fix(chat): catch ProcessTransport errors on interrupt

When the SDK child process has already exited, calling interrupt() throws
"ProcessTransport is not ready for writing" as an unhandled rejection,
crashing the server. Wrap the call in try/catch — if the transport is
dead the interrupt is moot anyway.

Also add .catch() to the fire-and-forget interruptChat() call in
ws-handler-v2 to prevent any future unhandled rejections from that path.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: dimakis

server/chat.ts

@@ -1273,7 +1273,16 @@ export async function interruptChat(
       );
       await Promise.allSettled(stops);
     }
-    await session.queryInstance.interrupt();
+    try {
+      await session.queryInstance.interrupt();
+    } catch (err: unknown) {
+      // ProcessTransport may already be dead (process exited) — the interrupt
+      // is moot in that case.  Swallow rather than crashing the server.
+      log.warn('interrupt() failed (transport likely dead)', {
+        clientId,
+        err: err instanceof Error ? err.message : String(err),
+      });
+    }
     // Only push to inputQueue on first delivery — a retried interrupt should
     // still call interrupt() (to halt the agent) but not double-queue the prompt.
     if (!isDup) {

server/ws-handler-v2.ts

@@ -733,6 +733,12 @@ export function handleInterruptV2(
           msg.contextBlocks,
           msg.clientMsgId,
           msg.model,
+        ).catch((err: unknown) =>
+          log.error('interruptChat failed', {
+            connectionId,
+            sessionId: msg.sessionId,
+            err: err instanceof Error ? err.message : String(err),
+          }),
         );
         log.info('interrupt', { connectionId, sessionId: msg.sessionId });
         return;