const running = existing?.running === true || (!isTerminalMessageStatus(message?.status) && isTraceActiveStatus(message?.status));
     const now = new Date().toISOString();
-    reduceServerState({ type: "turn.status", turn: { traceId, status, running, terminal: existing?.terminal === true, sessionId, threadId: firstNonEmptyString(message?.threadId, message?.runnerTrace?.threadId) ?? existing?.threadId ?? null, updatedAt: now, projection, loadedAt: now } });
+    reduceServerState({ type: "turn.status", turn: { traceId, status, running, terminal: false, sessionId, threadId: firstNonEmptyString(message?.threadId, message?.runnerTrace?.threadId) ?? existing?.threadId ?? null, updatedAt: now, projection, loadedAt: now } });
     if (sessionId) reduceServerState({ type: "session.status", session: { sessionId, status: activeSession.value?.status ?? status, updatedAt: now, lastTraceId: traceId, projection, loadedAt: now } });
     const projectionError = agentErrorFromProjection(projection);
     updateActiveMessages((source) => source.map((item) => {
@@ -1855,7 +1869,7 @@ function messageStatusPatchForTerminalMerge(message: ChatMessage, resultStatus:
 function firstPositiveFiniteNumber(...values: unknown[]): number | null {
   for (const value of values) {
     const number = firstFiniteNumber(value);
-    if (number !== null && number > 0) return number;
+    if (number !== undefined && number > 0) return number;
   }
   return null;
 }