refine: AOS binary-search refinement, getRadios signature cleanup

Refine AOS crossing to ~500ms via binary search instead of linear stepping; simplify getRadios to take satPos; tidy radar view/viewmodel.

core/data/src/main/java/com/rtbishop/look4sat/core/data/repository/SatelliteRepo.kt

@@ -95,14 +95,8 @@ class SatelliteRepo(
         }
     }
 
-    override suspend fun getRadios(
-        sat: OrbitalObject,
-        pos: GeoPos,
-        radios: List<SatRadio>,
-        time: Long
-    ): List<SatRadio> {
+    override suspend fun getRadios(satPos: OrbitalPos, radios: List<SatRadio>): List<SatRadio> {
         return withContext(dispatcher) {
-            val satPos = sat.getPosition(pos, time)
             radios.map { transmitter ->
                 transmitter.copy(
                     downlinkLow = transmitter.downlinkLow?.let { satPos.getDownlinkFreq(it) },
@@ -242,13 +236,16 @@ class SatelliteRepo(
             if (elevation > maxElevation) maxElevation = elevation
         } while (elevation < 0.0)
 
-        // refine AOS to ~500ms precision
-        calendarTimeMillis -= 60L * 1000L
-        do {
-            calendarTimeMillis += 500L
-            elevation = sat.getElevation(pos, calendarTimeMillis)
-            if (elevation > maxElevation) maxElevation = elevation
-        } while (elevation < 0.0)
+        // refine AOS to ~500ms precision via binary search.
+        // Elevation is monotonic across the horizon crossing, so binary search
+        // finds the crossing in ~8 SGP4 calls instead of up to 120 linear steps.
+        var aosLo = calendarTimeMillis - 60L * 1000L // elevation < 0 (below horizon)
+        var aosHi = calendarTimeMillis // elevation >= 0 (above horizon)
+        while (aosHi - aosLo > 500L) {
+            val mid = (aosLo + aosHi) / 2
+            if (sat.getElevation(pos, mid) < 0.0) aosLo = mid else aosHi = mid
+        }
+        calendarTimeMillis = aosHi
 
         // Get full position for AOS data (azimuth, altitude)
         val aosPos = sat.getFullPosition(pos, calendarTimeMillis)
@@ -262,13 +259,14 @@ class SatelliteRepo(
             if (elevation > maxElevation) maxElevation = elevation
         } while (elevation > 0.0)
 
-        // refine LOS to ~500ms precision
-        calendarTimeMillis -= 30L * 1000L
-        do {
-            calendarTimeMillis += 500L
-            elevation = sat.getElevation(pos, calendarTimeMillis)
-            if (elevation > maxElevation) maxElevation = elevation
-        } while (elevation > 0.0)
+        // refine LOS to ~500ms precision via binary search (same monotonic argument)
+        var losLo = calendarTimeMillis - 30L * 1000L // elevation > 0 (above horizon)
+        var losHi = calendarTimeMillis // elevation <= 0 (below horizon)
+        while (losHi - losLo > 500L) {
+            val mid = (losLo + losHi) / 2
+            if (sat.getElevation(pos, mid) > 0.0) losLo = mid else losHi = mid
+        }
+        calendarTimeMillis = losHi
 
         // Get full position for LOS data (azimuth, altitude)
         val losPos = sat.getFullPosition(pos, calendarTimeMillis)

core/domain/src/main/java/com/rtbishop/look4sat/core/domain/repository/ISatelliteRepo.kt

@@ -61,7 +61,7 @@ interface ISatelliteRepo {
     suspend fun getTrack(sat: OrbitalObject, pos: GeoPos, start: Long, end: Long): List<OrbitalPos>
 
     /** Get Doppler-shifted radio frequencies for a satellite at the given time. */
-    suspend fun getRadios(sat: OrbitalObject, pos: GeoPos, radios: List<SatRadio>, time: Long): List<SatRadio>
+    suspend fun getRadios(satPos: OrbitalPos, radios: List<SatRadio>): List<SatRadio>
 
     /** Fetch radio transceivers for a satellite by its catalog number. */
     suspend fun getRadiosWithId(id: Int): List<SatRadio>

feature/radar/src/main/java/com/rtbishop/look4sat/feature/radar/RadarView.kt

@@ -94,14 +94,21 @@ fun RadarViewCompose(
         animationSpec = infiniteRepeatable(tween(1000)),
         label = "animScale"
     )
-    // Drive the sweep from the animation framework to eliminate state mutation inside the draw block
-    val sweepTransition = rememberInfiniteTransition(label = "sweep")
-    val sweepDegrees by sweepTransition.animateFloat(
-        initialValue = 0f,
-        targetValue = 360f,
-        animationSpec = infiniteRepeatable(tween(SWEEP_DURATION_MS, easing = LinearEasing)),
-        label = "sweepDegrees"
-    )
+    // Drive the sweep from the animation framework to eliminate state mutation inside the draw block.
+    // Only create the infinite transition when the sweep is enabled — otherwise the canvas would
+    // be invalidated every frame for an effect that isn't visible, wasting GPU and battery.
+    val sweepDegrees: Float
+    if (shouldShowSweep) {
+        val sweepTransition = rememberInfiniteTransition(label = "sweep")
+        sweepDegrees by sweepTransition.animateFloat(
+            initialValue = 0f,
+            targetValue = 360f,
+            animationSpec = infiniteRepeatable(tween(SWEEP_DURATION_MS, easing = LinearEasing)),
+            label = "sweepDegrees"
+        )
+    } else {
+        sweepDegrees = 0f
+    }
     val measurer = rememberTextMeasurer()
     val sunPainter = painterResource(R.drawable.ic_sun)
     val moonPainter = painterResource(R.drawable.ic_moon)

feature/radar/src/main/java/com/rtbishop/look4sat/feature/radar/RadarViewModel.kt

@@ -181,7 +181,7 @@ class RadarViewModel(
                 orbitalPos = pos, sunPosition = cachedSunPos, moonPosition = cachedMoonPos
             )
         }
-        processRadios(allRadios, pass.orbitalObject, timeNow)
+        processRadios(allRadios, pos)
         sendPassData(pos)
     }
 
@@ -342,8 +342,8 @@ class RadarViewModel(
         }
     }
 
-    private suspend fun processRadios(radios: List<SatRadio>, orbitalObject: OrbitalObject, time: Long) {
-        val transmitters = satelliteRepo.getRadios(orbitalObject, stationPos, radios, time)
+    private suspend fun processRadios(radios: List<SatRadio>, satPos: OrbitalPos) {
+        val transmitters = satelliteRepo.getRadios(satPos, radios)
         _uiState.update { state ->
             val freq = if (state.transceivers.selectedUuid != null) {
                 val selectedRadio = transmitters.firstOrNull { it.uuid == state.transceivers.selectedUuid }