test(playback): pure sleep-timer math + controller uses it

Extracts deadline/remaining/expiry into SleepTimer with unit tests (arm,
disarm, countdown clamp, expiry) so the M10 sleep timer is directly covered.

app/src/main/java/com/heretek/dorado_hd/media/PlaybackController.kt

@@ -281,9 +281,9 @@ class PlaybackController(
             cancelSleepTimer()
             return
         }
-        sleepDeadlineElapsedMs = android.os.SystemClock.elapsedRealtime() + minutes * 60_000L
+        sleepDeadlineElapsedMs = SleepTimer.deadlineMs(android.os.SystemClock.elapsedRealtime(), minutes)
         sleepActive = true
-        _sleepRemainingMs.value = minutes * 60_000L
+        _sleepRemainingMs.value = SleepTimer.remainingMs(sleepDeadlineElapsedMs, android.os.SystemClock.elapsedRealtime())
     }
 
     fun cancelSleepTimer() {
@@ -294,9 +294,9 @@ class PlaybackController(
 
     private fun tickSleepTimer(player: MediaController) {
         if (!sleepActive) return
-        val remaining = (sleepDeadlineElapsedMs - android.os.SystemClock.elapsedRealtime()).coerceAtLeast(0L)
+        val remaining = SleepTimer.remainingMs(sleepDeadlineElapsedMs, android.os.SystemClock.elapsedRealtime())
         _sleepRemainingMs.value = remaining
-        if (remaining > 0L) return
+        if (!SleepTimer.expired(sleepDeadlineElapsedMs, android.os.SystemClock.elapsedRealtime())) return
         sleepActive = false
         // Fade out over a short window, then stop; restore volume for the
         // next manual play.

app/src/main/java/com/heretek/dorado_hd/media/SleepTimer.kt

@@ -0,0 +1,22 @@
+package com.heretek.dorado_hd.media
+
+/**
+ * Pure sleep-timer math (post-device extension, canon §10). Kept free of
+ * Android so arming/expiry is unit-testable.
+ */
+object SleepTimer {
+
+    /** Deadline for [minutes] from [elapsedNowMs]; 0 or less means disarmed. */
+    fun deadlineMs(elapsedNowMs: Long, minutes: Int): Long =
+        if (minutes <= 0) 0L else elapsedNowMs + minutes * 60_000L
+
+    /** Milliseconds left, never negative. A disarmed deadline yields 0. */
+    fun remainingMs(deadlineMs: Long, elapsedNowMs: Long): Long {
+        if (deadlineMs <= 0L) return 0L
+        return (deadlineMs - elapsedNowMs).coerceAtLeast(0L)
+    }
+
+    /** True once the deadline has passed (disarmed deadlines never expire). */
+    fun expired(deadlineMs: Long, elapsedNowMs: Long): Boolean =
+        deadlineMs > 0L && elapsedNowMs >= deadlineMs
+}

app/src/test/java/com/heretek/dorado_hd/SleepTimerTest.kt

@@ -0,0 +1,36 @@
+package com.heretek.dorado_hd
+
+import com.heretek.dorado_hd.media.SleepTimer
+import org.junit.Assert.assertEquals
+import org.junit.Assert.assertFalse
+import org.junit.Assert.assertTrue
+import org.junit.Test
+
+class SleepTimerTest {
+
+    @Test
+    fun `minutes arm a deadline and non-positive values disarm`() {
+        assertEquals(30 * 60_000L, SleepTimer.deadlineMs(0L, 30))
+        assertEquals(1_000L + 15 * 60_000L, SleepTimer.deadlineMs(1_000L, 15))
+        assertEquals(0L, SleepTimer.deadlineMs(1_000L, 0))
+        assertEquals(0L, SleepTimer.deadlineMs(1_000L, -5))
+    }
+
+    @Test
+    fun `remaining counts down and never goes negative`() {
+        val deadline = SleepTimer.deadlineMs(0L, 2)
+        assertEquals(120_000L, SleepTimer.remainingMs(deadline, 0L))
+        assertEquals(60_000L, SleepTimer.remainingMs(deadline, 60_000L))
+        assertEquals(0L, SleepTimer.remainingMs(deadline, 200_000L))
+        assertEquals(0L, SleepTimer.remainingMs(0L, 5L))
+    }
+
+    @Test
+    fun `expiry fires at the deadline and never when disarmed`() {
+        val deadline = SleepTimer.deadlineMs(10_000L, 1)
+        assertFalse(SleepTimer.expired(deadline, 69_999L))
+        assertTrue(SleepTimer.expired(deadline, 70_000L))
+        assertTrue(SleepTimer.expired(deadline, 99_000L))
+        assertFalse(SleepTimer.expired(0L, Long.MAX_VALUE))
+    }
+}