fix(screenshot): hide overlays during capture so shots only contain page content (#64)

apps/extension/src/content/__tests__/capture-suppress.test.ts

@@ -0,0 +1,125 @@
+import { beforeEach, describe, expect, it, vi } from "vitest";
+import { CAPTURE_SUPPRESS, type CaptureSuppressAck } from "@/lib/capture-suppress-bridge";
+import { CAPTURE_HIDDEN_ATTR, createCaptureSuppressController } from "../capture-suppress";
+
+/**
+ * rAF is stubbed with a manual queue so tests can drive the compositor
+ * frame-by-frame and assert the ack only lands after the second frame.
+ */
+describe("capture-suppress controller", () => {
+  let rafQueue: FrameRequestCallback[];
+  let host: HTMLElement;
+
+  beforeEach(() => {
+    rafQueue = [];
+    vi.stubGlobal("requestAnimationFrame", (cb: FrameRequestCallback) => {
+      rafQueue.push(cb);
+      return rafQueue.length;
+    });
+    vi.stubGlobal("cancelAnimationFrame", vi.fn());
+    document.body.innerHTML = "";
+    host = document.createElement("div");
+    document.body.append(host);
+  });
+
+  /** Run every queued rAF callback, draining microtasks between rounds. */
+  async function flushFrames(rounds = 4): Promise<void> {
+    for (let round = 0; round < rounds && rafQueue.length > 0; round += 1) {
+      const callbacks = rafQueue.splice(0);
+      for (const cb of callbacks) cb(0);
+      await Promise.resolve();
+      await Promise.resolve();
+    }
+  }
+
+  it("begin hides the host immediately but only acks after two frames", async () => {
+    const controller = createCaptureSuppressController(() => host);
+    const sendResponse = vi.fn();
+
+    const needsAsync = controller.handleMessage(
+      { type: CAPTURE_SUPPRESS, phase: "begin" },
+      sendResponse,
+    );
+
+    expect(needsAsync).toBe(true);
+    expect(controller.pendingCount).toBe(1);
+    expect(host.hasAttribute(CAPTURE_HIDDEN_ATTR)).toBe(true);
+    expect(sendResponse).not.toHaveBeenCalled();
+
+    // First frame commits the style change; the ack must still be pending.
+    await flushFrames(1);
+    expect(sendResponse).not.toHaveBeenCalled();
+
+    // Second frame: the compositor has produced an overlay-free frame.
+    await flushFrames();
+    const expected: CaptureSuppressAck = { type: CAPTURE_SUPPRESS, ok: true };
+    expect(sendResponse).toHaveBeenCalledWith(expected);
+  });
+
+  it("end removes the attribute once the count returns to zero", async () => {
+    const controller = createCaptureSuppressController(() => host);
+    controller.handleMessage({ type: CAPTURE_SUPPRESS, phase: "begin" }, vi.fn());
+    await flushFrames();
+    expect(host.hasAttribute(CAPTURE_HIDDEN_ATTR)).toBe(true);
+
+    const sendResponse = vi.fn();
+    const needsAsync = controller.handleMessage(
+      { type: CAPTURE_SUPPRESS, phase: "end" },
+      sendResponse,
+    );
+
+    expect(needsAsync).toBe(false);
+    expect(controller.pendingCount).toBe(0);
+    expect(host.hasAttribute(CAPTURE_HIDDEN_ATTR)).toBe(false);
+    expect(sendResponse).toHaveBeenCalledWith({ type: CAPTURE_SUPPRESS, ok: true });
+  });
+
+  it("reference-counts concurrent begins so one end does not unhide early", async () => {
+    const controller = createCaptureSuppressController(() => host);
+    controller.handleMessage({ type: CAPTURE_SUPPRESS, phase: "begin" }, vi.fn());
+    controller.handleMessage({ type: CAPTURE_SUPPRESS, phase: "begin" }, vi.fn());
+    await flushFrames();
+    expect(controller.pendingCount).toBe(2);
+
+    controller.handleMessage({ type: CAPTURE_SUPPRESS, phase: "end" }, vi.fn());
+    expect(controller.pendingCount).toBe(1);
+    expect(host.hasAttribute(CAPTURE_HIDDEN_ATTR)).toBe(true);
+
+    controller.handleMessage({ type: CAPTURE_SUPPRESS, phase: "end" }, vi.fn());
+    expect(controller.pendingCount).toBe(0);
+    expect(host.hasAttribute(CAPTURE_HIDDEN_ATTR)).toBe(false);
+  });
+
+  it("treats a stray end as a no-op", () => {
+    const controller = createCaptureSuppressController(() => host);
+    const sendResponse = vi.fn();
+
+    controller.handleMessage({ type: CAPTURE_SUPPRESS, phase: "end" }, sendResponse);
+
+    expect(controller.pendingCount).toBe(0);
+    expect(host.hasAttribute(CAPTURE_HIDDEN_ATTR)).toBe(false);
+    expect(sendResponse).toHaveBeenCalledWith({ type: CAPTURE_SUPPRESS, ok: true });
+  });
+
+  it("re-applies the attribute when the host is remounted mid-capture", () => {
+    let currentHost: HTMLElement | null = host;
+    const controller = createCaptureSuppressController(() => currentHost);
+    controller.handleMessage({ type: CAPTURE_SUPPRESS, phase: "begin" }, vi.fn());
+
+    // Host lost and rebuilt before `end` arrives.
+    currentHost = null;
+    const rebuilt = document.createElement("div");
+    controller.onHostMounted(rebuilt);
+
+    expect(rebuilt.hasAttribute(CAPTURE_HIDDEN_ATTR)).toBe(true);
+  });
+
+  it("leaves a remounted host visible once suppression has ended", () => {
+    const controller = createCaptureSuppressController(() => host);
+    const rebuilt = document.createElement("div");
+
+    controller.onHostMounted(rebuilt);
+
+    expect(rebuilt.hasAttribute(CAPTURE_HIDDEN_ATTR)).toBe(false);
+  });
+});

apps/extension/src/content/capture-suppress.ts

@@ -0,0 +1,99 @@
+/**
+ * Content-script side of the capture-suppress bridge: hides the overlay
+ * shadow host while the background captures a screenshot.
+ *
+ * `begin` sets `data-bsk-capture-hidden` on the host (overlay.css maps it
+ * to `display: none !important`, which removes the whole shadow subtree
+ * from compositing) and only acks after two animation frames — the first
+ * frame commits the style change, the second guarantees the compositor
+ * has produced a frame without the overlay, so the capture API cannot
+ * pick up a stale frame that still contains it. `end` is
+ * reference-counted so overlapping captures do not unhide the host early.
+ */
+
+import {
+  CAPTURE_SUPPRESS,
+  type CaptureSuppressAck,
+  type CaptureSuppressMessage,
+} from "@/lib/capture-suppress-bridge";
+
+export const CAPTURE_HIDDEN_ATTR = "data-bsk-capture-hidden";
+
+/**
+ * Safety net for hidden/background tabs where rAF callbacks never fire:
+ * the attribute is already set synchronously, so any frame the compositor
+ * produces from now on excludes the overlay. Waiting longer would just
+ * deadlock the capture.
+ */
+const FRAME_FALLBACK_MS = 500;
+
+function nextFrame(): Promise<void> {
+  return new Promise((resolve) => {
+    const raf = requestAnimationFrame(() => {
+      clearTimeout(timer);
+      resolve();
+    });
+    const timer = setTimeout(() => {
+      cancelAnimationFrame(raf);
+      resolve();
+    }, FRAME_FALLBACK_MS);
+  });
+}
+
+export interface CaptureSuppressController {
+  /**
+   * Handle one bridge message. Returns true when the ack is sent
+   * asynchronously and the caller must keep the message channel open.
+   */
+  handleMessage(
+    message: CaptureSuppressMessage,
+    sendResponse: (ack: CaptureSuppressAck) => void,
+  ): boolean;
+  /** Re-apply the hidden attribute when the overlay host is (re)mounted. */
+  onHostMounted(host: HTMLElement): void;
+  /** Number of in-flight `begin` phases (exposed for tests). */
+  readonly pendingCount: number;
+}
+
+export function createCaptureSuppressController(
+  getHost: () => HTMLElement | null,
+): CaptureSuppressController {
+  let pending = 0;
+
+  const ack: CaptureSuppressAck = { type: CAPTURE_SUPPRESS, ok: true };
+
+  function setHidden(host: HTMLElement | null, hidden: boolean): void {
+    if (!host) return;
+    if (hidden) host.setAttribute(CAPTURE_HIDDEN_ATTR, "");
+    else host.removeAttribute(CAPTURE_HIDDEN_ATTR);
+  }
+
+  return {
+    get pendingCount() {
+      return pending;
+    },
+    handleMessage(message, sendResponse) {
+      if (message.phase === "begin") {
+        pending += 1;
+        setHidden(getHost(), true);
+        void (async () => {
+          await nextFrame();
+          await nextFrame();
+          sendResponse(ack);
+        })();
+        return true;
+      }
+      // `end` without a matching `begin` (e.g. a retried message) must not
+      // drive the counter negative or clear a concurrent capture's flag.
+      pending = Math.max(0, pending - 1);
+      if (pending === 0) setHidden(getHost(), false);
+      sendResponse(ack);
+      return false;
+    },
+    onHostMounted(host) {
+      // Host lost + rebuilt mid-capture: the fresh host must stay hidden
+      // until the last `end` arrives.
+      setHidden(host, pending > 0);
+    },
+  };
+}

apps/extension/src/content/overlay.css

@@ -14,3 +14,10 @@
 :host([data-bsk-overlay-surface][data-bsk-overlay-blocking]) {
   pointer-events: auto !important;
 }
+
+/* Screenshot suppression: the host lives in the main DOM, so hiding it
+   removes the whole shadow subtree from compositing and captured frames
+   only contain page content. */
+:host([data-bsk-capture-hidden]) {
+  display: none !important;
+}