diff --git a/apps/server/src/orchestration-v2/PullRequestWatchReactor.ts b/apps/server/src/orchestration-v2/PullRequestWatchReactor.ts
index f37a69c08ee0..5ff0d42ecf8f 100644
--- a/apps/server/src/orchestration-v2/PullRequestWatchReactor.ts
+++ b/apps/server/src/orchestration-v2/PullRequestWatchReactor.ts
@@ -298,7 +298,7 @@ export const make = Effect.gen(function* () {
 
   const giveUp = (target: WatchTarget) =>
     record(target, null, {
-      text: `T3 Code stopped watching pull request #${target.link.number} (${target.link.url}) because it failed to read it from the host ${READ_FAILURE_LIMIT} times in a row. Check it yourself, and call watch_pull_request to watch it again.`,
+      text: `T3 Code stopped watching pull request #${target.link.number} (${target.link.url}) because it failed to read it from the host ${READ_FAILURE_LIMIT} times in a row. Check it yourself, and call watch_pull_request only if it is still open.`,
       notification: {
         source: { kind: "monitor" },
         outcome: "failed",
@@ -491,11 +491,14 @@ export const make = Effect.gen(function* () {
       { concurrency: 2 },
     );
     // Activity failures must not cancel or hide a permanent detail failure.
+    // Activity is irrelevant once the pull request is closed or merged, so it cannot block ending.
     const read = Exit.isFailure(detailRead)
       ? Exit.failCause(detailRead.cause)
-      : Exit.isFailure(activityRead)
-        ? Exit.failCause(activityRead.cause)
-        : Exit.succeed([detailRead.value, activityRead.value] as const);
+      : detailRead.value.state !== "open"
+        ? Exit.succeed([detailRead.value, Option.none<PullRequestActivity>()] as const)
+        : Exit.isFailure(activityRead)
+          ? Exit.failCause(activityRead.cause)
+          : Exit.succeed([detailRead.value, activityRead.value] as const);
     if (Exit.isFailure(read)) {
       if (Cause.hasInterruptsOnly(read.cause)) return yield* Effect.failCause(read.cause);
       lastReads.delete(group.key);
diff --git a/apps/server/src/orchestration-v2/runtimeLayer.test.ts b/apps/server/src/orchestration-v2/runtimeLayer.test.ts
index a49e323770cc..4b978ab36093 100644
--- a/apps/server/src/orchestration-v2/runtimeLayer.test.ts
+++ b/apps/server/src/orchestration-v2/runtimeLayer.test.ts
@@ -3434,6 +3434,75 @@ it.layer(layerTest)("OrchestrationV2LayerLive lifecycle", (it) => {
       }),
   );
 
+  it.effect("ends a watch on a closed pull request whose activity cannot be read", () =>
+    Effect.gen(function* () {
+      const orchestrator = yield* Orchestrator.OrchestratorV2;
+      const threadId = ThreadId.make("runtime-pull-request-watch-closed-unreadable");
+      const projectId = ProjectId.make("pr-watch-closed-unreadable-project");
+      yield* seedProject({
+        projectId,
+        title: "Watch closed unreadable",
+        workspaceRoot: "/workspace/watch-closed-unreadable",
+        defaultModelSelection: null,
+        createdAt: "2026-10-01T00:00:00.000Z",
+      });
+      yield* orchestrator.dispatch({
+        type: "thread.create",
+        createdBy: "user",
+        creationSource: "web",
+        commandId: CommandId.make("pr-watch-closed-unreadable-create"),
+        threadId,
+        projectId,
+        title: "Watch closed unreadable",
+        modelSelection,
+        runtimeMode: "full-access",
+        interactionMode: "default",
+        branch: null,
+        worktreePath: null,
+      });
+      yield* orchestrator.dispatch({
+        type: "thread.pull-request.watch",
+        commandId: CommandId.make("pr-watch-closed-unreadable-start"),
+        threadId,
+        host: "github.com",
+        repository: "pingdotgg/t3code",
+        number: 8,
+        watching: true,
+        link: { url: "https://github.com/pingdotgg/t3code/pull/8", source: "agent" },
+      });
+      const reactor = yield* PullRequestWatchReactor.make.pipe(
+        Effect.provide(
+          Layer.mergeAll(
+            NodeServices.layer,
+            NodeCrypto.layer,
+            Layer.mock(PullRequestService.PullRequestService)({
+              watchFingerprint: () => Effect.succeed(null),
+              detail: () =>
+                Effect.succeed({
+                  ...watchedPullRequestDetail({
+                    projectId,
+                    number: 8,
+                    at: "2026-10-02T12:00:00.000Z",
+                  }),
+                  state: "closed" as const,
+                }),
+              activity: () => Effect.die("host unreachable"),
+            }),
+          ),
+        ),
+      );
+      yield* reactor.sweep;
+
+      const thread = yield* orchestrator.getThreadShell(threadId);
+      assert.isUndefined(thread?.pullRequests?.[0]?.watch);
+      const { messages } = yield* orchestrator.getThreadRecords(threadId, ["messages"]);
+      assert.deepEqual(
+        messages.flatMap((message) => message.notification?.summary ?? []),
+        ["#8: closed, stopped watching"],
+      );
+    }),
+  );
+
   it.effect("wakes once for a state it reported, across a restart and a new watch", () =>
     Effect.gen(function* () {
       const orchestrator = yield* Orchestrator.OrchestratorV2;