Log simulator starts, stops and diagnostics to a file on the tablet

The Mavic Pro simulator closes by itself every 3-11 minutes and logcat on the
dev tablet rolls over before it can be read. SimLog appends the simulator's
on/off changes (with the flight state at that moment), the app's own start
and stop commands, and every diagnostics change to files/sim_log.txt.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

Fly App/android/app/src/main/kotlin/com/pilotvault/flyapp/DiagnosticsBridge.kt

@@ -33,6 +33,7 @@ class DiagnosticsBridge(private val ctx: BridgeCtx) : SubBridge {
                 ctx.mainHandler.post {
                     if (items == last) return@post
                     last = items
+                    SimLog.write(ctx.appContext, "diagnostics: " + items.joinToString(" | ") { "${it["code"]} ${it["reason"]}" })
                     ctx.emit(mapOf("type" to "diagnostics", "items" to items))
                 }
             }

Fly App/android/app/src/main/kotlin/com/pilotvault/flyapp/FlightControllerBridge.kt

@@ -25,6 +25,9 @@ import kotlin.math.sqrt
  */
 class FlightControllerBridge(private val ctx: BridgeCtx) : SubBridge {
 
+    /** The simulator state last seen, so [SimLog] records only its changes. */
+    @Volatile private var lastSimulatorActive: Boolean? = null
+
     private fun fc(): FlightController? = ctx.aircraft()?.flightController
 
     override fun handle(call: MethodCall, result: MethodChannel.Result): Boolean {
@@ -58,10 +61,12 @@ class FlightControllerBridge(private val ctx: BridgeCtx) : SubBridge {
                         call.argument<Int>("updateFrequency") ?: 10,
                         call.argument<Int>("satelliteCount") ?: 12,
                     )
+                    SimLog.write(ctx.appContext, "app: startSimulator")
                     sim.start(data, ctx.completion(result))
                 }
             }
             "stopSimulator" -> guard(controller, result) {
+                SimLog.write(ctx.appContext, "app: stopSimulator")
                 val sim = it.simulator
                 if (sim == null) ctx.fail(result, "Simulator unavailable on this aircraft")
                 else sim.stop(ctx.completion(result))
@@ -135,8 +140,19 @@ class FlightControllerBridge(private val ctx: BridgeCtx) : SubBridge {
         if (product !is Aircraft) return
         val controller = product.flightController ?: return
         controller.setStateCallback { state ->
-            val values = telemetry(state) + compass(controller) +
-                ("simulatorActive" to (try { controller.simulator?.isSimulatorActive } catch (_: Throwable) { null }))
+            val sim = try { controller.simulator?.isSimulatorActive } catch (_: Throwable) { null }
+            if (sim != null && sim != lastSimulatorActive) {
+                if (lastSimulatorActive != null || sim) {
+                    SimLog.write(
+                        ctx.appContext,
+                        "simulator ${if (sim) "ON" else "OFF"}: mode=${state.flightModeString} flying=${state.isFlying} " +
+                            "motors=${state.areMotorsOn()} alt=${state.aircraftLocation?.altitude} sats=${state.satelliteCount} " +
+                            "flightTime=${state.flightTimeInSeconds}s goHome=${state.goHomeExecutionState}",
+                    )
+                }
+                lastSimulatorActive = sim
+            }
+            val values = telemetry(state) + compass(controller) + ("simulatorActive" to sim)
             ctx.mainHandler.post { ctx.hub.putFast(values) }
         }
         // Magnetic interference per compass (P6b's interference meter): the

Fly App/android/app/src/main/kotlin/com/pilotvault/flyapp/SimLog.kt

@@ -0,0 +1,32 @@
+package com.pilotvault.flyapp
+
+import android.content.Context
+import android.util.Log
+import java.io.File
+import java.text.SimpleDateFormat
+import java.util.Date
+import java.util.Locale
+
+/**
+ * A small file log for the simulator closing by itself (Mavic Pro, every
+ * 3–11 min, cause unknown): simulator starts/stops with the flight state at
+ * that moment, and every diagnostics change. logcat on the dev tablet rolls
+ * over within minutes, so this lives in the app's files dir (`sim_log.txt`,
+ * capped at [MAX_BYTES]) and is read with `run-as … cat files/sim_log.txt`.
+ */
+object SimLog {
+    private const val FILE = "sim_log.txt"
+    private const val MAX_BYTES = 512 * 1024
+    private val time = SimpleDateFormat("yyyy-MM-dd HH:mm:ss.SSS", Locale.ROOT)
+
+    fun write(context: Context, line: String) {
+        Log.w("PVSim", line)
+        try {
+            val f = File(context.filesDir, FILE)
+            if (f.length() > MAX_BYTES) f.delete()
+            synchronized(this) { f.appendText("${time.format(Date())} $line\n") }
+        } catch (_: Throwable) {
+            // Logging must never break a flight.
+        }
+    }
+}