fix(node): reject sendAndWait on session shutdown

Treat session.shutdown as a terminal outcome while waiting for a response, including when the send RPC itself remains pending.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Author: connor4312

nodejs/src/session.ts

@@ -750,6 +750,10 @@ export class CopilotSession {
         const outcomePromise = new Promise<SessionOutcome>((resolve) => {
             resolveOutcome = resolve;
         });
+        let resolveShutdown: (error: Error) => void;
+        const shutdownPromise = new Promise<Error>((resolve) => {
+            resolveShutdown = resolve;
+        });
 
         let lastAssistantMessage: AssistantMessageEvent | undefined;
 
@@ -764,12 +768,24 @@ export class CopilotSession {
                 const error = new Error(event.data.message);
                 error.stack = event.data.stack;
                 resolveOutcome({ kind: "error", error });
+            } else if (event.type === "session.shutdown") {
+                const reason = event.data.errorReason ? `: ${event.data.errorReason}` : "";
+                const error = new Error(
+                    `Session ${this.sessionId} shut down before becoming idle${reason}`
+                );
+                resolveOutcome({ kind: "error", error });
+                resolveShutdown(error);
             }
         });
 
         let timeoutId: ReturnType<typeof setTimeout> | undefined;
         try {
-            await this.send(options);
+            await Promise.race([
+                this.send(options),
+                shutdownPromise.then((error) => {
+                    throw error;
+                }),
+            ]);
 
             const timeoutPromise = new Promise<never>((_, reject) => {
                 timeoutId = setTimeout(

nodejs/test/session-send-and-wait.test.ts

@@ -29,6 +29,23 @@ function errorEvent(message: string): SessionEvent {
     } as SessionEvent;
 }
 
+function shutdownEvent(errorReason?: string): SessionEvent {
+    return {
+        type: "session.shutdown",
+        id: "00000000-0000-4000-8000-000000000002",
+        parentId: null,
+        timestamp: new Date().toISOString(),
+        data: {
+            codeChanges: { filesModified: [], linesAdded: 0, linesRemoved: 0 },
+            errorReason,
+            modelMetrics: {},
+            sessionStartTime: Date.now(),
+            shutdownType: errorReason ? "error" : "routine",
+            totalApiDurationMs: 0,
+        },
+    } as SessionEvent;
+}
+
 function controlledSession(): {
     session: CopilotSession;
     sendStarted: Promise<void>;
@@ -134,4 +151,16 @@ describe("sendAndWait", () => {
         errorFirst.resolveSend();
         await expect(errorFirstPending).rejects.toThrow("first error");
     });
+
+    it("rejects when the session shuts down before becoming idle", async () => {
+        const { session, sendStarted } = controlledSession();
+        const pending = session.sendAndWait({ prompt: "hi" });
+        await sendStarted;
+
+        session._dispatchEvent(shutdownEvent("runtime session was lost"));
+
+        await expect(pending).rejects.toThrow(
+            "Session session-1 shut down before becoming idle: runtime session was lost"
+        );
+    });
 });