Preserve the selected flash mode across camera rebinds.

feature/camera/src/main/java/org/signal/camera/CameraScreenViewModel.kt

@@ -531,10 +531,15 @@ class CameraScreenViewModel : ViewModel() {
       .build()
       .also { it.surfaceProvider = event.surfaceProvider }
 
-    // Image capture with 16:9 aspect ratio (optimized for speed)
+    // Image capture with 16:9 aspect ratio (optimized for speed).
+    // The flash mode must be seeded from state: this builds a brand new ImageCapture, and a fresh one
+    // defaults to FLASH_MODE_OFF. Rebinds happen on every camera switch and every re-entry into the
+    // camera, so without this the HUD would keep showing the user's flash selection while the hardware
+    // flash silently stopped firing.
     val imageCapture = ImageCapture.Builder()
       .setCaptureMode(ImageCapture.CAPTURE_MODE_MINIMIZE_LATENCY)
       .setResolutionSelector(resolutionSelector)
+      .setFlashMode(_state.value.flashMode.cameraxMode)
       .build()
 
     val videoCapture: VideoCapture<Recorder>? = if (event.captureMode == CameraCaptureMode.ImageAndVideoSimultaneous && !FORCE_LIMITED_BINDING) {

feature/camera/src/test/java/org/signal/camera/CameraScreenViewModelTest.kt

@@ -11,6 +11,7 @@ import androidx.camera.core.CameraControl
 import androidx.camera.core.CameraInfo
 import androidx.camera.core.CameraSelector
 import androidx.camera.core.ImageAnalysis
+import androidx.camera.core.ImageCapture
 import androidx.camera.core.Preview
 import androidx.camera.core.ZoomState
 import androidx.camera.lifecycle.ProcessCameraProvider
@@ -135,6 +136,7 @@ class CameraScreenViewModelTest {
 
   private fun List<Any?>.hasVideoCapture() = any { it is VideoCapture<*> }
   private fun List<Any?>.hasImageAnalysis() = any { it is ImageAnalysis }
+  private fun List<Any?>.imageCapture() = filterIsInstance<ImageCapture>().firstOrNull()
 
   private fun setupZoomState(minZoom: Float, maxZoom: Float) {
     val mockZoomState: ZoomState = mockk()
@@ -340,6 +342,26 @@ class CameraScreenViewModelTest {
     assertThat(viewModel.state.value.flashMode).isEqualTo(FlashMode.Off)
   }
 
+  @Test
+  fun `rebinding after the flash mode was set carries that flash mode onto the new ImageCapture`() {
+    bindCamera()
+    viewModel.onEvent(CameraScreenEvents.SetFlashMode(FlashMode.On))
+
+    // A camera switch or a re-entry into the camera rebinds, building a brand new ImageCapture.
+    val attempts = captureBindingAttempts()
+    bindCamera()
+
+    assertThat(attempts.last().imageCapture()?.flashMode).isEqualTo(ImageCapture.FLASH_MODE_ON)
+  }
+
+  @Test
+  fun `binding with the default flash mode leaves the ImageCapture flash off`() {
+    val attempts = captureBindingAttempts()
+    bindCamera()
+
+    assertThat(attempts.last().imageCapture()?.flashMode).isEqualTo(ImageCapture.FLASH_MODE_OFF)
+  }
+
   // ===========================================================================
   // Camera switching
   // ===========================================================================