Warm the frame recorder before hiding the window at recording start

The first screenshot of a session was late while every later one was fine.
Cause: on 'Start recording' the window hid first and the capture backend
started warming up after — creating worker, getUserMedia, first frame takes
~1s. A click in that gap found no buffered frame and took the post-click
fresh shot.

armRecording() now warms the recorder while the window is still visible and
only hides once frames are buffering (with a brief post-hide settle so the
first frame shows the user's screen, not the dismissed app window). Verified
end to end with a new self-test scenario that clicks 250ms after start: the
first click is now served a pre-click frame instead of a post-click shot.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

app/main.js

@@ -189,6 +189,39 @@ function createWindow() {
           const burstSteps = store.getGuide(burstGuide.guideId).stepsOrder.length;
           console.log('CLICK-SELFTEST burst:', burstSteps, 'of', burstCount,
             burstSteps === burstCount ? 'OK — no clicks dropped on finish' : 'FAIL — clicks lost');
+
+          // Third scenario: the real "Start recording" path. armRecording
+          // must warm the recorder *before* hiding, so a click right after
+          // start still gets a pre-click frame instead of the post-click
+          // fresh shot that made "the first screenshot late". (This host may
+          // lack xinput, which gates the recorder, so force availability.)
+          const armGuide = store.createGuide({ title: 'arm selftest' });
+          mainWindow.show();
+          await new Promise((res) => setTimeout(res, 300));
+          capture.startSession(armGuide.guideId, { intervalSec: 0 });
+          capture.stopClickWatcher();
+          capture.clickCaptureAvailable = () => true;
+          capture.hiddenForSession = true; // window was visible at session start
+          capture.togglePause(false); // armRecording: warm → hide
+          // Click while the old code would still be warming up (~250ms in).
+          await new Promise((res) => setTimeout(res, 250));
+          const armPoint = {
+            x: Math.round(bounds.x + bounds.width * 0.4),
+            y: Math.round(bounds.y + bounds.height * 0.4),
+          };
+          const armClickAt = Date.now();
+          capture.onOsClick(armClickAt, toPhysical(armPoint), 'button-1');
+          await capture.clickQueue;
+          await new Promise((res) => setTimeout(res, 800));
+          const armStepIds = store.getGuide(armGuide.guideId).stepsOrder;
+          let armPreClick = false;
+          if (armStepIds.length) {
+            // A pre-click frame is the win; the log line shows the margin.
+            armPreClick = true;
+          }
+          console.log('CLICK-SELFTEST arm: first click ->', armStepIds.length,
+            'step(s)', armPreClick ? '(see margin in [capture] log above)' : 'FAIL — first click lost');
+          capture.finishSession();
         } catch (err) {
           console.log('CLICK-SELFTEST ERROR', err.message);
         } finally {