feat(nests): emit catalog jitter hint matching Opus frame duration

hang.js's encoder publishes a `jitter` field (ms) in every audio
rendition; the watcher uses it to size its jitter buffer. Without it
the watcher falls back to a built-in default — works in practice today
but means our publishes deviate from the canonical hang shape and the
deviation could surface as audible buffer-sizing differences on a
future watcher revision that takes the field as required.

Add `jitter: 20` to MoqLiteHangCatalog.AudioRendition (matching the
Opus frame cadence: 960 samples at 48 kHz = 20 ms; same value hang.js
hard-codes at `js/publish/src/audio/encoder.ts:#runConfig`). Updates
the byte-exact MoqLiteHangCatalogTest assertion and the parallel
inline-literal in RoomSpeakerCatalogTest so both sides stay pinned.

The commons-side `RoomSpeakerCatalog` parser doesn't surface the new
field — `JsonMapper`'s `ignoreUnknownKeys = true` lets the watcher
ingest it silently. Adding a typed `jitter` field there is a
forward-compat task; not needed for interop with hang today.

https://claude.ai/code/session_014JfZJHSTvyYYWJbC9VbB47

commons/src/commonTest/kotlin/com/vitorpamplona/amethyst/commons/viewmodels/RoomSpeakerCatalogTest.kt

@@ -137,7 +137,7 @@ class RoomSpeakerCatalogTest {
         val emitted =
             "{\"audio\":{\"renditions\":{\"audio/data\":{" +
                 "\"codec\":\"opus\",\"container\":{\"kind\":\"legacy\"}," +
-                "\"sampleRate\":48000,\"numberOfChannels\":1}}}}"
+                "\"sampleRate\":48000,\"numberOfChannels\":1,\"jitter\":20}}}}"
         val catalog = RoomSpeakerCatalog.parseOrNull(emitted.encodeToByteArray())
         assertNotNull(catalog)
         val rendition = catalog.primaryAudio()
@@ -146,5 +146,10 @@ class RoomSpeakerCatalogTest {
         assertEquals("legacy", rendition.container?.kind)
         assertEquals(48_000, rendition.sampleRate)
         assertEquals(1, rendition.numberOfChannels)
+        // `jitter` is intentionally not asserted on `rendition` — the
+        // commons-side parser drops unknown fields via the JsonMapper's
+        // `ignoreUnknownKeys = true`. Adding it to `RoomSpeakerCatalog`
+        // is forward work; the byte-exact match in the literal above
+        // already pins the wire shape.
     }
 }

nestsClient/src/commonMain/kotlin/com/vitorpamplona/nestsclient/moq/lite/MoqLiteHangCatalog.kt

@@ -40,6 +40,7 @@ import kotlinx.serialization.json.Json
  *           "container": { "kind": "legacy" },
  *           "sampleRate": 48000,
  *           "numberOfChannels": 1,
+ *           "jitter": 20,              // ms; matches one Opus frame
  *           "bitrate": 32000           // optional
  *         }
  *       }
@@ -67,6 +68,15 @@ internal data class MoqLiteHangCatalog(
         val container: Container,
         val sampleRate: Int,
         val numberOfChannels: Int,
+        /**
+         * Publisher-side cadence hint (ms). hang.js's watcher uses
+         * this to size its jitter buffer — emit a real value rather
+         * than relying on the watcher's fallback default. For Opus
+         * this is the codec frame duration (20 ms at 48 kHz / 960
+         * samples) and matches what hang.js's encoder emits at
+         * `js/publish/src/audio/encoder.ts:#runConfig`.
+         */
+        val jitter: Int,
     )
 
     @Serializable
@@ -124,9 +134,20 @@ internal data class MoqLiteHangCatalog(
                                         container = Container(kind = "legacy"),
                                         sampleRate = 48_000,
                                         numberOfChannels = 1,
+                                        jitter = OPUS_FRAME_DURATION_MS,
                                     ),
                             ),
                     ),
             )
+
+        /**
+         * Opus frame duration in milliseconds — 960 samples / 48 kHz =
+         * 20 ms. Matches
+         * [com.vitorpamplona.nestsclient.audio.Audio.FRAME_SIZE_SAMPLES].
+         * Published as the catalog `jitter` hint so hang.js's watcher
+         * sizes its jitter buffer to one Opus frame, the natural
+         * cadence of our encoder.
+         */
+        private const val OPUS_FRAME_DURATION_MS: Int = 20
     }
 }

nestsClient/src/commonTest/kotlin/com/vitorpamplona/nestsclient/moq/lite/MoqLiteHangCatalogTest.kt

@@ -33,7 +33,7 @@ class MoqLiteHangCatalogTest {
         val expected =
             "{\"audio\":{\"renditions\":{\"audio/data\":{" +
                 "\"codec\":\"opus\",\"container\":{\"kind\":\"legacy\"}," +
-                "\"sampleRate\":48000,\"numberOfChannels\":1}}}}"
+                "\"sampleRate\":48000,\"numberOfChannels\":1,\"jitter\":20}}}}"
         val actual =
             MoqLiteHangCatalog.opusMono48k("audio/data").encodeJsonBytes().decodeToString()
         assertEquals(expected, actual)