fix(server): let agents watch reopened pull requests

apps/server/src/mcp/McpHttpServer.test.ts

@@ -15,6 +15,8 @@ import { McpProtocol, McpSchema, McpServer } from "effect/unstable/ai";
 import { HttpBody, HttpClient, HttpRouter, HttpServerResponse } from "effect/unstable/http";
 
 import * as ProjectService from "../project/ProjectService.ts";
+import * as PullRequestService from "../pullRequest/PullRequestService.ts";
+import * as PullRequestWatchReactor from "../orchestration-v2/PullRequestWatchReactor.ts";
 import * as ServerConfig from "../config.ts";
 import * as McpHttpServer from "./McpHttpServer.ts";
 import * as McpInvocationContext from "./McpInvocationContext.ts";
@@ -52,12 +54,14 @@ const TestLayer = McpHttpServer.PreviewToolkitRegistrationLive.pipe(
   Layer.provideMerge(NodeServices.layer),
 );
 const PullRequestsTestLayer = McpHttpServer.PullRequestsToolkitRegistrationLive.pipe(
+  Layer.provide(PullRequestWatchReactor.layer),
   Layer.provideMerge(McpServer.McpServer.layer),
   Layer.provide(
     Layer.mergeAll(
       Layer.mock(ProjectService.ProjectService)({}),
       Layer.mock(Orchestrator.OrchestratorV2)({}),
       Layer.mock(ProjectionStore.ProjectionStoreV2)({}),
+      Layer.mock(PullRequestService.PullRequestService)({}),
       NodeServices.layer,
     ),
   ),

apps/server/src/mcp/toolkits/pullRequests/handlers.test.ts

@@ -2,6 +2,7 @@ import {
   EnvironmentId,
   ProjectId,
   ProviderInstanceId,
+  PullRequestOperationError,
   ThreadId,
   type OrchestrationV2ServerCommand as OrchestrationCommand,
   type OrchestrationProjectShell,
@@ -22,6 +23,9 @@ import {
   v2PullRequestThread,
 } from "../../../orchestration-v2/testkit/pullRequestFixtures.ts";
 import * as ProjectService from "../../../project/ProjectService.ts";
+import * as PullRequestService from "../../../pullRequest/PullRequestService.ts";
+import * as PullRequestWatchReactor from "../../../orchestration-v2/PullRequestWatchReactor.ts";
+import * as ProjectionStore from "../../../orchestration-v2/ProjectionStore.ts";
 import * as McpInvocationContext from "../../McpInvocationContext.ts";
 import { listThreadPullRequests, PullRequestsToolkitHandlersLive } from "./handlers.ts";
 import { PullRequestLinkFailedError, PullRequestsToolkit } from "./tools.ts";
@@ -126,6 +130,7 @@ function makeLink(
 interface HarnessOptions {
   readonly thread?: PullRequestTestThread | null;
   readonly project?: OrchestrationProjectShell | null;
+  readonly summary?: PullRequestService.PullRequestService["Service"]["summary"];
   /** A rejection the orchestrator reports as the dispatch error's cause. */
   readonly reject?: (command: OrchestrationCommand) => string | null;
 }
@@ -134,8 +139,24 @@ const makeHarness = Effect.fn("makePullRequestsToolkitHarness")(function* (
   options: HarnessOptions = {},
 ) {
   const commands = yield* Ref.make<ReadonlyArray<OrchestrationCommand>>([]);
+  const reads = yield* Ref.make<ReadonlyArray<string>>([]);
   const thread = options.thread === undefined ? makeThread([]) : options.thread;
   const project = options.project === undefined ? makeProject() : options.project;
+  const summary: PullRequestService.PullRequestService["Service"]["summary"] =
+    options.summary ??
+    ((input) =>
+      Effect.succeed({
+        provider: "github",
+        projectId: input.projectId,
+        repository: input.repository,
+        number: input.number,
+        title: "Reopened PR",
+        url: `https://github.com/${input.repository}/pull/${input.number}`,
+        state: "open",
+        headBranch: "feature",
+        baseBranch: "main",
+        updatedAt: "2026-08-28T00:00:00.000Z",
+      }));
   const dispatch: Orchestrator.OrchestratorV2Shape["dispatch"] = (command) =>
     Effect.gen(function* () {
       const rejection = options.reject?.(command) ?? null;
@@ -148,7 +169,8 @@ const makeHarness = Effect.fn("makePullRequestsToolkitHarness")(function* (
       yield* Ref.update(commands, (recorded) => [...recorded, command]);
       return { sequence: 1, storedEvents: [] };
     });
-  const dependencies = Layer.mergeAll(
+  const baseDependencies = Layer.mergeAll(
+    Layer.mock(ProjectionStore.ProjectionStoreV2)({}),
     Layer.mock(ProjectService.ProjectService)({
       getShell: () => Effect.succeed(Option.fromNullishOr(project)),
     }),
@@ -157,8 +179,20 @@ const makeHarness = Effect.fn("makePullRequestsToolkitHarness")(function* (
         Effect.succeed(id === THREAD_ID && thread ? v2PullRequestThread(thread) : null),
       dispatch,
     }),
+    Layer.mock(PullRequestService.PullRequestService)({
+      invalidate: () => Ref.update(reads, (calls) => [...calls, "invalidate"]),
+      summary: (input, options) =>
+        Ref.update(reads, (calls) => [...calls, "summary"]).pipe(
+          Effect.andThen(
+            options?.recoverTransientFailure === false && input.allowStale === false
+              ? summary(input, options)
+              : Effect.die("Watch refresh must not return stale PR state"),
+          ),
+        ),
+    }),
     Layer.succeed(Crypto.Crypto, testCrypto),
   );
+  const dependencies = PullRequestWatchReactor.layer.pipe(Layer.provideMerge(baseDependencies));
   const toolkit = yield* PullRequestsToolkit.pipe(
     Effect.provide(PullRequestsToolkitHandlersLive.pipe(Layer.provide(dependencies))),
   );
@@ -177,7 +211,7 @@ const makeHarness = Effect.fn("makePullRequestsToolkitHarness")(function* (
       Effect.provideService(McpInvocationContext.McpInvocationContext, invocation(capabilities)),
       Effect.provide(dependencies),
     );
-  return { commands, call };
+  return { commands, reads, call };
 });
 
 describe("pull request toolkit handlers", () => {
@@ -271,6 +305,76 @@ describe("pull request toolkit handlers", () => {
       expect(yield* Ref.get(harness.commands)).toMatchObject([
         { type: "thread.pull-request.watch", number: 3, watching: false },
       ]);
+      expect(yield* Ref.get(harness.reads)).toEqual([]);
+    }),
+  );
+
+  it.effect("starts watching a reopened PR after refreshing its closed snapshot", () =>
+    Effect.gen(function* () {
+      const link = makeLink(7, { headBranch: "feature" });
+      const harness = yield* makeHarness({
+        thread: makeThread([
+          { ...link, snapshot: link.snapshot && { ...link.snapshot, state: "closed" } },
+        ]),
+      });
+      yield* harness.call("watch_pull_request", { repository: "t3tools/t3code", number: 7 });
+      expect(yield* Ref.get(harness.reads)).toEqual(["invalidate", "summary"]);
+      expect(yield* Ref.get(harness.commands)).toMatchObject([
+        { type: "thread.pull-request-link.sync", number: 7, snapshot: { state: "open" } },
+        { type: "thread.pull-request.watch", number: 7, watching: true },
+      ]);
+    }),
+  );
+
+  it.effect("refuses a PR that remains closed on the host", () =>
+    Effect.gen(function* () {
+      const link = makeLink(7, { headBranch: "feature" });
+      const harness = yield* makeHarness({
+        thread: makeThread([
+          { ...link, snapshot: link.snapshot && { ...link.snapshot, state: "closed" } },
+        ]),
+        summary: (input) =>
+          Effect.succeed({
+            provider: "github",
+            projectId: input.projectId,
+            repository: input.repository,
+            number: input.number,
+            title: "Closed PR",
+            url: link.url,
+            state: "closed",
+            headBranch: "feature",
+            baseBranch: "main",
+            updatedAt: "2026-08-28T00:00:00.000Z",
+          }),
+      });
+      const error = yield* harness
+        .call("watch_pull_request", { repository: "t3tools/t3code", number: 7 })
+        .pipe(Effect.flip);
+      expect(error).toMatchObject({ _tag: "PullRequestNotOpenError", state: "closed" });
+      expect(yield* Ref.get(harness.commands)).toMatchObject([
+        { type: "thread.pull-request-link.sync", number: 7, snapshot: { state: "closed" } },
+      ]);
+    }),
+  );
+
+  it.effect("reports a failed host refresh without starting a watch", () =>
+    Effect.gen(function* () {
+      const link = makeLink(7, { headBranch: "feature" });
+      const failure = new PullRequestOperationError({
+        operation: "summary",
+        detail: "Host offline",
+      });
+      const harness = yield* makeHarness({
+        thread: makeThread([
+          { ...link, snapshot: link.snapshot && { ...link.snapshot, state: "closed" } },
+        ]),
+        summary: () => Effect.fail(failure),
+      });
+      const error = yield* harness
+        .call("watch_pull_request", { repository: "t3tools/t3code", number: 7 })
+        .pipe(Effect.flip);
+      expect(error).toMatchObject({ _tag: "PullRequestWatchFailedError", cause: failure });
+      expect(yield* Ref.get(harness.commands)).toEqual([]);
     }),
   );
 

apps/server/src/mcp/toolkits/pullRequests/handlers.ts

@@ -25,6 +25,7 @@ import * as Option from "effect/Option";
 
 import * as Orchestrator from "../../../orchestration-v2/Orchestrator.ts";
 import * as ProjectService from "../../../project/ProjectService.ts";
+import * as PullRequestWatchReactor from "../../../orchestration-v2/PullRequestWatchReactor.ts";
 import * as McpInvocationContext from "../../McpInvocationContext.ts";
 import {
   type ListThreadPullRequestsResult,
@@ -34,7 +35,6 @@ import {
   PullRequestHostRequiredError,
   PullRequestUnlinkFailedError,
   PullRequestListFailedError,
-  PullRequestNotOpenError,
   type PullRequestTargetInput,
   PullRequestWatchFailedError,
   PullRequestThreadNotFoundError,
@@ -152,6 +152,7 @@ export function listThreadPullRequests(
 
 const make = Effect.gen(function* () {
   const engine = yield* Orchestrator.OrchestratorV2;
+  const watches = yield* PullRequestWatchReactor.PullRequestWatchReactor;
 
   const projects = yield* ProjectService.ProjectService;
   const crypto = yield* Crypto.Crypto;
@@ -220,17 +221,8 @@ const make = Effect.gen(function* () {
     const thread = yield* requireThread(PullRequestWatchFailedError);
     const project = yield* projectOf(thread, PullRequestWatchFailedError);
     const target = yield* resolveTarget(input, project);
-    const watchedLink = (shell: OrchestrationV2ThreadShell) =>
-      threadPullRequestsOf(shell).find(
-        (link) => link.source !== "stack-dismissed" && threadPullRequestKeysEqual(link, target),
-      );
-    const before = watchedLink(thread);
-    const state = before?.snapshot?.state;
-    if (watching && state !== undefined && state !== "open") {
-      return yield* new PullRequestNotOpenError({ state });
-    }
-    yield* engine
-      .dispatch({
+    const result = yield* watches
+      .setWatching({
         type: "thread.pull-request.watch",
         commandId: yield* commandId("mcp-pr-watch", thread.id),
         threadId: thread.id,
@@ -240,15 +232,19 @@ const make = Effect.gen(function* () {
         watching,
         ...(watching ? { link: { url: target.url, source: "agent" as const } } : {}),
       })
-      .pipe(Effect.catchCause(dispatchFailure(PullRequestWatchFailedError)));
-    const after = yield* requireThread(PullRequestWatchFailedError);
+      .pipe(
+        Effect.mapError((cause) =>
+          cause._tag === "PullRequestNotOpenError"
+            ? cause
+            : new PullRequestWatchFailedError({ cause }),
+        ),
+      );
     return {
       host: target.host,
       repository: target.repository,
       number: target.number,
       url: target.url,
-      watching: watchedLink(after)?.watch !== undefined,
-      wasWatching: before?.watch !== undefined,
+      ...result,
     };
   });
 

apps/server/src/mcp/toolkits/pullRequests/tools.ts

@@ -12,11 +12,13 @@ import * as Toolkit from "effect/unstable/ai/Toolkit";
 import * as McpInvocationContext from "../../McpInvocationContext.ts";
 import * as Orchestrator from "../../../orchestration-v2/Orchestrator.ts";
 import * as ProjectService from "../../../project/ProjectService.ts";
+import * as PullRequestWatchReactor from "../../../orchestration-v2/PullRequestWatchReactor.ts";
 
 const dependencies = [
   McpInvocationContext.McpInvocationContext,
   Orchestrator.OrchestratorV2,
   ProjectService.ProjectService,
+  PullRequestWatchReactor.PullRequestWatchReactor,
 ];
 
 const REGISTER_EVERY_PR =
@@ -117,15 +119,6 @@ export class PullRequestWatchFailedError extends Schema.TaggedError<PullRequestW
   }
 }
 
-export class PullRequestNotOpenError extends Schema.TaggedError<PullRequestNotOpenError>()(
-  "PullRequestNotOpenError",
-  { state: Schema.String },
-) {
-  override get message(): string {
-    return `The pull request is ${this.state}, so there is nothing to watch.`;
-  }
-}
-
 export class PullRequestListFailedError extends Schema.TaggedError<PullRequestListFailedError>()(
   "PullRequestListFailedError",
   { cause: Schema.Defect() },
@@ -145,7 +138,7 @@ export const PullRequestToolError = Schema.Union([
   PullRequestUnlinkFailedError,
   PullRequestListFailedError,
   PullRequestWatchFailedError,
-  PullRequestNotOpenError,
+  PullRequestWatchReactor.PullRequestNotOpenError,
 ]);
 export type PullRequestToolError = typeof PullRequestToolError.Type;
 

apps/server/src/mcp/toolkits/worktree/registration.test.ts

@@ -1,5 +1,6 @@
 import * as Orchestrator from "../../../orchestration-v2/Orchestrator.ts";
 import * as ProjectionStore from "../../../orchestration-v2/ProjectionStore.ts";
+import * as PullRequestWatchReactor from "../../../orchestration-v2/PullRequestWatchReactor.ts";
 import * as DeviceService from "../../../device/DeviceService.ts";
 import * as ServerConfig from "../../../config.ts";
 import { expect, it } from "@effect/vitest";
@@ -28,6 +29,7 @@ import * as PreviewAutomationBroker from "../../PreviewAutomationBroker.ts";
 const StubServicesLive = Layer.mergeAll(
   Layer.mock(Orchestrator.OrchestratorV2)({}),
   Layer.mock(ProjectionStore.ProjectionStoreV2)({}),
+  Layer.mock(PullRequestWatchReactor.PullRequestWatchReactor)({}),
   Layer.mock(DeviceService.DeviceService)({}),
   Layer.mock(ThreadManagementService.ThreadManagementService)({}),
   Layer.mock(ProviderRegistry.ProviderRegistry)({}),

apps/server/src/orchestration-v2/PullRequestSyncReactor.ts

@@ -43,7 +43,7 @@ interface LinkEntry {
   readonly link: ThreadPullRequestLink;
 }
 
-function snapshotFieldsOf(summary: PullRequestSummary): SnapshotFields {
+export function snapshotFieldsOf(summary: PullRequestSummary): SnapshotFields {
   return {
     state: summary.state,
     title: summary.title,