fix(browser): preserve uncertain main-frame navigation identity

Own CDP frame applicability and identity at the parsed event boundary. Preserve malformed or incomplete main-frame facts, recognize replacement roots, and carry the same document identity through captures, screenshots, timelines, and execution windows.

Validation: full check:ci and docs:check; 763 browser and dispatch tests passed, 6 skipped. Independent source and fixture-lifecycle review passed. Local real-Chrome behavior was not exercised.

Closes #5665

src/browser/execution/CdpExecutionWindow.test.ts

@@ -63,3 +63,57 @@ it("settles caller cancellation and removes its local timer", async () => {
     vi.useRealTimers();
   }
 });
+
+it("keeps a root document transition distinct from a child frame event", async () => {
+  const root = new CdpExecutionWindow({
+    target: { frame_id: "selected-main" },
+    operation: "observe_web_execution",
+    options: {},
+  });
+  const rootResult = root.start(30_000);
+  root.ingest({
+    method: "Page.frameNavigated",
+    params: { frame: { id: "new-main", url: "https://example.test/" } },
+  });
+  await expect(rootResult).resolves.toBe("document_changed");
+
+  const child = new CdpExecutionWindow({
+    target: { frame_id: "selected-main" },
+    operation: "observe_web_execution",
+    options: {},
+  });
+  const childResult = child.start(30_000);
+  child.ingest({
+    method: "Page.frameNavigated",
+    params: {
+      frame: {
+        id: "child-frame",
+        parentId: "selected-main",
+        url: "https://example.test/child",
+      },
+    },
+  });
+  expect(child.active).toBe(true);
+  child.end("window_elapsed");
+  await expect(childResult).resolves.toBe("window_elapsed");
+});
+
+it("surfaces malformed frame identity as a protocol failure without guessing a transition", async () => {
+  const window = new CdpExecutionWindow({
+    target: { frame_id: "selected-main" },
+    operation: "observe_web_execution",
+    options: {},
+  });
+  const result = window.start(30_000);
+  window.ingest({
+    method: "Page.frameNavigated",
+    params: {
+      frame: { id: "child-frame", parentId: 7, url: "https://example.test/" },
+    },
+  });
+  await expect(result).rejects.toMatchObject({
+    _tag: "BrowserObservationError",
+    reason: "protocol_error",
+  });
+  expect(window.reason).toBeUndefined();
+});

src/browser/execution/CdpExecutionWindow.ts

@@ -3,6 +3,8 @@ import type { AnalysisError } from "../../domain/analysisErrorBase.js";
 import type { WebExecution } from "../../domain/webExecution.js";
 import type { CdpEvent } from "../CdpConnection.js";
 import type { CdpRuntimeSession } from "./CdpRuntimeSession.js";
+import { BrowserObservationError } from "../../domain/browserObservationError.js";
+import { cdpFrameIdentity } from "../CdpCaptureEventHelpers.js";
 
 type EndReason = WebExecution["window"]["end_reason"];
 /** One finite document-scoped window, with an actual armed point and event-driven termination. */
@@ -33,15 +35,30 @@ export class CdpExecutionWindow {
     if (!this.active) return;
     if (event.method === "Runtime.executionContextsCleared")
       this.end("document_changed");
-    if (
-      event.method === "Page.frameNavigated" &&
-      typeof event.params === "object" &&
-      event.params !== null &&
-      "frame" in event.params
-    ) {
-      const frame = event.params.frame;
-      if (typeof frame === "object" && frame !== null && !("parentId" in frame))
+    if (event.method === "Page.frameNavigated") {
+      const identity = cdpFrameIdentity(event, this.session.target.frame_id);
+      if (identity.identityIssue !== null || identity.parentIssue !== null) {
+        this.fail(
+          new BrowserObservationError(this.session.operation, "protocol_error"),
+        );
+        return;
+      }
+      if (identity.selection === "main") {
         this.end("document_changed");
+        return;
+      }
+      if (identity.parentRelation === "child") return;
+      if (
+        identity.selection === "other" &&
+        identity.parentRelation === "root"
+      ) {
+        this.end("document_changed");
+        return;
+      }
+      this.fail(
+        new BrowserObservationError(this.session.operation, "protocol_error"),
+      );
+      return;
     }
     if (
       event.method === "Page.frameDetached" &&