diff --git a/src/browser/CdpObservationSession.ts b/src/browser/CdpObservationSession.ts
index 694d2cd8c7..b256c4fa4f 100644
--- a/src/browser/CdpObservationSession.ts
+++ b/src/browser/CdpObservationSession.ts
@@ -106,6 +106,7 @@ export const observeCdpSession = async (
       message: "Browser observation window ended",
       terminal: true,
     });
+    if (capture.scopeExcluded) endReason = "target_left_scope";
     return {
       browser: context.discovery.version,
       target: {
@@ -139,6 +140,7 @@ class TimelineCapture {
   finalUrl: string | null;
   #sequence = 0;
   #pendingReload = false;
+  #scopeExcluded = false;
   #endReason: EndReason | undefined;
   readonly #listeners = new Set<(reason: EndReason) => void>();
 
@@ -152,7 +154,7 @@ class TimelineCapture {
   }
 
   ingest(event: CdpEvent): void {
-    if (this.#endReason !== undefined) return;
+    if (this.#endReason !== undefined || this.#scopeExcluded) return;
     const params = recordValue(event.params);
     if (params === undefined) return;
     switch (event.method) {
@@ -207,10 +209,24 @@ class TimelineCapture {
   }
 
   setFinalUrl(rawUrl: string): void {
+    if (this.#scopeExcluded) return;
     const destination = scopedUrl(rawUrl, this.allowedOrigins);
     this.finalUrl = destination.scope === "approved" ? destination.url : null;
   }
 
+  get scopeExcluded(): boolean {
+    return this.#scopeExcluded;
+  }
+
+  excludeTargetScope(
+    reason: "invalid_protocol_value" | "out_of_target_scope",
+  ): void {
+    if (this.#scopeExcluded) return;
+    this.#scopeExcluded = true;
+    this.finalUrl = null;
+    this.completeness.exclude("timeline", reason);
+  }
+
   #navigationRequested(event: CdpEvent, params: UnknownRecord): void {
     if (!isMainFrameNavigation(event, this.mainFrameId)) return;
     const reason = safeDetail(params.reason);
@@ -239,8 +255,7 @@ class TimelineCapture {
     this.#pendingReload = false;
     if (destination.scope === "approved") this.finalUrl = destination.url;
     else {
-      this.finalUrl = null;
-      this.completeness.exclude("timeline", "out_of_target_scope");
+      this.excludeTargetScope("out_of_target_scope");
       this.end("target_left_scope");
     }
   }
@@ -258,8 +273,7 @@ class TimelineCapture {
     });
     if (destination.scope === "approved") this.finalUrl = destination.url;
     else {
-      this.finalUrl = null;
-      this.completeness.exclude("timeline", "out_of_target_scope");
+      this.excludeTargetScope("out_of_target_scope");
       this.end("target_left_scope");
     }
   }
@@ -283,7 +297,7 @@ class TimelineCapture {
       detail: null,
     });
     if (destination.scope !== "approved") {
-      this.completeness.exclude("timeline", "out_of_target_scope");
+      this.excludeTargetScope("out_of_target_scope");
       this.end("target_left_scope");
     }
   }
@@ -370,12 +384,14 @@ const captureFinalUrl = async (
   capture: TimelineCapture,
   allowedOrigins: ReadonlySet<string>,
 ): Promise<EndReason> => {
+  if (capture.scopeExcluded) return "target_left_scope";
   const result = await context.connection.send(
     "Page.getFrameTree",
     {},
     context.sessionId,
     context.signal,
   );
+  if (capture.scopeExcluded) return "target_left_scope";
   const url = mainFrameUrl(result);
   if (
     url !== undefined &&
@@ -384,9 +400,7 @@ const captureFinalUrl = async (
     capture.setFinalUrl(url);
     return "window_elapsed";
   }
-  capture.finalUrl = null;
-  capture.completeness.exclude(
-    "timeline",
+  capture.excludeTargetScope(
     url === undefined ? "invalid_protocol_value" : "out_of_target_scope",
   );
   return "target_left_scope";
diff --git a/tests/boundary/browser/cdpObservationResourceTypes.test.ts b/tests/boundary/browser/cdpObservationResourceTypes.test.ts
index f7c97d3ddc..2dece6f965 100644
--- a/tests/boundary/browser/cdpObservationResourceTypes.test.ts
+++ b/tests/boundary/browser/cdpObservationResourceTypes.test.ts
@@ -50,8 +50,80 @@ it.each(["Document", undefined] as const)(
     );
     if (!result.ok) throw result.error;
     expect(result.value.window.end_reason).toBe("target_left_scope");
+    expect(result.value.target.final_url).toBeNull();
     expect(result.value.timeline.some(({ type }) => type === "redirect")).toBe(
       true,
     );
   },
 );
+
+it("keeps final URL unknown when a redirect races the final frame-tree read", async () => {
+  let frameTreeReads = 0;
+  const browser = await startFakeCdpBrowser({
+    eventsBeforeReply: ["Page.getFrameTree"],
+    commandEvents: (command) => {
+      if (command.method !== "Page.getFrameTree") return undefined;
+      frameTreeReads += 1;
+      if (frameTreeReads !== 2 || command.sessionId === undefined)
+        return undefined;
+      return [
+        {
+          method: "Network.requestWillBeSent",
+          sessionId: command.sessionId,
+          params: {
+            requestId: "late-main-document",
+            type: "Document",
+            frameId: "frame-main",
+            request: {
+              url: "https://private.example.test/redirected",
+              method: "GET",
+            },
+            redirectResponse: { status: 302 },
+          },
+        },
+      ];
+    },
+  });
+  onTestFinished(async () => {
+    await browser.close();
+  });
+  const result = await new CdpBrowserProvider().observeSession(
+    observeWebSessionInputSchema.parse({
+      cdp_endpoint: browser.endpoint,
+      allowed_origins: [browser.allowedOrigin],
+      target_id: "allowed-page",
+      observation_ms: 1,
+    }),
+  );
+
+  if (!result.ok) throw result.error;
+  expect(result.value.window.end_reason).toBe("target_left_scope");
+  expect(result.value.target.final_url).toBeNull();
+  expect(result.value.timeline.at(-1)).toMatchObject({
+    type: "redirect",
+    url: null,
+    destination_scope: "outside_policy",
+  });
+  expect(JSON.stringify(result.value)).not.toContain("private.example.test");
+});
+
+it("retains the approved URL returned by the final frame-tree read", async () => {
+  const browser = await startFakeCdpBrowser();
+  onTestFinished(async () => {
+    await browser.close();
+  });
+  const result = await new CdpBrowserProvider().observeSession(
+    observeWebSessionInputSchema.parse({
+      cdp_endpoint: browser.endpoint,
+      allowed_origins: [browser.allowedOrigin],
+      target_id: "allowed-page",
+      observation_ms: 1,
+    }),
+  );
+
+  if (!result.ok) throw result.error;
+  expect(result.value.window.end_reason).toBe("window_elapsed");
+  expect(result.value.target.final_url).toBe(
+    `${browser.allowedOrigin}/app?token=frame-secret`,
+  );
+});