fix(sim): boot silent (video off, audio 0) — no un-gestured auto-start

The post-load autoStart() flipped Video on and lifted audio to 3/10 with no
user gesture. Browser autoplay policy blocks an audio play() made outside a
gesture (muted video survives, sound does not), so auto-start showed video but
stayed silent. Boot SILENT instead and wait for the operator to turn Video on —
that click IS the gesture, and its handler couples audio to 3/10 and starts the
soundtrack in-gesture, so sound reliably comes up with video.

Updates the pytest e2e + Playwright e2e specs to assert boot-silent + the
video-on-couples-audio wiring instead of the old auto-start wiring.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

tests/test_e2e_audio.py

@@ -2,12 +2,15 @@
 cleanly when Playwright or its browser binary is absent.
 
 NOTE: headless engines relax BOTH autoplay and GPU compositing, so these assert
-the WIRING (auto-start on load, dial→play/volume, video-off blanking) — real
-Safari/iOS autoplay and real-GPU compositing still need a device by-ear/eye check.
+the WIRING (boot-silent, video-on couples audio, dial→play/volume, video-off
+blanking) — real Safari/iOS autoplay and real-GPU compositing still need a device
+by-ear/eye check.
 
-The experience AUTO-STARTS once the preload finishes: Video turns on and the audio
-level dial rises to 3/10 with no user gesture (app.js autoStart()). Audio is a 0–10
-range dial (not a checkbox); set it by writing `value` + firing an `input` event.
+The experience BOOTS SILENT — video off, audio dial at 0 — so nothing plays until a
+real user gesture. Turning Video ON (a click) couples the audio dial up to 3/10 and
+starts the soundtrack IN that gesture, sidestepping the browser autoplay block that
+swallowed an un-gestured auto-start. Audio is a 0–10 range dial (not a checkbox);
+set it by writing `value` + firing an `input` event.
 
 Install:  pip install -e '.[e2e]' && python -m playwright install chromium
 """
@@ -63,7 +66,7 @@ def page(app_url):
         pg = browser.new_page()
         pg.goto(app_url)
         # wait out the "Loading Universe…" splash (it overlays + blocks clicks); the
-        # auto-start fires as it dismisses.
+        # experience boots silent (video off, audio 0) as it dismisses.
         pg.wait_for_selector("#loading", state="detached", timeout=60000)
         yield pg
         browser.close()
@@ -84,10 +87,23 @@ def _set_audio(page, level):
     )
 
 
-def test_app_auto_starts_video_and_audio(page):
-    # Once the preload finishes the experience auto-starts: Video on + audio at 3/10,
-    # video showing (black hidden), a scale soundtrack playing — no tap-to-start wall.
-    assert page.is_checked("#visual") is True
+def test_app_boots_silent_video_off(page):
+    # The experience boots SILENT: Video off, audio dial at 0, screen black, both
+    # crossfade elements paused — nothing plays until a real user gesture.
+    assert page.is_checked("#visual") is False
+    assert page.evaluate("document.getElementById('audio').value") == "0"
+    assert page.evaluate("document.getElementById('audio-level-val').textContent") == "0"
+    page.wait_for_selector("#black:not(.hidden)")                      # screen blanked
+    assert page.evaluate(
+        "(() => { const a = document.getElementById('aud'), b = document.getElementById('aud-b');"
+        " return a.paused && b.paused; })()"
+    ) is True
+
+
+def test_video_on_couples_audio_to_three_and_plays(page):
+    # Turning Video on (a click gesture) lifts the audio dial to 3/10 and starts the
+    # soundtrack IN that gesture: video shows (black hidden), a scale soundtrack plays.
+    _toggle_visual(page)                                                # off -> on
     page.wait_for_function("document.getElementById('audio').value === '3'")
     page.wait_for_function("document.getElementById('audio-level-val').textContent === '3'")
     page.wait_for_selector("#black.hidden", state="attached")          # video showing
@@ -113,8 +129,11 @@ def test_audio_dial_zero_silences(page):
     assert page.evaluate("document.getElementById('audio').value") == "0"
 
 
-def test_video_off_blanks_after_autostart(page):
-    # Video is auto-on; turning it off blanks the screen and hides the GPU layers.
+def test_video_off_blanks(page):
+    # Turn Video on (boot is off), then off again: that blanks the screen and hides
+    # the GPU layers.
+    _toggle_visual(page)                                                # off -> on
+    page.wait_for_selector("#black.hidden", state="attached")
     _toggle_visual(page)                                                # on -> off
     page.wait_for_selector("#black:not(.hidden)")
     page.wait_for_function(