fix(desktop): preview snapshots no longer stall on Chromium's legacy capture path

apps/desktop/src/app/DesktopEarlyElectronStartup.ts

@@ -138,6 +138,25 @@ export function resolveLinuxDisableFeaturesSwitch(input: {
     : `${input.disableFeatures},${WAYLAND_COLOR_MANAGER_FEATURE}`;
 }
 
+// Playwright enables this when it launches Chromium; T3 launches Electron itself and attaches
+// over CDP, so preview snapshots would otherwise use the legacy capture path that can stall.
+const CDP_SCREENSHOT_NEW_SURFACE_FEATURE = "CDPScreenshotNewSurface";
+
+export function resolveEnableFeaturesSwitch(input: {
+  readonly enableFeatures: string | null;
+  readonly disableFeatures: string | null;
+}): string | null {
+  if (featureListNames(input.enableFeatures).includes(CDP_SCREENSHOT_NEW_SURFACE_FEATURE)) {
+    return null;
+  }
+  if (featureListNames(input.disableFeatures).includes(CDP_SCREENSHOT_NEW_SURFACE_FEATURE)) {
+    return null;
+  }
+  return input.enableFeatures === null
+    ? CDP_SCREENSHOT_NEW_SURFACE_FEATURE
+    : `${input.enableFeatures},${CDP_SCREENSHOT_NEW_SURFACE_FEATURE}`;
+}
+
 export function resolveEarlyLinuxElectronOptions(
   input: EarlyLinuxElectronOptionsInput,
 ): EarlyLinuxElectronOptions {

apps/desktop/src/app/DesktopPreReadyPlatform.test.ts

@@ -120,6 +120,55 @@ describe("DesktopPreReadyPlatform", () => {
     );
   });
 
+  const launchWithCommandLine = (
+    platform: NodeJS.Platform,
+    initialSwitches: ReadonlyArray<readonly [string, string]>,
+  ) => {
+    const commandLine = new Map(initialSwitches);
+    hasSwitchMock.mockImplementation((name: string) => commandLine.has(name));
+    getSwitchValueMock.mockImplementation((name: string) => commandLine.get(name) ?? "");
+    appendSwitchMock.mockImplementation((name: string, value: string) => {
+      commandLine.set(name, value);
+    });
+    return DesktopPreReadyPlatform.make.pipe(
+      Effect.provideService(HostProcess.Platform, platform),
+      Effect.as(commandLine),
+    );
+  };
+
+  it.effect.each(["darwin", "win32", "linux"] as const)(
+    "enables a fresh capture surface for CDP screenshots on %s",
+    (platform) =>
+      Effect.gen(function* () {
+        const commandLine = yield* launchWithCommandLine(platform, []);
+        assert.sameMembers(commandLine.get("enable-features")?.split(",") ?? [], [
+          "CDPScreenshotNewSurface",
+        ]);
+      }),
+  );
+
+  it.effect("keeps features already enabled on the command line", () =>
+    Effect.gen(function* () {
+      const commandLine = yield* launchWithCommandLine("darwin", [
+        ["enable-features", "WebRTCPipeWireCapturer,UseOzonePlatform"],
+      ]);
+      assert.sameMembers(commandLine.get("enable-features")?.split(",") ?? [], [
+        "WebRTCPipeWireCapturer",
+        "UseOzonePlatform",
+        "CDPScreenshotNewSurface",
+      ]);
+    }),
+  );
+
+  it.effect("respects a user who disabled the fresh capture surface", () =>
+    Effect.gen(function* () {
+      const commandLine = yield* launchWithCommandLine("darwin", [
+        ["disable-features", "CDPScreenshotNewSurface"],
+      ]);
+      assert.isFalse(commandLine.has("enable-features"));
+    }),
+  );
+
   it.effect.each([
     { previousEntry: undefined, label: "missing" },
     { previousEntry: 'Exec="/Applications/deleted-previous.AppImage" %U', label: "stale" },
@@ -243,7 +292,10 @@ describe("DesktopPreReadyPlatform", () => {
         });
         assert.deepEqual(events, ["pre-ready", "clerk"]);
         assert.equal(registerSchemesMock.mock.calls.length, 1);
-        assert.equal(appendSwitchMock.mock.calls.length, 0);
+        assert.deepEqual(
+          appendSwitchMock.mock.calls.map(([name]) => name),
+          ["enable-features"],
+        );
         assert.equal(setDesktopNameMock.mock.calls.length, 0);
       }),
   );

apps/desktop/src/app/DesktopPreReadyPlatform.ts

@@ -157,6 +157,14 @@ export const make = Effect.gen(function* () {
       }
     }
 
+    const enableFeatures = DesktopEarlyElectronStartup.resolveEnableFeaturesSwitch({
+      enableFeatures: readCommandLineSwitchValue(Electron.app.commandLine, "enable-features"),
+      disableFeatures: readCommandLineSwitchValue(Electron.app.commandLine, "disable-features"),
+    });
+    if (enableFeatures !== null) {
+      Electron.app.commandLine.appendSwitch("enable-features", enableFeatures);
+    }
+
     return { linux, linuxPasswordStoreCommandLine };
   });
 }).pipe(Effect.withSpan("desktop.electron.configureBeforeReady"));