fix(ui): refuse late open/attach replies after terminal connection dispose (#128147)

ui/src/components/terminal/terminal-connection.test.ts

@@ -970,4 +970,33 @@ describe("TerminalConnection", () => {
     expect(client.listenerCount()).toBe(0);
     expect(conn.size).toBe(0);
   });
+
+  // A reply that lands after panel teardown races a dead owner. Registering its
+  // stream would retain the sink forever and arm the liveness probe loop
+  // against the replaced client, so the owner must refuse post-dispose work.
+  it.each([
+    ["attach", "terminal.attach"],
+    ["open", "terminal.open"],
+  ] as const)(
+    "a late %s reply after dispose() leaves no resurrected stream or liveness probes",
+    (kind, method) =>
+      withFakeTimers(async () => {
+        const { client, conn } = makeHarness();
+        const response = createDeferred<TestSessionResult & { buffer: string }>();
+        deferRequest(client, method, response);
+        const settle =
+          kind === "attach"
+            ? conn.attach("s1", testSink())
+            : conn.open({ cols: 80, rows: 24 }, testSink());
+        // Panel teardown (reconnect or element removal) discards the connection
+        // while the RPC is still in flight.
+        conn.dispose();
+        response.resolve({ ...sessionResult(), buffer: "replayed\n" });
+        await expect(settle).resolves.toMatchObject({ sessionId: "s1" });
+        expect(conn.size).toBe(0);
+        expect(client.listenerCount()).toBe(0);
+        await vi.advanceTimersByTimeAsync(IDLE_PLUS_PROBE_MS);
+        expect(client.requests.filter((request) => request.method === "terminal.list")).toEqual([]);
+      }),
+  );
 });

ui/src/components/terminal/terminal-connection.ts

@@ -140,6 +140,10 @@ export class TerminalConnection {
   // capped buffer becomes a detectable gap instead of silent output loss.
   private readonly pending = new Map<string, BoundedBuffer<PendingEvent>>();
   private unsubscribe: (() => void) | null = null;
+  // Fence for replies that outlive dispose(): without it a late open/attach
+  // would resurrect stream state and re-arm the liveness loop on a connection
+  // whose panel is gone or was replaced by a reconnect.
+  private disposed = false;
   private pendingOpenCount = 0;
   private livenessTimer: ReturnType<typeof setTimeout> | null = null;
   private livenessProbeInFlight = false;
@@ -244,6 +248,9 @@ export class TerminalConnection {
       }
       throw new TerminalOpenUnusableSessionError(missingField);
     }
+    if (this.disposed) {
+      return result;
+    }
     const stream = this.setStream(result.sessionId, sink, {
       seqMode: "unknown",
       expectedSeq: 0,
@@ -268,6 +275,9 @@ export class TerminalConnection {
     }
     const offset =
       typeof result.seq === "number" && Number.isSafeInteger(result.seq) ? result.seq : null;
+    if (this.disposed) {
+      return result;
+    }
     const stream = this.setStream(sessionId, sink, {
       seqMode: offset === null ? "counter" : "offset",
       expectedSeq: offset,
@@ -640,6 +650,7 @@ export class TerminalConnection {
   }
 
   dispose(): void {
+    this.disposed = true;
     for (const stream of this.streams.values()) {
       stream.abort.abort();
     }