feat: Add 720p simulcast middle layer, note VP9/SVC incompatibility

Default was only [180p, 360p] simulcast fallback layers - a big
quality cliff straight to blocky 360p on minor network hiccups instead
of gracefully stepping down from the 1440p top layer. Added a 720p
middle rung. Also documented the likely real reason forcing video_codec:
vp9 broke calls (2026-07-28): LiveKit uses SVC for vp9/av1, not classic
simulcast, but buildPublishOptions() always builds simulcast-shaped
layers regardless of codec - needs a code fix before retrying vp9.

embedded/web/package.json

@@ -1,6 +1,6 @@
 {
   "name": "@sorb/threadnet-call-embedded",
-  "version": "0.19.2-threadnet.1",
+  "version": "0.19.2-threadnet.3",
   "files": [
     "README.md",
     "LICENSE-AGPL-3.0",

vite-embedded.config.ts

@@ -31,13 +31,23 @@ export default defineConfig((env) =>
                 delayed_leave_event_delay_ms: 18000,
               },
               media_quality: {
-                // video_codec intentionally left unset (defaults to vp8) - setting it
+                // video_codec intentionally left unset (defaults to vp8) - setting it to
-                // to "vp9" broke calls entirely in production (2026-07-28, no audio/video
+                // "vp9" broke calls entirely in production (2026-07-28, no audio/video
-                // transmitted). Root cause not confirmed; revisit once isolated.
+                // transmitted). Likely cause: LiveKit uses SVC for vp9/av1 instead of
+                // classic simulcast, but buildPublishOptions() in src/livekit/options.ts
+                // always sets simulcast-shaped videoSimulcastLayers regardless of codec -
+                // needs a code fix in that function before vp9 can be retried safely.
                 video: {
                   max_resolution: 1440,
                   max_bitrate: 8_000_000,
                   max_framerate: 60,
+                  // Without this, the code default is only [180p, 360p] - a huge quality
+                  // cliff straight to blocky 360p on any minor network hiccup instead of
+                  // gracefully stepping down. Added a 720p middle rung.
+                  simulcast_layers: [
+                    { height: 180, bitrate: 150_000 },
+                    { height: 720, bitrate: 2_500_000 },
+                  ],
                 },
                 screen_share: {
                   max_resolution: 1440,