Add tested adaptive playback device buffer policy

tools/chatgui-android/app/src/main/java/com/utun/chat/data/CallPlaybackBuffer.kt

@@ -0,0 +1,68 @@
+package com.utun.chat.data
+
+/** Запас устройства, не сетевой JB. Владелец сериализует sample/applied/settle одним lock. */
+internal class CallPlaybackBuffer(val blockFrames: Int = 960) {
+    data class Change(val frames: Int, val reason: String, val underruns: Int = 0)
+
+    private var actual = 0
+    private var capacity = 0
+    private var floor = blockFrames
+    private var previousUnderruns = 0
+    private var previousPlayed = -1L
+    private var previousMs = 0L
+    private var stableSinceMs = 0L
+    private var settleUntilMs = 0L
+    private var probeIntervalMs = 30_000L
+
+    fun reset(nowMs: Long, frames: Int, capacityFrames: Int, underruns: Int) {
+        require(frames > 0 && capacityFrames >= frames && underruns >= 0)
+        actual = frames
+        capacity = capacityFrames
+        floor = blockFrames
+        previousUnderruns = underruns
+        previousPlayed = -1
+        previousMs = nowMs
+        probeIntervalMs = 30_000
+        settle(nowMs)
+    }
+
+    /** Старт и запрос/подтверждение маршрута не участвуют в обучении. */
+    fun settle(nowMs: Long) {
+        settleUntilMs = nowMs + 2_000
+        stableSinceMs = settleUntilMs
+    }
+
+    fun sample(nowMs: Long, underruns: Int, played: Long): Change? {
+        val delta = underruns - previousUnderruns
+        val progress = played >= 0 && previousPlayed >= 0 && played > previousPlayed
+        val timely = nowMs - previousMs in 1..1_000
+        previousUnderruns = underruns
+        previousPlayed = played
+        previousMs = nowMs
+        if (nowMs < settleUntilMs) return null
+        if (delta < 0) {
+            settle(nowMs)
+            return Change(actual, "counter-reset")
+        }
+        if (delta > 0) {
+            probeIntervalMs = (probeIntervalMs * 2).coerceAtMost(300_000)
+            settle(nowMs)
+            val next = (actual + blockFrames).coerceAtMost(capacity)
+            if (next == actual) settleUntilMs = nowMs + 10_000
+            return Change(next, if (next > actual) "underrun" else "capacity-limit", delta)
+        }
+        if (!progress || !timely) stableSinceMs = nowMs
+        if (actual <= floor || nowMs - stableSinceMs < probeIntervalMs) return null
+        stableSinceMs = nowMs
+        return Change((actual - blockFrames).coerceAtLeast(floor), "stable-probe")
+    }
+
+    /** Устройство может округлить/ограничить заявку: учимся по принятому размеру. */
+    fun applied(nowMs: Long, change: Change, frames: Int, capacityFrames: Int) {
+        require(frames > 0 && capacityFrames >= frames)
+        if (change.frames < actual && frames >= actual) floor = frames
+        actual = frames
+        capacity = capacityFrames
+        settle(nowMs)
+    }
+}