diff --git a/src/gateway/server-methods/chat.error-broadcast.test.ts b/src/gateway/server-methods/chat.error-broadcast.test.ts
new file mode 100644
index 00000000000..dba4ba3b4d7
--- /dev/null
+++ b/src/gateway/server-methods/chat.error-broadcast.test.ts
@@ -0,0 +1,65 @@
+import { describe, expect, it, vi } from "vitest";
+import { chatHandlers } from "./chat.js";
+import type { GatewayRequestContext } from "./types.js";
+
+function createMockContext() {
+  const broadcast = vi.fn();
+  const nodeSendToSession = vi.fn();
+  const chatAbortControllers = new Map();
+  const agentRunSeq = new Map<string, number>();
+  const dedupe = new Map();
+
+  return {
+    broadcast,
+    nodeSendToSession,
+    chatAbortControllers,
+    agentRunSeq,
+    dedupe,
+    logGateway: { warn: vi.fn(), debug: vi.fn(), error: vi.fn() },
+    addChatRun: vi.fn(),
+    removeChatRun: vi.fn(),
+  };
+}
+
+describe("chat.send error broadcast", () => {
+  it("should broadcast error when addChatRun throws", async () => {
+    const ctx = createMockContext();
+    const respond = vi.fn();
+
+    // Make addChatRun throw synchronously (inside the try block at line 2470)
+    ctx.addChatRun.mockImplementation(() => {
+      throw Object.assign(new Error("LLM timeout"), { code: "TIMEOUT" });
+    });
+
+    await chatHandlers["chat.send"]({
+      params: {
+        sessionKey: "main",
+        message: "hello",
+        idempotencyKey: "test-run-1",
+      },
+      respond: respond as never,
+      context: ctx as unknown as GatewayRequestContext,
+      req: {} as never,
+      client: null as never,
+      isWebchatConnect: () => false,
+    });
+
+    // Verify respond was called with error
+    expect(respond).toHaveBeenCalledWith(
+      false,
+      expect.objectContaining({ runId: "test-run-1", status: "error" }),
+      expect.any(Object),
+      expect.any(Object),
+    );
+
+    // Verify broadcastChatError was called (via context.broadcast)
+    expect(ctx.broadcast).toHaveBeenCalledWith(
+      "chat",
+      expect.objectContaining({
+        runId: "test-run-1",
+        state: "error",
+        errorMessage: expect.stringContaining("LLM timeout"),
+      }),
+    );
+  });
+});
diff --git a/src/gateway/server-methods/chat.ts b/src/gateway/server-methods/chat.ts
index 7c8d9392754..7b74147e865 100644
--- a/src/gateway/server-methods/chat.ts
+++ b/src/gateway/server-methods/chat.ts
@@ -3178,6 +3178,12 @@ export const chatHandlers: GatewayRequestHandlers = {
         runId: clientRunId,
         error: formatForLog(err),
       });
+      broadcastChatError({
+        context,
+        runId: clientRunId,
+        sessionKey,
+        errorMessage: String(err),
+      });
     }
   },
   "chat.inject": async ({ params, respond, context }) => {