fix: bind extensions for web sessions

Fixes #19

.changeset/bind-session-extensions.md

@@ -0,0 +1,5 @@
+---
+"@jmfederico/pi-web": patch
+---
+
+Initialize Pi extensions for web-managed sessions so `session_start` handlers, extension resources, and startup-dependent tools run correctly.

src/server/sessions/piSessionService.test.ts

@@ -45,8 +45,9 @@ function sessionRecord(id: string, cwd = "/workspace") {
 
 function fakeRuntime(sessionId = "session-1", patch: Partial<TestSession> = {}) {
   const promptCalls: { text: string; options: unknown }[] = [];
+  const bindExtensionCalls: unknown[] = [];
   const listeners: ((event: unknown) => void)[] = [];
-  const calls = { abort: 0, clearQueue: 0, dispose: 0, prompt: promptCalls };
+  const calls = { abort: 0, bindExtensions: bindExtensionCalls, clearQueue: 0, dispose: 0, prompt: promptCalls };
   const session: TestSession = {
     sessionId,
     sessionFile: `/tmp/${sessionId}.jsonl`,
@@ -71,6 +72,10 @@ function fakeRuntime(sessionId = "session-1", patch: Partial<TestSession> = {})
         if (index !== -1) listeners.splice(index, 1);
       };
     },
+    bindExtensions: (bindings: unknown) => {
+      calls.bindExtensions.push(bindings);
+      return Promise.resolve();
+    },
     getSessionStats: () => ({ sessionId, totalMessages: 0, userMessages: 0, assistantMessages: 0, toolCalls: 0, tokens: { input: 0, output: 0, cacheRead: 0, cacheWrite: 0, total: 0 }, cost: 0 }),
     getContextUsage: () => undefined,
     prompt: (text: string, options: unknown) => {
@@ -146,6 +151,7 @@ describe("PiSessionService", () => {
     const session = await service.start("/workspace");
 
     expect(createCalls).toBe(1);
+    expect(fake.calls.bindExtensions).toHaveLength(1);
     expect(session).toMatchObject({ id: "session-1", cwd: "/workspace", messageCount: 0 });
     expect(service.activeCount()).toBe(1);
     expect(hub.globalEvents.some((event) => event.type === "status.update" && event.status.sessionId === "session-1")).toBe(true);
@@ -155,6 +161,59 @@ describe("PiSessionService", () => {
     expect(fake.calls.dispose).toBe(1);
   });
 
+  it("binds extensions again when the SDK runtime replaces the active session", async () => {
+    const hub = new CapturingSessionEventHub();
+    const fake = fakeRuntime("session-1");
+    const replacement = fakeRuntime("session-2");
+    let rebindSession: ((session: PiAgentSession) => Promise<void>) | undefined;
+    fake.runtime.setRebindSession = (callback) => { rebindSession = callback; };
+    const service = new PiSessionService(hub, {
+      createAgentRuntime: runtimeCreator(fake.runtime),
+      sessionManager: sessionGateway([]),
+      heartbeatIntervalMs: 60_000,
+    });
+
+    await service.start("/workspace");
+    Object.defineProperty(fake.runtime, "session", { configurable: true, value: replacement.session });
+    await rebindSession?.(replacement.session);
+
+    expect(fake.calls.bindExtensions).toHaveLength(1);
+    expect(replacement.calls.bindExtensions).toHaveLength(1);
+    expect(service.activeCount()).toBe(1);
+    expect(await service.status("session-2")).toMatchObject({ sessionId: "session-2" });
+
+    await service.dispose();
+  });
+
+  it("publishes extension errors reported while binding session extensions", async () => {
+    const hub = new CapturingSessionEventHub();
+    const fake = fakeRuntime("extension-session", {
+      bindExtensions: (bindings) => {
+        bindings.onError?.({ extensionPath: "pi-mcp-adapter", event: "session_start", error: "MCP failed" });
+        return Promise.resolve();
+      },
+    });
+    const service = new PiSessionService(hub, {
+      createAgentRuntime: runtimeCreator(fake.runtime),
+      sessionManager: sessionGateway([]),
+      heartbeatIntervalMs: 60_000,
+    });
+
+    await service.start("/workspace");
+
+    expect(hub.sessionEvents).toContainEqual({
+      sessionId: "extension-session",
+      event: { type: "session.error", message: "pi-mcp-adapter: MCP failed" },
+    });
+    const extensionErrorActivity = hub.globalEvents.find((event) => event.type === "activity.update" && event.activity.sessionId === "extension-session");
+    expect(extensionErrorActivity).toMatchObject({
+      type: "activity.update",
+      activity: { sessionId: "extension-session", phase: "error", label: "extension error", detail: "pi-mcp-adapter: MCP failed" },
+    });
+
+    await service.dispose();
+  });
+
   it("clears stale active activity once a previously active session becomes idle", async () => {
     vi.useFakeTimers();
     let service: PiSessionService | undefined;

src/server/sessions/piSessionService.ts

@@ -89,6 +89,17 @@ export interface PiSessionManagerGateway {
   open(path: string): PiSessionManager;
 }
 
+interface PiExtensionError {
+  extensionPath: string;
+  event: string;
+  error: string;
+  stack?: string;
+}
+
+interface PiExtensionBindings {
+  onError?: (error: PiExtensionError) => void;
+}
+
 export interface PiAgentSession {
   modelRegistry: ModelRegistryInstance;
   sessionManager: PiSessionManager;
@@ -107,6 +118,7 @@ export interface PiAgentSession {
   promptTemplates: readonly { name: string; description?: string }[];
   resourceLoader: { getSkills(): { skills: readonly { name: string; description?: string }[] } };
   subscribe(listener: (event: unknown) => void): () => void;
+  bindExtensions(bindings: PiExtensionBindings): Promise<void>;
   compact(instructions?: string): Promise<{ summary: string; tokensBefore: number }>;
   getUserMessagesForForking(): readonly { entryId: string; text: string }[];
   getSessionStats(): { sessionId: string; totalMessages: number; userMessages: number; assistantMessages: number; toolCalls: number; tokens: ClientSessionStatus["tokens"]; cost: number };
@@ -642,17 +654,28 @@ export class PiSessionService {
 
   private async create(sessionManager: PiSessionManager, cwd: string): Promise<ActiveSession<PiSessionRuntime>> {
     const runtime = await this.createAgentRuntime(this.createRuntime, { cwd, agentDir: this.agentDir, sessionManager });
+    await this.bindSessionExtensions(runtime.session);
     const active: ActiveSession<PiSessionRuntime> = { runtime, unsubscribe: noop };
     this.bindRuntime(active);
-    runtime.setRebindSession(() => {
+    runtime.setRebindSession(async (session) => {
+      await this.bindSessionExtensions(session);
       this.bindRuntime(active);
-      return Promise.resolve();
     });
     this.active.set(runtime.session.sessionId, active);
     this.publishStatus(runtime.session);
     return active;
   }
 
+  private async bindSessionExtensions(session: PiAgentSession): Promise<void> {
+    await session.bindExtensions({
+      onError: (error) => {
+        const message = `${error.extensionPath}: ${error.error}`;
+        this.publishActivity(session, "extension error", "error", message);
+        this.events.publish(session.sessionId, { type: "session.error", message });
+      },
+    });
+  }
+
   private bindRuntime(active: ActiveSession<PiSessionRuntime>): void {
     active.unsubscribe();
     const { session } = active.runtime;