feat: add heartbeat visibility filtering for webchat

- Add isHeartbeat to AgentRunContext to track heartbeat runs
- Pass isHeartbeat flag through agent runner execution
- Suppress webchat broadcast (deltas + final) for heartbeat runs when showOk is false
- Webchat uses channels.defaults.heartbeat settings (no per-channel config)
- Default behavior: hide HEARTBEAT_OK from webchat (matches other channels)

This allows users to control whether heartbeat responses appear in
the webchat UI via channels.defaults.heartbeat.showOk (defaults to false).

src/gateway/server-chat.ts

@@ -1,8 +1,28 @@
 import { normalizeVerboseLevel } from "../auto-reply/thinking.js";
+import { loadConfig } from "../config/config.js";
 import { type AgentEventPayload, getAgentRunContext } from "../infra/agent-events.js";
+import { resolveHeartbeatVisibility } from "../infra/heartbeat-visibility.js";
 import { loadSessionEntry } from "./session-utils.js";
 import { formatForLog } from "./ws-log.js";
 
+/**
+ * Check if webchat broadcasts should be suppressed for heartbeat runs.
+ * Returns true if the run is a heartbeat and showOk is false.
+ */
+function shouldSuppressHeartbeatBroadcast(runId: string): boolean {
+  const runContext = getAgentRunContext(runId);
+  if (!runContext?.isHeartbeat) return false;
+
+  try {
+    const cfg = loadConfig();
+    const visibility = resolveHeartbeatVisibility({ cfg, channel: "webchat" });
+    return !visibility.showOk;
+  } catch {
+    // Default to suppressing if we can't load config
+    return true;
+  }
+}
+
 export type ChatRunEntry = {
   sessionKey: string;
   clientRunId: string;
@@ -130,7 +150,10 @@ export function createAgentEventHandler({
         timestamp: now,
       },
     };
-    broadcast("chat", payload, { dropIfSlow: true });
+    // Suppress webchat broadcast for heartbeat runs when showOk is false
+    if (!shouldSuppressHeartbeatBroadcast(clientRunId)) {
+      broadcast("chat", payload, { dropIfSlow: true });
+    }
     nodeSendToSession(sessionKey, "chat", payload);
   };
 
@@ -158,7 +181,10 @@ export function createAgentEventHandler({
             }
           : undefined,
       };
-      broadcast("chat", payload);
+      // Suppress webchat broadcast for heartbeat runs when showOk is false
+      if (!shouldSuppressHeartbeatBroadcast(clientRunId)) {
+        broadcast("chat", payload);
+      }
       nodeSendToSession(sessionKey, "chat", payload);
       return;
     }