fix(#529): latch child 'initialized' events so a same-chunk arrival can't stall adoption

src/proxy/child-session-manager.ts

@@ -177,6 +177,10 @@ export class ChildSessionManager extends EventEmitter {
   // State tracking
   private adoptionInProgress = false;
   private sawChildStop = false;
+  // Latched in wireChildEvents: an 'initialized' event can arrive in the same
+  // socket chunk as the request's response, i.e. before any waitForEvent
+  // listener registered by the response's awaiter exists (issue #529)
+  private childInitializedCount = 0;
   // An adopted child's connection closed and no new adoption has started
   // since — routed commands can only hit the parent, where child-required
   // ones (e.g. js-debug 'pause') would silently no-op (issue #513)
@@ -547,11 +551,16 @@ export class ChildSessionManager extends EventEmitter {
       // Configure child session
       await death.race(this.configureChild(child, pendingId, parentConfig));
 
-      // Attach to pending target
+      // Attach to pending target. Snapshot the 'initialized' latch first:
+      // js-debug can deliver the post-attach 'initialized' in the same socket
+      // chunk as the attach response, and a listener registered only after
+      // attachChild resolves would miss it — stalling adoption 3s and pushing
+      // the CDP bridge attach past the entry pause (issue #529)
+      const postAttachInitBaseline = this.childInitializedCount;
       await this.attachChild(child, pendingId, parentConfig, death);
 
       // Handle post-attach initialization if needed
-      await death.race(this.handlePostAttachInit(child));
+      await death.race(this.handlePostAttachInit(child, postAttachInitBaseline));
 
       // Connect the CDP function-breakpoint bridge BEFORE forcing the entry
       // pause so the proxy's sticky Debugger.paused replay plus a live
@@ -631,10 +640,12 @@ export class ChildSessionManager extends EventEmitter {
     };
 
     logger.info(`[child:${pendingId}] initialize`);
+    const initializedBaseline = this.childInitializedCount;
     await child.sendRequest('initialize', initArgs);
-
-    // Wait for initialized event
-    await this.waitForEvent(child, 'initialized', this.dapBehavior.childInitTimeout || 12000);
+
+    // Wait for initialized event (latched — it may have arrived with the
+    // initialize response itself, issue #529)
+    await this.waitForChildInitialized(child, initializedBaseline, this.dapBehavior.childInitTimeout || 12000);
   }
 
   /**
@@ -869,11 +880,13 @@ export class ChildSessionManager extends EventEmitter {
   }
 
   /**
-   * Handle post-attach initialization (some adapters emit another 'initialized')
+   * Handle post-attach initialization (some adapters emit another 'initialized').
+   * `initializedBaseline` is the latch count snapshotted before the attach
+   * request was sent, so an event that raced the attach response still counts.
    */
-  private async handlePostAttachInit(child: MinimalDapClient): Promise<void> {
+  private async handlePostAttachInit(child: MinimalDapClient, initializedBaseline: number): Promise<void> {
     // Wait briefly for a post-attach initialized event
-    const sawPostInit = await this.waitForEvent(child, 'initialized', 3000, false);
+    const sawPostInit = await this.waitForChildInitialized(child, initializedBaseline, 3000, false);
 
     if (sawPostInit && this.dapBehavior.mirrorBreakpointsToChild) {
       // Re-send configuration after post-attach initialized
@@ -946,6 +959,9 @@ export class ChildSessionManager extends EventEmitter {
       if (evt.event === 'stopped') {
         this.sawChildStop = true;
       }
+      if (evt.event === 'initialized') {
+        this.childInitializedCount++;
+      }
       const bridge = this.cdpBridge;
       if (!bridge) {
         // Forward child events through parent
@@ -987,6 +1003,28 @@ export class ChildSessionManager extends EventEmitter {
     });
   }
 
+  /**
+   * Wait until the child has emitted more 'initialized' events than
+   * `baseline`. The count is latched in wireChildEvents from connect time, so
+   * an event delivered in the same socket chunk as a request's response —
+   * dispatched before the response's awaiter could register a listener — is
+   * not lost (issue #529; same shape as the #515 init-ACK latch). The latch
+   * check and waitForEvent's listener registration share one synchronous
+   * frame, so no event can slip between them.
+   */
+  private waitForChildInitialized(
+    child: MinimalDapClient,
+    baseline: number,
+    timeoutMs: number,
+    required: boolean = true
+  ): Promise<boolean> {
+    if (this.childInitializedCount > baseline) {
+      logger.info(`[ChildSessionManager:${this.instanceId}] 'initialized' already latched (count=${this.childInitializedCount}); skipping wait`);
+      return Promise.resolve(true);
+    }
+    return this.waitForEvent(child, 'initialized', timeoutMs, required);
+  }
+
   /**
    * Wait for a specific event with timeout
    */

tests/proxy/child-session-manager.test.ts

@@ -31,6 +31,10 @@ class MockMinimalDapClient extends EventEmitter {
   // Emit a post-attach 'initialized' (some adapters re-initialize after
   // attach; drives handlePostAttachInit's replay path)
   static emitInitializedAfterAttach = false;
+  // Commands that emit 'initialized' synchronously during sendRequest, i.e.
+  // before the caller's await resumes — models the event arriving in the same
+  // socket chunk as the response (issue #529)
+  static emitInitializedSyncOn = new Set<string>();
   // When set, returned verbatim for 'threads'
   static threadsResponse: unknown | undefined = undefined;
   // When true, shutdown() throws (drives the parent shutdown catch arm)
@@ -75,6 +79,13 @@ class MockMinimalDapClient extends EventEmitter {
     if (command === 'attach' && MockMinimalDapClient.emitInitializedAfterAttach) {
       setTimeout(() => this.emit('event', { event: 'initialized' }), 5);
     }
+    if (MockMinimalDapClient.emitInitializedSyncOn.has(command)) {
+      // Same-chunk semantics (issue #529): the real client dispatches an event
+      // that shares a socket chunk with the response synchronously, while the
+      // response's awaiter is still parked in the microtask queue — so a
+      // listener registered after `await sendRequest(...)` never sees it.
+      this.emit('event', { event: 'initialized' });
+    }
 
     // Simulate responses
     if (command === 'initialize') {
@@ -141,6 +152,7 @@ describe('ChildSessionManager', () => {
     MockMinimalDapClient.setBreakpointsResponses = [];
     MockMinimalDapClient.emitStoppedAfterAttach = false;
     MockMinimalDapClient.emitInitializedAfterAttach = false;
+    MockMinimalDapClient.emitInitializedSyncOn.clear();
     MockMinimalDapClient.threadsResponse = undefined;
     MockMinimalDapClient.shutdownThrows = false;
   });
@@ -193,6 +205,69 @@ describe('ChildSessionManager', () => {
       }
     });
 
+    it('does not stall adoption when the post-attach initialized rides the attach response (issue #529)', async () => {
+      // The post-attach 'initialized' is emitted synchronously during the
+      // attach request — before handlePostAttachInit could register a
+      // listener. Without the latch, its 3s waitForEvent times out in full,
+      // delaying the CDP bridge attach past the entry pause.
+      vi.useFakeTimers();
+      try {
+        MockMinimalDapClient.emitInitializedSyncOn.add('attach');
+        MockMinimalDapClient.emitStoppedAfterAttach = true;
+
+        const createPromise = manager.createChildSession({
+          pendingId: 'test-pending-race',
+          host: 'localhost',
+          port: 9229,
+          parentConfig: { type: 'pwa-node', request: 'launch' }
+        });
+        let resolved = false;
+        void createPromise.then(() => { resolved = true; }, () => { resolved = true; });
+
+        // Well under the 3s post-attach wait: adoption must already be done.
+        await vi.advanceTimersByTimeAsync(1000);
+        expect(resolved).toBe(true);
+        await createPromise;
+
+        // sawPostInit=true also gates the post-attach mirror re-send: a
+        // second setExceptionBreakpoints proves the latch was consumed
+        // rather than the wait timing out to false.
+        const child = MockMinimalDapClient.instances[0];
+        const exceptionRequests = child.requests.filter(r => r.command === 'setExceptionBreakpoints');
+        expect(exceptionRequests.length).toBeGreaterThanOrEqual(2);
+      } finally {
+        vi.useRealTimers();
+      }
+    });
+
+    it('does not stall adoption when initialized rides the initialize response (issue #529)', async () => {
+      vi.useFakeTimers();
+      try {
+        MockMinimalDapClient.suppressInitialized = true;
+        MockMinimalDapClient.emitInitializedSyncOn.add('initialize');
+        MockMinimalDapClient.emitStoppedAfterAttach = true;
+
+        const createPromise = manager.createChildSession({
+          pendingId: 'test-pending-race-init',
+          host: 'localhost',
+          port: 9229,
+          parentConfig: { type: 'pwa-node', request: 'launch' }
+        });
+        let resolved = false;
+        void createPromise.then(() => { resolved = true; }, () => { resolved = true; });
+
+        // Well under initializeChild's 12s wait (and the 3s post-attach one).
+        // The post-attach wait sees no second 'initialized' and legitimately
+        // times out at 3s — advance past it, but nowhere near 12s.
+        await vi.advanceTimersByTimeAsync(4000);
+        expect(resolved).toBe(true);
+        await createPromise;
+        expect(manager.hasActiveChildren()).toBe(true);
+      } finally {
+        vi.useRealTimers();
+      }
+    });
+
     it('sends resolved exception filters to the child when a break mode is set (issue #220)', async () => {
       vi.useFakeTimers();
       try {