fix: keep channel typing active during long inference (#25886, thanks @stakeswky)

Co-authored-by: stakeswky <stakeswky@users.noreply.github.com>

src/channels/typing.ts

@@ -10,9 +10,15 @@ export function createTypingCallbacks(params: {
   stop?: () => Promise<void>;
   onStartError: (err: unknown) => void;
   onStopError?: (err: unknown) => void;
+  keepaliveIntervalMs?: number;
 }): TypingCallbacks {
   const stop = params.stop;
-  const onReplyStart = async () => {
+  const keepaliveIntervalMs = params.keepaliveIntervalMs ?? 3_000;
+  let keepaliveTimer: ReturnType<typeof setInterval> | undefined;
+  let keepaliveStartInFlight = false;
+  let stopSent = false;
+
+  const fireStart = async () => {
     try {
       await params.start();
     } catch (err) {
@@ -20,11 +26,41 @@ export function createTypingCallbacks(params: {
     }
   };
 
-  const fireStop = stop
-    ? () => {
-        void stop().catch((err) => (params.onStopError ?? params.onStartError)(err));
+  const clearKeepalive = () => {
+    if (!keepaliveTimer) {
+      return;
+    }
+    clearInterval(keepaliveTimer);
+    keepaliveTimer = undefined;
+    keepaliveStartInFlight = false;
+  };
+
+  const onReplyStart = async () => {
+    stopSent = false;
+    clearKeepalive();
+    await fireStart();
+    if (keepaliveIntervalMs <= 0) {
+      return;
+    }
+    keepaliveTimer = setInterval(() => {
+      if (keepaliveStartInFlight) {
+        return;
       }
-    : undefined;
+      keepaliveStartInFlight = true;
+      void fireStart().finally(() => {
+        keepaliveStartInFlight = false;
+      });
+    }, keepaliveIntervalMs);
+  };
+
+  const fireStop = () => {
+    clearKeepalive();
+    if (!stop || stopSent) {
+      return;
+    }
+    stopSent = true;
+    void stop().catch((err) => (params.onStopError ?? params.onStartError)(err));
+  };
 
   return { onReplyStart, onIdle: fireStop, onCleanup: fireStop };
 }