fix(geometry): preserve OOPIF scale with occupied scrollbars

apps/extension/src/tools/__tests__/file-transfer.test.ts

@@ -436,6 +436,8 @@ describe("file transfer tools", () => {
         if (method === "DOM.getContentQuads") {
           return { quads: [[10, 20, 210, 20, 210, 120, 10, 120]] };
         }
+        if (method === "Runtime.evaluate")
+          return { result: { value: { width: 400, height: 300 } } };
         if (method === "Page.getLayoutMetrics") {
           return { cssLayoutViewport: { clientWidth: 400, clientHeight: 300 } };
         }

apps/extension/src/tools/__tests__/frame-geometry.test.ts

@@ -13,7 +13,138 @@ import {
 import { GeometryContext } from "../geometry/frame-context";
 import type { CdpRunner } from "../shared";
 
+function scrollbarDriver(
+  visible = { width: 185, height: 89 },
+  frameSize: unknown = { width: 200, height: 100 },
+) {
+  const send = vi.fn(async (target: { sessionId?: string }, method: string) => {
+    if (method === "Runtime.evaluate") return { result: { value: frameSize } };
+    if (method === "Page.getLayoutMetrics")
+      return {
+        cssLayoutViewport: {
+          clientWidth: target.sessionId ? visible.width : 800,
+          clientHeight: target.sessionId ? visible.height : 600,
+        },
+      };
+    if (method === "DOM.getBoxModel")
+      return {
+        model: {
+          content: target.sessionId
+            ? [0, 0, 200, 0, 200, 100, 0, 100]
+            : [100, 100, 500, 100, 500, 300, 100, 300],
+        },
+      };
+    if (method === "DOM.getContentQuads")
+      return { quads: [[180, 80, 230, 80, 230, 120, 180, 120]] };
+    throw new Error(`unexpected ${method}`);
+  });
+  const cdp: CdpRunner = {
+    send: (tabId, method) => send({ tabId } as never, method) as never,
+    sendToTarget: send as CdpRunner["sendToTarget"],
+    getFrameGraph: async () => ({
+      rootFrameId: "main",
+      frames: [
+        { frameId: "main", target: { tabId: 4 } },
+        {
+          frameId: "child",
+          parentFrameId: "main",
+          ownerBackendNodeId: 10,
+          target: { tabId: 4, sessionId: "child" },
+        },
+        {
+          frameId: "same-child",
+          parentFrameId: "child",
+          ownerBackendNodeId: 20,
+          target: { tabId: 4, sessionId: "child" },
+        },
+      ],
+    }),
+  };
+  return { cdp, send };
+}
+
 describe("frame geometry projection", () => {
+  it.each([
+    { width: 200, height: 100 },
+    { width: 185, height: 100 },
+    { width: 200, height: 89 },
+    { width: 185, height: 89 },
+  ])("preserves scale and clips scrollbar strips for visible viewport $width × $height", async (visible) => {
+    const { cdp, send } = scrollbarDriver(visible);
+    const geometry = await resolveNodeGeometry(cdp, 4, {
+      target: { tabId: 4, sessionId: "child" },
+      frameId: "child",
+      backendNodeId: 101,
+    });
+    expect(geometry).toMatchObject({
+      topBounds: {
+        x: 460,
+        y: 260,
+        width: (visible.width - 180) * 2,
+        height: (visible.height - 80) * 2,
+      },
+      actionPoint: { x: 460 + visible.width - 180, y: 260 + visible.height - 80 },
+      targetActionPoint: { x: (180 + visible.width) / 2, y: (80 + visible.height) / 2 },
+    });
+    expect(send.mock.calls.filter(([, method]) => method === "Runtime.evaluate")).toHaveLength(1);
+    expect(send.mock.calls.filter(([, method]) => method === "Page.getLayoutMetrics")).toHaveLength(
+      2,
+    );
+  });
+
+  it("shares the full viewport read across same-target frames, and refreshes it next operation", async () => {
+    const { cdp, send } = scrollbarDriver();
+    const context = new GeometryContext(cdp, 4);
+    await Promise.all([context.targetProjection("child"), context.targetProjection("same-child")]);
+    expect(send.mock.calls.filter(([, method]) => method === "Runtime.evaluate")).toHaveLength(1);
+    await new GeometryContext(cdp, 4).targetProjection("child");
+    expect(send.mock.calls.filter(([, method]) => method === "Runtime.evaluate")).toHaveLength(2);
+  });
+
+  it.each([
+    null,
+    {},
+    { width: 0, height: 100 },
+    { width: 200, height: NaN },
+  ])("rejects unavailable full viewport dimensions: %j", async (size) => {
+    const { cdp } = scrollbarDriver(undefined, size);
+    expect(await new GeometryContext(cdp, 4).targetProjection("child")).toBeNull();
+  });
+
+  it("clips an inner OOPIF against an intermediate OOPIF's occupied scrollbar strips", async () => {
+    const { cdp } = scrollbarDriver();
+    const outer = cdp.sendToTarget!;
+    cdp.sendToTarget = async (target, method, params) => {
+      if (method === "DOM.getBoxModel")
+        return { model: { content: [150, 60, 250, 60, 250, 120, 150, 120] } } as never;
+      if (target.sessionId !== "inner") return outer(target, method, params);
+      if (method === "Runtime.evaluate")
+        return { result: { value: { width: 100, height: 60 } } } as never;
+      if (method === "Page.getLayoutMetrics")
+        return { cssLayoutViewport: { clientWidth: 90, clientHeight: 50 } } as never;
+      if (method === "DOM.getContentQuads")
+        return { quads: [[0, 0, 100, 0, 100, 60, 0, 60]] } as never;
+      throw new Error(`unexpected ${method}`);
+    };
+    const graph = await cdp.getFrameGraph!(4);
+    graph.frames[2] = {
+      frameId: "inner",
+      parentFrameId: "child",
+      ownerBackendNodeId: 20,
+      target: { tabId: 4, sessionId: "inner" },
+    };
+    cdp.getFrameGraph = async () => graph;
+    expect(
+      await resolveNodeGeometry(cdp, 4, {
+        target: { tabId: 4, sessionId: "inner" },
+        frameId: "inner",
+        backendNodeId: 101,
+      }),
+    ).toMatchObject({
+      topBounds: { x: 400, y: 220, width: 70, height: 58 },
+    });
+  });
+
   it("keeps region bounds separate from polygon area", () => {
     const region = [
       rectPolygon({ x: 0, y: 0, w: 10, h: 10 }),
@@ -77,6 +208,8 @@ describe("frame geometry projection", () => {
     const cdp: CdpRunner = {
       send: send as CdpRunner["send"],
       sendToTarget: vi.fn(async (_target, method) => {
+        if (method === "Runtime.evaluate")
+          return { result: { value: { width: 200, height: 100 } } };
         if (method === "Page.getLayoutMetrics") {
           return { cssLayoutViewport: { clientWidth: 200, clientHeight: 100 } };
         }
@@ -135,6 +268,8 @@ describe("frame geometry projection", () => {
         throw new Error(`unexpected root command ${method}`);
       }) as CdpRunner["send"],
       sendToTarget: vi.fn(async (_target, method) => {
+        if (method === "Runtime.evaluate")
+          return { result: { value: { width: 200, height: 100 } } };
         if (method === "Page.getLayoutMetrics") {
           return { cssLayoutViewport: { clientWidth: 200, clientHeight: 100 } };
         }
@@ -196,6 +331,8 @@ describe("frame geometry projection", () => {
       }) as CdpRunner["send"],
       sendToTarget: vi.fn(async (_target, method) => {
         if (method === "DOM.scrollIntoViewIfNeeded") return {};
+        if (method === "Runtime.evaluate")
+          return { result: { value: { width: 200, height: 100 } } };
         if (method === "Page.getLayoutMetrics") {
           return { cssLayoutViewport: { clientWidth: 200, clientHeight: 100 } };
         }

apps/extension/src/tools/__tests__/human-loop.test.ts

@@ -433,6 +433,7 @@ describe("handleRequestHelp", () => {
       if (method === "DOM.getContentQuads") {
         return { quads: [[10, 20, 110, 20, 110, 60, 10, 60]] };
       }
+      if (method === "Runtime.evaluate") return { result: { value: { width: 200, height: 100 } } };
       if (method === "Page.getLayoutMetrics") {
         return { cssLayoutViewport: { clientWidth: 200, clientHeight: 100 } };
       }

apps/extension/src/tools/__tests__/interaction.test.ts

@@ -201,6 +201,7 @@ describe("handleClick", () => {
       if (method === "DOM.getContentQuads") {
         return { quads: [[10, 20, 110, 20, 110, 60, 10, 60]] };
       }
+      if (method === "Runtime.evaluate") return { result: { value: { width: 200, height: 100 } } };
       if (method === "Page.getLayoutMetrics") {
         return { cssLayoutViewport: { clientWidth: 200, clientHeight: 100 } };
       }
@@ -220,6 +221,7 @@ describe("handleClick", () => {
       { sessionId: "child-session", method: "DOM.scrollIntoViewIfNeeded" },
       { sessionId: "child-session", method: "DOM.getContentQuads" },
       { sessionId: "child-session", method: "Page.getLayoutMetrics" },
+      { sessionId: "child-session", method: "Runtime.evaluate" },
     ]);
     expect(fake.sent.filter((call) => call.method === "Input.dispatchMouseEvent")).toHaveLength(3);
   });

apps/extension/src/tools/__tests__/observation.test.ts

@@ -3380,6 +3380,7 @@ describe("handleSnapshot", () => {
       throw new Error(`unexpected root CDP method ${method}`);
     });
     const sendToTarget = vi.fn(async (_target, method: string) => {
+      if (method === "Runtime.evaluate") return { result: { value: { width: 400, height: 300 } } };
       if (method === "Page.getLayoutMetrics" && ownerGeometry !== "unavailable")
         return {
           visualViewport: { clientWidth: 1000 },

apps/extension/src/tools/__tests__/snapshot-coordinates.browser.test.ts

@@ -1,6 +1,7 @@
 // @vitest-environment node
 import { describe, expect, it } from "vitest";
 import type { CdpFrame, CdpFrameGraph, CdpTarget } from "@/browser-driver/frame-graph";
+import { resolveNodeGeometry } from "../frame-geometry";
 import type { CdpRunner } from "../shared";
 import { captureObservationFacts } from "../vom/capture-coordinator";
 
@@ -11,12 +12,28 @@ type Send = <T = Record<string, unknown>>(
 ) => Promise<T>;
 type Tree = { frame: { id: string; parentId?: string; name?: string }; childFrames?: Tree[] };
 type Rect = { x: number; y: number; w: number; h: number };
-type Oracle = { probe: Rect; owners: Record<string, { x: number; y: number; scale: number }> };
+type Oracle = {
+  probes: Record<string, Rect>;
+  viewport: { width: number; height: number };
+  owners: Record<string, { x: number; y: number; scale: number }>;
+};
+
+function clip(rect: Rect, viewport: Oracle["viewport"]): Rect | null {
+  const x = Math.max(0, rect.x),
+    y = Math.max(0, rect.y);
+  const right = Math.min(viewport.width, rect.x + rect.w);
+  const bottom = Math.min(viewport.height, rect.y + rect.h);
+  return right > x && bottom > y ? { x, y, w: right - x, h: bottom - y } : null;
+}
 
 // The independent oracle uses DOM border boxes and this fixture's axis-aligned
 // iframe transforms. No production snapshot conversion/projection builds expectations.
 const oracleExpression = `(() => {
-  const box = document.querySelector('#probe').getBoundingClientRect();
+  const probes = {};
+  for (const node of document.querySelectorAll('[data-geometry-probe]')) {
+    const box = node.getBoundingClientRect();
+    probes[node.id] = { x: box.x, y: box.y, w: box.width, h: box.height };
+  }
   const owners = {};
   for (const frame of document.querySelectorAll('iframe')) {
     const rect = frame.getBoundingClientRect();
@@ -28,17 +45,31 @@ const oracleExpression = `(() => {
       scale,
     };
   }
-  return { probe: { x: box.x, y: box.y, w: box.width, h: box.height }, owners };
+  return { probes, viewport: { width: document.documentElement.clientWidth, height: document.documentElement.clientHeight }, owners };
 })()`;
 
 describe.skipIf(!process.env.BSK_GEOMETRY_CHROME)("real DOMSnapshot coordinate contract", () => {
-  it.each([
-    { deviceScale: 1, zoom: 1 },
-    { deviceScale: 0.8, zoom: 1 },
-    { deviceScale: 1, zoom: 1.25 },
-    { deviceScale: 2, zoom: 1 },
-    { deviceScale: 2, zoom: 0.8 },
-  ])("matches DOM geometry at device scale $deviceScale and zoom $zoom", async (configuration) => {
+  it.each(
+    [
+      { deviceScale: 1, zoom: 1 },
+      { deviceScale: 0.8, zoom: 1 },
+      { deviceScale: 1, zoom: 1.25 },
+      { deviceScale: 2, zoom: 1 },
+      { deviceScale: 2, zoom: 0.8 },
+    ]
+      .flatMap((configuration) => [
+        { ...configuration, fixture: "snapshot-coordinates", scrollbars: "none" },
+        { ...configuration, fixture: "oopif-scrollbars", scrollbars: "both" },
+      ])
+      .concat(
+        ["vertical", "horizontal", "none"].map((scrollbars) => ({
+          deviceScale: 1,
+          zoom: 1,
+          fixture: "oopif-scrollbars",
+          scrollbars,
+        })),
+      ),
+  )("$fixture: device scale $deviceScale, zoom $zoom, scrollbars $scrollbars", async (configuration) => {
     const evalRoot = new URL("../../../../../evals/browser/", import.meta.url);
     const { createEvalServer } = await import(new URL("lib/server.mjs", evalRoot).href);
     const { withChrome } = await import(
@@ -59,7 +90,9 @@ describe.skipIf(!process.env.BSK_GEOMETRY_CHROME)("real DOMSnapshot coordinate c
           );
           await send(
             "Page.navigate",
-            { url: `${baseUrl}/snapshot-coordinates?run=coordinates` },
+            {
+              url: `${baseUrl}/${configuration.fixture}?run=coordinates&scrollbars=${configuration.scrollbars}`,
+            },
             rootSession,
           );
           await expect
@@ -86,7 +119,7 @@ describe.skipIf(!process.env.BSK_GEOMETRY_CHROME)("real DOMSnapshot coordinate c
             });
             sessions.push(sessionId);
           }
-          expect(sessions.length).toBe(2); // The cross-site fixture must actually be an OOPIF.
+          expect(sessions.length).toBe(configuration.fixture === "oopif-scrollbars" ? 3 : 2);
           const frames: CdpFrame[] = [];
           const names = new Map<string, string>();
           const sessionFor = (target: CdpTarget) => target.sessionId ?? rootSession;
@@ -107,7 +140,7 @@ describe.skipIf(!process.env.BSK_GEOMETRY_CHROME)("real DOMSnapshot coordinate c
             };
             visit(frameTree);
           }
-          expect(frames).toHaveLength(5);
+          expect(frames).toHaveLength(configuration.fixture === "oopif-scrollbars" ? 3 : 5);
           for (const frame of frames) {
             if (!frame.parentFrameId) continue;
             const parent = frames.find((item) => item.frameId === frame.parentFrameId)!;
@@ -127,6 +160,11 @@ describe.skipIf(!process.env.BSK_GEOMETRY_CHROME)("real DOMSnapshot coordinate c
             },
             sendToTarget: (target, method, params) => {
               calls.push(`${target.sessionId ?? target.tabId}:${method}`);
+              if (
+                method === "Runtime.evaluate" &&
+                (params as { expression?: string })?.expression?.includes("window.innerWidth")
+              )
+                calls.push(`${target.sessionId ?? target.tabId}:viewport-size`);
               return send(method, params, sessionFor(target));
             },
             getFrameGraph: async () => graph,
@@ -179,47 +217,130 @@ describe.skipIf(!process.env.BSK_GEOMETRY_CHROME)("real DOMSnapshot coordinate c
             );
             oracles.set(frame.frameId, reply.result.value);
           }
+          const childViewport = await send<{
+            result: {
+              value: { width: number; height: number; clientWidth: number; clientHeight: number };
+            };
+          }>(
+            "Runtime.evaluate",
+            {
+              expression:
+                "({ width: innerWidth, height: innerHeight, clientWidth: document.documentElement.clientWidth, clientHeight: document.documentElement.clientHeight })",
+              returnByValue: true,
+            },
+            sessions[1],
+          );
+          for (const dimension of ["Width", "Height"] as const) {
+            const occupied =
+              childViewport.result.value[dimension === "Width" ? "width" : "height"] -
+              childViewport.result.value[`client${dimension}`];
+            if (
+              configuration.scrollbars === "both" ||
+              configuration.scrollbars === (dimension === "Width" ? "vertical" : "horizontal")
+            )
+              expect(occupied).toBeGreaterThan(0);
+            else expect(occupied).toBe(0);
+          }
           const facts = await captureObservationFacts(cdp, 1);
           expect(facts.issues).toEqual([]);
-          for (const frame of frames) {
-            const node = facts.documents
-              .find((doc) => doc.frame.frameId === frame.frameId)
-              ?.domNodes.find((node) => node.attrs.id === "probe");
-            expect(node, `missing probe in ${names.get(frame.frameId) || "root"}`).toBeDefined();
-            const local = oracles.get(frame.frameId)!.probe;
-            const top = { ...local };
-            let current = frame;
-            while (current.parentFrameId) {
-              const owner = oracles.get(current.parentFrameId)!.owners[names.get(current.frameId)!];
-              top.x = owner.x + top.x * owner.scale;
-              top.y = owner.y + top.y * owner.scale;
-              top.w *= owner.scale;
-              top.h *= owner.scale;
-              current = frames.find((item) => item.frameId === current.parentFrameId)!;
-            }
-            expect(
-              node!.rect,
-              JSON.stringify({
-                frame: names.get(frame.frameId),
-                local,
-                top,
-                viewport: facts.viewport,
-              }),
-            ).not.toBeNull();
-            for (const key of ["x", "y", "w", "h"] as const) {
-              expect(
-                Math.abs(node!.localRect![key] - local[key]),
-                `${names.get(frame.frameId)} local ${key}`,
-              ).toBeLessThan(2);
-              expect(
-                Math.abs(node!.rect![key] - top[key]),
-                `${names.get(frame.frameId)} top ${key}`,
-              ).toBeLessThan(2);
-            }
-          }
           expect(calls.filter((call) => call.endsWith(":Page.getLayoutMetrics"))).toHaveLength(
             sessions.length,
           );
+          // Identity verification also uses Runtime.evaluate; count the full viewport reads separately.
+          const viewportReadsBeforeLive = calls.filter((call) => call.endsWith(":viewport-size"));
+          expect(new Set(viewportReadsBeforeLive).size).toBe(viewportReadsBeforeLive.length);
+          expect(viewportReadsBeforeLive.length).toBeLessThanOrEqual(sessions.length - 1);
+          for (const frame of frames) {
+            for (const [id, local] of Object.entries(oracles.get(frame.frameId)!.probes)) {
+              const node = facts.documents
+                .find((doc) => doc.frame.frameId === frame.frameId)
+                ?.domNodes.find((node) => node.attrs.id === id);
+              expect(node, `missing ${id} in ${names.get(frame.frameId) || "root"}`).toBeDefined();
+              let top = clip(local, oracles.get(frame.frameId)!.viewport);
+              let current = frame;
+              while (top && current.parentFrameId) {
+                const parentOracle = oracles.get(current.parentFrameId)!;
+                const owner = parentOracle.owners[names.get(current.frameId)!];
+                top = clip(
+                  {
+                    x: owner.x + top.x * owner.scale,
+                    y: owner.y + top.y * owner.scale,
+                    w: top.w * owner.scale,
+                    h: top.h * owner.scale,
+                  },
+                  parentOracle.viewport,
+                );
+                current = frames.find((item) => item.frameId === current.parentFrameId)!;
+              }
+              for (const key of ["x", "y", "w", "h"] as const)
+                expect(
+                  Math.abs(node!.localRect![key] - local[key]),
+                  `${names.get(frame.frameId)} ${id} local ${key}`,
+                ).toBeLessThan(2);
+              if (!top) {
+                expect(node!.rect, `${id} must be clipped out`).toBeNull();
+                if (configuration.fixture === "oopif-scrollbars")
+                  expect(
+                    await resolveNodeGeometry(cdp, 1, {
+                      target: frame.target,
+                      frameId: frame.frameId,
+                      backendNodeId: node!.backendNodeId,
+                    }),
+                  ).toMatchObject({ code: "permission_denied" });
+                continue;
+              }
+              expect(node!.rect).not.toBeNull();
+              for (const key of ["x", "y", "w", "h"] as const)
+                expect(
+                  Math.abs(node!.rect![key] - top[key]),
+                  `${names.get(frame.frameId)} ${id} top ${key}`,
+                ).toBeLessThan(2);
+              if (configuration.fixture !== "oopif-scrollbars") continue;
+              const live = await resolveNodeGeometry(cdp, 1, {
+                target: frame.target,
+                frameId: frame.frameId,
+                backendNodeId: node!.backendNodeId,
+              });
+              if ("code" in live) throw new Error(live.message);
+              for (const [key, liveKey] of [
+                ["x", "x"],
+                ["y", "y"],
+                ["w", "width"],
+                ["h", "height"],
+              ] as const)
+                expect(
+                  Math.abs(live.topBounds[liveKey] - top[key]),
+                  `${id} live ${key}`,
+                ).toBeLessThan(2);
+              const before = server.snapshot("coordinates").events.length;
+              for (const type of ["mousePressed", "mouseReleased"])
+                await send(
+                  "Input.dispatchMouseEvent",
+                  { type, ...live.actionPoint, button: "left", clickCount: 1 },
+                  rootSession,
+                );
+              await expect
+                .poll(
+                  () =>
+                    server
+                      .snapshot("coordinates")
+                      .events.slice(before)
+                      .some(
+                        (event: { type: string; path: string; data: { probe?: string } }) =>
+                          event.type === "geometry.clicked" &&
+                          event.data.probe === id &&
+                          event.path ===
+                            (frame.parentFrameId
+                              ? names.get(frame.frameId) === "nested"
+                                ? "/oopif-scrollbars/nested"
+                                : "/oopif-scrollbars/frame"
+                              : "/oopif-scrollbars"),
+                      ),
+                  { timeout: 3000 },
+                )
+                .toBe(true);
+            }
+          }
           const metrics = await send<{
             cssVisualViewport: { zoom: number };
             visualViewport: { clientWidth: number };

apps/extension/src/tools/frame-geometry.ts

@@ -161,7 +161,8 @@ export async function resolveNodeGeometry(
         return geometryError(`could not resolve frame geometry for ${address.frameId}`);
       topVisibleRegions = projectRegionToViewport(localRegion, projection);
       if (address.target.sessionId) {
-        const localViewport = projection.edges[0]?.sourceViewport ?? projection.topViewport;
+        const localViewport = await context.viewport(address.target);
+        if (!localViewport) return geometryError("could not resolve target viewport geometry");
         const localVisibleRegions = localRegion
           .map((polygon) =>
             clipPolygon(

apps/extension/src/tools/geometry/frame-context.ts

@@ -9,8 +9,10 @@ import {
   type Polygon,
   type ProjectiveEdge,
   parseCdpQuad,
+  projectPolygon,
   type Quad,
   type Size,
+  viewportPolygon,
 } from "../geometry";
 import { type CdpRunner, sendToCdpTarget } from "../shared";
 import type { CoordinateOwner, CssViewport, SnapshotProjectionResult } from "./coordinate-types";
@@ -67,6 +69,7 @@ export function cssViewport(metrics: LayoutMetrics): CssViewport {
 /** One read-only measurement phase. Discard after scrolling or any later operation. */
 export class GeometryContext {
   private readonly metrics = new Map<string, Promise<LayoutMetrics>>();
+  private readonly frameViewports = new Map<string, Promise<Size | null>>();
   private readonly owners = new Map<string, Promise<Quad | null>>();
   private readonly projections = new Map<string, Promise<GeometryProjection | null>>();
   private readonly snapshotOwners = new Map<string, Promise<{ quad: Quad; size: Size } | null>>();
@@ -157,6 +160,35 @@ export class GeometryContext {
       : null;
   }
 
+  /** The full OOPIF viewport maps to its owner's content quad. Layout metrics
+   * exclude occupied scrollbars and remain the clipping boundary, not the scale. */
+  private frameViewport(target: CdpTarget): Promise<Size | null> {
+    const key = cdpTargetKey(target);
+    let promise = this.frameViewports.get(key);
+    if (!promise) {
+      promise = this.request<{ result?: { value?: Size }; exceptionDetails?: unknown }>(
+        target,
+        "Runtime.evaluate",
+        {
+          expression: "({ width: window.innerWidth, height: window.innerHeight })",
+          returnByValue: true,
+        },
+      ).then(({ result, exceptionDetails }) => {
+        const size = result?.value;
+        return !exceptionDetails &&
+          size &&
+          Number.isFinite(size.width) &&
+          Number.isFinite(size.height) &&
+          size.width > 0 &&
+          size.height > 0
+          ? size
+          : null;
+      });
+      this.frameViewports.set(key, promise);
+    }
+    return promise;
+  }
+
   ownerContent(target: CdpTarget, backendNodeId: number): Promise<Quad | null> {
     const key = `${cdpTargetKey(target)}:${backendNodeId}`;
     let promise = this.owners.get(key);
@@ -342,12 +374,19 @@ export class GeometryContext {
       const parent = frames.get(root.parentFrameId);
       if (!parent || root.ownerBackendNodeId === undefined) return null;
       const destinationQuad = await this.ownerContent(parent.target, root.ownerBackendNodeId);
-      const source = await this.viewport(root.target);
+      if (!destinationQuad) return null;
+      const source = await this.frameViewport(root.target);
+      const visible = await this.viewport(root.target);
       const parentRoot = this.targetRoot(frames, parent);
-      if (!destinationQuad || !source || !parentRoot) return null;
+      if (!source || !visible || !parentRoot) return null;
       const destinationClips = await this.clips(frames, parent, parentRoot);
       if (!destinationClips) return null;
-      edges.push({ sourceViewport: source, destinationQuad, destinationClips });
+      const edge = { sourceViewport: source, destinationQuad, destinationClips };
+      // Keep scrollbar strips clipped at every target boundary, including
+      // intermediate OOPIFs. Project the clip with the same full-viewport scale.
+      if (source.width !== visible.width || source.height !== visible.height)
+        destinationClips.push(projectPolygon(viewportPolygon(visible), edge));
+      edges.push(edge);
       root = parentRoot;
     }
     const topViewport = await this.viewport(root.target);

apps/extension/src/tools/vom/__tests__/capture-coordinator.test.ts

@@ -655,6 +655,7 @@ function childSnapshot(frameId: string, backendNodeId: number) {
 describe("OOPIF capture", () => {
   it("captures and positions multiple OOPIF documents missing from the root snapshot", async () => {
     const sendToTarget = vi.fn(async (target, method) => {
+      if (method === "Runtime.evaluate") return { result: { value: { width: 300, height: 200 } } };
       if (method === "Page.getLayoutMetrics") {
         return {
           visualViewport: { clientWidth: 1000 },