fix(sim): text-width/render bugs, splash version, wasm-fetch error, battery lag

Code-review pass over the buzzer/sim commits turned up several real bugs,
plus two issues found afterward from manual browser testing:

Rendering (SimDisplayDriverCanvas, variants/sim/SimDisplayDriver.h + target.cpp):
- getTextWidth() measured UTF-8 BYTES (strlen()*6), not codepoints. Since
  b067e95b stopped stripping accents, any accented string now measures
  double its real width -- mis-centred titles, premature ellipsis/marquee,
  badges pushed off-screen. Now uses the real MiscFixedRenderer measurement
  (miscFixedTextWidth()), same as SH1106Display/SSD1306Display.
- Added the matching getCodepointWidth() override (O(1) single-glyph
  advance), same pattern as SSD1306Display.
- isSingleFont() was left at the base class's `false`, though this backend
  only ever renders MiscFixed -- UITask.cpp's status-bar indicator height
  keys off this (`lh-2` vs `lh`), so the sim drew it 2px taller than a real
  board.
- print() blitted the full 128x64 canvas on every call (dozens per frame,
  60fps) -- now tracks a dirty bounding box and only clears/blits the
  region actually touched.

Web Audio (buzzer bridge, index.html + mesh.html):
- No AudioContext.resume() -- a context created (or later suspended) in the
  'suspended' state (Safari/Firefox, or any browser backgrounding the tab)
  stayed silent forever. Now resumed on every gesture.
- linearRampToValueAtTime with no anchoring setValueAtTime interpolates
  from the LAST scheduled event, not "now" -- so the anti-click ramps could
  effectively snap instead of fading. Fixed with cancelScheduledValues +
  setValueAtTime(current) before each ramp.
- mesh.html: a gesture only armed the clicked instance's audio. Click A,
  send A->B, and B (the one actually meant to beep on receipt) stayed
  silent. Now any gesture arms both A and B.
- RTTTL rests (freq=0, still "playing") now explicitly hold pitch and drop
  gain instead of it happening to work by coincidence.

Misc: sim_test_get_num_contacts() was missing the g_sim_ready gate every
other sim_test_* hook has, so it could return a bogus negative count before
setup() finishes seeding num_contacts.

Splash screen missing "Solo <version>" bar: variants/sim never defined
FIRMWARE_SOLO_BUILD (every real Solo board does), so SplashScreen silently
skipped that whole line -- the sim looked like a plain non-Solo companion
build. Added -D FIRMWARE_SOLO_BUILD=1 to platformio.ini and build_wasm.sh.
Verified on a real canvas screenshot: "MESHCORE 1.17.1 / 19 Aug 2026 /
Solo v1.27".

Wasm-fetch error message: "failed to start: RuntimeError: Aborted(both
async and sync fetching of the wasm failed)" is Emscripten's own opaque
message for the single most common real cause -- the page opened via
file://...index.html instead of served over http(s) (fetch() on a local
file is blocked by CORS in both Chrome and Safari, confirmed by reproducing
the exact same error/stack via file://). Both harnesses now detect
location.protocol === 'file:' and show an actionable message with the
one-line fix instead of the raw stack trace.

Battery-set latency: SimMainBoard's battery value is an exact, instantaneous
JS-set integer (see sim_battery_set_mv()), but UITask's battery-check code
polls it every 8s and runs it through an EMA (alpha=0.2) meant to smooth a
REAL board's noisy ADC -- so a value typed into the demo UI could take tens
of seconds to visibly settle. SIM_PLATFORM now checks every 250ms and skips
the EMA (nothing to smooth), since the reading is already clean. Measured
on real canvas pixels: indicator update now lands within one screen-refresh
cycle instead of up to 8s+.

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

examples/companion_radio/main.cpp

@@ -402,6 +402,10 @@ extern "C" EMSCRIPTEN_KEEPALIVE int sim_test_send_msg_to_first_contact(const cha
 // the JS ether-tick loop poll "has advert propagation finished yet" without
 // guessing a fixed timeout.
 extern "C" EMSCRIPTEN_KEEPALIVE int sim_test_get_num_contacts() {
+  // Same g_sim_ready gate as every other hook here: before setup() runs,
+  // BaseChatMesh::num_contacts hasn't been seeded to MAX_ANON_CONTACTS yet,
+  // so getNumContacts() would report a negative count.
+  if (!g_sim_ready) return 0;
   return the_mesh.getNumContacts();
 }
 

examples/companion_radio/ui-new/UITask.cpp

@@ -2456,7 +2456,8 @@ void UITask::loop() {
   // above, in the #if defined(SIM_PLATFORM) && defined(__EMSCRIPTEN__)
   // block) -- this stdin-poll branch was only ever meant for Phase 1's
   // native terminal target.
-  // Native terminal input: stdin is put into raw/non-canonical mode by
+  //
+  // stdin is put into raw/non-canonical mode by
   // variants/sim/sim_main.cpp's main(), so keys arrive here one at a time
   // with no Enter-to-submit line buffering. Non-blocking select() on fd 0
   // (VMIN=0/VTIME=0 on the fd itself would also work, but select() keeps
@@ -2752,8 +2753,20 @@ void UITask::loop() {
   if ((int32_t)(millis() - next_batt_chck) >= 0) {
     uint16_t raw = AbstractUITask::getBattMilliVolts();
     if (raw > 0) {
+#ifdef SIM_PLATFORM
+      // SimMainBoard::getBattMilliVolts() returns exactly whatever value the
+      // host page's JS last set (see sim_battery_set_mv() in
+      // variants/sim/SimMainBoard.h) -- a clean, instantaneous number, not a
+      // noisy ADC reading. Real hardware needs the EMA below to smooth a
+      // voltage divider's jitter under load; applying that same filter here
+      // just makes a value typed into the demo UI visibly crawl toward its
+      // target over several 8s samples, which reads as the whole sim being
+      // laggy for no benefit the sim actually needs.
+      _batt_mv = raw;
+#else
       // EMA filter: alpha=0.2 (80% old, 20% new) — smooths ADC noise from uneven load
       _batt_mv = (_batt_mv == 0) ? raw : (uint16_t)((_batt_mv * 4u + raw) / 5u);
+#endif
     }
     uint16_t low_mv = _node_prefs ? _node_prefs->low_batt_mv : 0;
     // Don't shut down while on external power (charging) — avoids a shutdown loop.
@@ -2775,7 +2788,16 @@ void UITask::loop() {
       }
       shutdown();
     }
+#ifdef SIM_PLATFORM
+    // A real ADC read has a real cost, worth spacing out 8s apart; the sim's
+    // "read" is just returning a JS-set integer, so there's no reason to sit
+    // on a stale value for up to 8s after Set was clicked. 250ms keeps this
+    // a poll (not a push wired to the input's own event, which would need
+    // its own plumbing) while feeling immediate.
+    next_batt_chck = millis() + 250;
+#else
     next_batt_chck = millis() + 8000;
+#endif
   }
 
   // GPS duty-cycle hold — tells the sensor manager whether *anything* needs

examples/companion_radio/ui-new/UITask.h

@@ -230,7 +230,10 @@ public:
 #ifdef PIN_BUZZER
   // Lets a host page poll the buzzer's current state every frame to drive a
   // Web Audio oscillator (see sim_buzzer_is_playing()/sim_buzzer_freq_hz()
-  // in main.cpp) -- `buzzer` itself is a private member, so a free function
+  // in UITask.cpp, next to sim_enqueue_key() -- they live there, not in
+  // main.cpp, because the `g_sim_ui_task_for_js` pointer they dispatch
+  // through is file-static to that translation unit) -- `buzzer` itself is a
+  // private member, so a free function
   // outside this class needs these to reach it, same reason injectSimKey()
   // above is public.
   // Not const: genericBuzzer::isPlaying() itself isn't const-qualified (its