diff --git a/src/browser/CdpObservationSession.ts b/src/browser/CdpObservationSession.ts
index 74f457cc4c..1680acf1dd 100644
--- a/src/browser/CdpObservationSession.ts
+++ b/src/browser/CdpObservationSession.ts
@@ -144,6 +144,8 @@ export const observeCdpSession = async (
       message: "Browser observation window ended",
       terminal: true,
     });
+    // Terminal progress is awaited and may admit more protocol events.
+    capture.assertRequestOwnershipWithinLimit();
     if (capture.scopeExcluded) endReason = "target_left_scope";
     return {
       browser: context.discovery.version,
diff --git a/tests/boundary/browser/cdpSessionRequestBudget.test.ts b/tests/boundary/browser/cdpSessionRequestBudget.test.ts
index bdeae17e8a..b469fd8639 100644
--- a/tests/boundary/browser/cdpSessionRequestBudget.test.ts
+++ b/tests/boundary/browser/cdpSessionRequestBudget.test.ts
@@ -1,4 +1,5 @@
 import { expect, it, onTestFinished, vi } from "vitest";
+import { CdpConnection } from "../../../src/browser/CdpConnection.js";
 import { CdpBrowserProvider } from "../../../src/browser/CdpBrowserProvider.js";
 import { observeWebSessionInputSchema } from "../../../src/domain/browserSession.js";
 import { startFakeCdpBrowser } from "../../fixtures/fakeCdpBrowser.js";
@@ -17,53 +18,73 @@ vi.mock("../../../src/domain/webRuntime.js", async (importOriginal) => {
   };
 });
 
-it("refuses active document identity retention before reporting a complete session", async () => {
-  const browser = await startFakeCdpBrowser({ commandEvents: () => [] });
-  const provider = new CdpBrowserProvider();
-  onTestFinished(async () => {
-    await provider.close();
-    await browser.close();
-  });
-  const result = await provider.observeSession(
-    observeWebSessionInputSchema.parse({
-      cdp_endpoint: browser.endpoint,
-      target_id: "allowed-page",
-      allowed_origins: [browser.allowedOrigin],
-      observation_ms: 1_000,
-    }),
-    {
-      signal: AbortSignal.timeout(2_000),
-      progress: {
-        report: async (update) => {
-          if (update.completed === 1)
-            browser.emitEvent({
-              method: "Network.requestWillBeSent",
-              sessionId: "session-1",
-              params: {
-                requestId: "r".repeat(128),
-                type: "Document",
-                frameId: "frame-main",
-                loaderId: "loader",
-                timestamp: 100,
-                request: {
-                  url: `${browser.allowedOrigin}/page`,
-                  method: "GET",
+it.each([1, 2])(
+  "refuses active document identity retention at progress stage %s before reporting a complete session",
+  async (stage) => {
+    let received: () => void = () => {};
+    const delivered = new Promise<void>((resolve) => {
+      received = resolve;
+    });
+    const onEvent = CdpConnection.prototype.onEvent;
+    const delivery = vi
+      .spyOn(CdpConnection.prototype, "onEvent")
+      .mockImplementation(function (this: CdpConnection, listener) {
+        return onEvent.call(this, (event) => {
+          listener(event);
+          if (event.method === "Network.requestWillBeSent") received();
+        });
+      });
+    const browser = await startFakeCdpBrowser({ commandEvents: () => [] });
+    const provider = new CdpBrowserProvider();
+    onTestFinished(async () => {
+      delivery.mockRestore();
+      await provider.close();
+      await browser.close();
+    });
+    const result = await provider.observeSession(
+      observeWebSessionInputSchema.parse({
+        cdp_endpoint: browser.endpoint,
+        target_id: "allowed-page",
+        allowed_origins: [browser.allowedOrigin],
+        observation_ms: 5,
+      }),
+      {
+        signal: AbortSignal.timeout(2_000),
+        progress: {
+          report: async (update) => {
+            if (update.completed === stage) {
+              browser.emitEvent({
+                method: "Network.requestWillBeSent",
+                sessionId: "session-1",
+                params: {
+                  requestId: "r".repeat(128),
+                  type: "Document",
+                  frameId: "frame-main",
+                  loaderId: "loader",
+                  timestamp: 100,
+                  request: {
+                    url: `${browser.allowedOrigin}/page`,
+                    method: "GET",
+                  },
                 },
-              },
-            });
+              });
+              // Observe actual parser/listener delivery before final progress resolves.
+              await delivered;
+            }
+          },
         },
       },
-    },
-  );
-  expect(result).toMatchObject({
-    ok: false,
-    error: {
-      _tag: "BrowserObservationError",
-      reason: "payload_limit",
-      detail: expect.stringContaining("Active document request identities"),
-    },
-  });
-  expect(browser.commands.map(({ method }) => method)).toContain(
-    "Target.detachFromTarget",
-  );
-});
+    );
+    expect(result).toMatchObject({
+      ok: false,
+      error: {
+        _tag: "BrowserObservationError",
+        reason: "payload_limit",
+        detail: expect.stringContaining("Active document request identities"),
+      },
+    });
+    expect(browser.commands.map(({ method }) => method)).toContain(
+      "Target.detachFromTarget",
+    );
+  },
+);