fix(sandbox): reset step store for long-lived bridge work

A run-time `sandbox.exec` span attached to a dead startup step. Two bridge
startup steps start long-lived work inside their measured step body: a poll
timer, socket handlers, and a callback-bridge worker loop. Node snapshots the
active-step store on each async resource at creation time, so this work kept
the ended step store. Each later run-time exec then read that store and opened
its span under the ended step, and it copied a wrong `criticalPath: false` flag.

Add an exported `runWithoutActiveStep` helper in startup-timing and wrap the
long-lived poll timer, the socket handlers, and the callback-bridge worker loop
of both bridge lanes. Each continuation now reads an empty store, so each
run-time exec opens an unparented span with no stale `criticalPath` flag.
Control flow is unchanged and the change adds no new dependency.

Co-authored-by: Paperclip <noreply@paperclip.ing>

packages/adapter-utils/src/acpx-engine/startup-timing.test.ts

@@ -7,6 +7,7 @@ import {
   getActiveStepContext,
   measureStartupStep,
   normalizeProviderFamily,
+  runWithoutActiveStep,
   SANDBOX_STARTUP_SPAN_ATTR_PREFIX,
   SANDBOX_STARTUP_SPAN_ATTRS,
   setSandboxRootSpanAttributes,
@@ -495,6 +496,86 @@ describe("getActiveStepContext", () => {
     }, { criticalPath: false });
     expect(seen!.criticalPath).toBe(false);
   });
+
+  it("keeps the ended step store in a timer scheduled inside the step body", async () => {
+    // Node snapshots the active store on each async resource at creation time.
+    // A timer scheduled inside a measured step body keeps that step store, even
+    // after the step span ends. A later run-time exec then reads the ended step
+    // and parents its `sandbox.exec` span to a dead startup step. This test locks
+    // that leak, so the fix and its guard test stay honest.
+    let storeInTimer: ReturnType<typeof getActiveStepContext> = null;
+    let fireTimer!: () => void;
+    const timerRan = new Promise<void>((resolve) => {
+      fireTimer = resolve;
+    });
+
+    await measureStartupStep(
+      { onEvent: vi.fn(async () => {}) },
+      () => 0,
+      "bridge.process-session",
+      async () => {
+        setTimeout(() => {
+          storeInTimer = getActiveStepContext();
+          fireTimer();
+        }, 0);
+        return "started";
+      },
+      { criticalPath: false },
+    );
+
+    // The step span already ended, so the main line reads no active step.
+    expect(getActiveStepContext()).toBeNull();
+
+    await timerRan;
+
+    // Yet the timer callback still reads the ended step context. This is the
+    // store leak the bridge boundary fix removes.
+    expect(storeInTimer).not.toBeNull();
+    expect(storeInTimer!.criticalPath).toBe(false);
+  });
+
+  it("clears the active step for a continuation wrapped in runWithoutActiveStep", async () => {
+    // The bridge boundary wraps its long-lived poll timer in `runWithoutActiveStep`.
+    // A timer scheduled inside that empty store scope reads no active step, so a
+    // later run-time exec opens an unparented span instead of one under the ended
+    // startup step.
+    let storeInTimer: ReturnType<typeof getActiveStepContext> = null;
+    let sawTimer = false;
+    let fireTimer!: () => void;
+    const timerRan = new Promise<void>((resolve) => {
+      fireTimer = resolve;
+    });
+
+    await measureStartupStep(
+      { onEvent: vi.fn(async () => {}) },
+      () => 0,
+      "bridge.process-session",
+      async () => {
+        runWithoutActiveStep(() => {
+          setTimeout(() => {
+            storeInTimer = getActiveStepContext();
+            sawTimer = true;
+            fireTimer();
+          }, 0);
+        });
+        return "started";
+      },
+      { criticalPath: false },
+    );
+
+    await timerRan;
+
+    expect(sawTimer).toBe(true);
+    expect(storeInTimer).toBeNull();
+  });
+
+  it("returns the work result and restores the previous active step", async () => {
+    // Outside any measured step the previous store is empty, so the helper both
+    // returns the work value and leaves the store empty afterward.
+    const value = runWithoutActiveStep(() => "value");
+    expect(value).toBe("value");
+    expect(getActiveStepContext()).toBeNull();
+  });
 });
 
 describe("clampSpanLabel", () => {

packages/adapter-utils/src/acpx-engine/startup-timing.ts

@@ -332,7 +332,7 @@ export interface ActiveStepContext {
  * a module-level singleton, so the value propagates across `await` boundaries
  * and across package boundaries that share this module.
  */
-const activeStepContextStorage = new AsyncLocalStorage<ActiveStepContext>();
+const activeStepContextStorage = new AsyncLocalStorage<ActiveStepContext | undefined>();
 
 /**
  * Return the active step context, or `null` when no measured step is running.
@@ -344,6 +344,26 @@ export function getActiveStepContext(): ActiveStepContext | null {
   return activeStepContextStorage.getStore() ?? null;
 }
 
+/**
+ * Run `work` with no active step context, then restore the previous store. A
+ * bridge boundary uses this to start its long-lived poll timer and socket
+ * handlers outside the measured step store.
+ *
+ * Node snapshots the active store on each async resource at creation time. So a
+ * timer or a handler scheduled inside a measured step body keeps that step store
+ * after the step span ends. A later run-time exec then reads the ended step and
+ * parents its `sandbox.exec` span to a dead startup step, and it copies the
+ * step's `criticalPath` flag. This helper resets the store for the wrapped work,
+ * so each continuation reads an empty store. Each run-time exec then opens an
+ * unparented span with no stale `criticalPath` flag.
+ *
+ * The helper forwards only the opaque store, so this package stays free of
+ * `@opentelemetry/api`. It needs no Node version gate.
+ */
+export function runWithoutActiveStep<T>(work: () => T): T {
+  return activeStepContextStorage.run(undefined, work);
+}
+
 /**
  * Set a numeric span attribute only when the value is a finite number. A reader
  * that returns `undefined` (the counter is unavailable) yields no attribute,

packages/adapter-utils/src/execution-target.ts

@@ -46,6 +46,7 @@ import {
 } from "./server-utils.js";
 import { sanitizeRemoteExecutionEnv } from "./remote-execution-env.js";
 import { preferredShellForSandbox, shellCommandArgs } from "./sandbox-shell.js";
+import { runWithoutActiveStep } from "./acpx-engine/startup-timing.js";
 import type { RuntimeProgressSink, RuntimeStatusSink } from "./runtime-progress.js";
 import type { LocalProcessSandboxOptions } from "./local-process-sandbox.js";
 
@@ -1488,7 +1489,10 @@ export async function startAdapterExecutionTargetProcessSessionBridge(input: {
   };
 
   const liveSockets = new Set<net.Socket>();
-  const server = net.createServer((nextSocket) => {
+  // Register the per-connection socket handlers outside the measured bridge step
+  // store. A stdin write from a socket handler is a run-time exec, not startup
+  // work, so its `sandbox.exec` span must not parent to the ended bridge step.
+  const server = net.createServer((nextSocket) => runWithoutActiveStep(() => {
     liveSockets.add(nextSocket);
     nextSocket.setEncoding("utf8");
     nextSocket.on("error", () => undefined);
@@ -1547,7 +1551,7 @@ export async function startAdapterExecutionTargetProcessSessionBridge(input: {
         });
       }
     });
-  });
+  }));
 
   const poll = async () => {
     if (stopping) return;
@@ -1572,16 +1576,24 @@ export async function startAdapterExecutionTargetProcessSessionBridge(input: {
       return;
     } finally {
       if (!stopping) {
-        pollTimer = setTimeout(() => void poll(), 100);
-        pollTimer.unref?.();
+        schedulePoll();
       }
     }
   };
 
+  // Schedule the long-lived poll timer outside the measured bridge step store.
+  // The poll loop reads remote event files with run-time execs, not startup
+  // work, so a poll `sandbox.exec` span must not parent to the ended bridge step.
+  // `runWithoutActiveStep` also empties the store for the re-arm timer that the
+  // poll body schedules, so every later tick stays unparented too.
+  const schedulePoll = () => {
+    pollTimer = setTimeout(() => runWithoutActiveStep(() => void poll()), 100);
+    pollTimer.unref?.();
+  };
+
   const port = await waitForLocalServerListen(server);
   const agentCommand = await writeProcessSessionProxyScript(proxyDir, port, token);
-  pollTimer = setTimeout(() => void poll(), 100);
-  pollTimer.unref?.();
+  schedulePoll();
 
   return {
     agentCommand,
@@ -1787,7 +1799,13 @@ export async function startAdapterExecutionTargetPaperclipBridge(input: {
     // this flag is enabled. Only intended for active debugging in trusted
     // environments.
     const bridgeDebugEnabled = isBridgeDebugEnabled(process.env);
-    worker = await startSandboxCallbackBridgeWorker({
+    // Start the long-lived callback-bridge worker loop outside the measured
+    // bridge step store. The loop reads and writes queue files with run-time
+    // execs for the whole run, not startup work, so a worker `sandbox.exec` span
+    // must not parent to the ended `bridge.paperclip` step or copy its
+    // `criticalPath` flag. `runWithoutActiveStep` empties the store for the loop
+    // that the worker start schedules, so every later poll tick stays unparented.
+    worker = await runWithoutActiveStep(() => startSandboxCallbackBridgeWorker({
       client,
       queueDir,
       maxBodyBytes,
@@ -1824,7 +1842,7 @@ export async function startAdapterExecutionTargetPaperclipBridge(input: {
           body: await readBridgeForwardResponseBody(response, maxBodyBytes),
         };
       },
-    });
+    }));
     server = await startSandboxCallbackBridgeServer({
       runner,
       remoteCwd: target.remoteCwd,