fix(android): keep inverted chat still during text selection

React Native decomposes Android list inversion into a 180-degree rotation with positive scaleY, so the existing visibility-scroll guard never recognized the inverted viewport. Inspect the composed matrix and reproduce the actual list transform through the native view manager in regression tests.

docs/native-text-selection.md

@@ -2,6 +2,15 @@
 
 Keep assistant prose in one native text view so selection crosses paragraphs, headings and lists. The shared [Markdown renderer](markdown-renderer.md) owns that view.
 
+## Android inverted chat
+
+Keep selection visibility handling in `modules/paseo-scroll`. Android's visibility
+rectangles ignore list inversion. React Native decomposes Android's `scale: -1`
+into rotation with positive `scaleY`, so test the composed matrix when deciding
+whether those requests should move the viewport. Native tests must apply the
+list's transform through React Native's view manager; assigning `scaleY` directly
+misses that decomposition.
+
 ## Diagrams in lists and quotes
 
 Selection stops at a Mermaid diagram. Native extracts Mermaid fences into separate views because the library exposes no native block renderer override. A diagram inside a list or quote therefore appears outside that container, and its following prose starts a separate Markdown fragment.

packages/app/modules/paseo-scroll/android/src/androidTest/java/sh/paseo/scroll/ScrollSelectionTest.kt

@@ -8,6 +8,9 @@ import android.widget.FrameLayout
 import android.widget.TextView
 import androidx.test.ext.junit.runners.AndroidJUnit4
 import androidx.test.platform.app.InstrumentationRegistry
+import com.facebook.react.bridge.JavaOnlyArray
+import com.facebook.react.bridge.JavaOnlyMap
+import com.facebook.react.uimanager.ReactStylesDiffMap
 import com.facebook.react.bridge.BridgeReactContext
 import com.facebook.react.soloader.OpenSourceMergedSoMapping
 import com.facebook.react.uimanager.ThemedReactContext
@@ -47,16 +50,34 @@ class ScrollSelectionTest {
     assertNotEquals(before, scroll.scrollY)
   }
 
+  @Test fun directVerticalMirroringKeepsSelectionStill() = withScroll(inverted = false) { scroll, text ->
+    scroll.scaleY = -1f
+    val before = scroll.scrollY
+    text.requestRectangleOnScreen(Rect(0, 0, 80, 40), true)
+    assertEquals(before, scroll.scrollY)
+  }
+
+  @Test fun horizontalMirroringStillRevealsSelectedText() = withScroll(inverted = false) { scroll, text ->
+    scroll.scaleX = -1f
+    val before = scroll.scrollY
+    text.requestRectangleOnScreen(Rect(0, 0, 80, 40), true)
+    assertNotEquals(before, scroll.scrollY)
+  }
+
   private fun withScroll(inverted: Boolean, check: (ReactScrollView, TextView) -> Unit) {
     val instrumentation = InstrumentationRegistry.getInstrumentation()
     instrumentation.runOnMainSync {
       val appContext = instrumentation.targetContext
       SoLoader.init(appContext, OpenSourceMergedSoMapping)
+      com.facebook.react.uimanager.DisplayMetricsHolder.initDisplayMetricsIfNotInitialized(appContext)
       val reactContext = BridgeReactContext(appContext)
       val context = ThemedReactContext(reactContext, appContext)
       val manager = PaseoScrollPackage().createViewManager(reactContext, ReactScrollViewManager.REACT_CLASS) as ReactScrollViewManager
       val scroll = manager.createViewInstance(context)
-      scroll.scaleY = if (inverted) -1f else 1f
+      // Exercise VirtualizedList's Android transform through RN's real decomposition.
+      if (inverted) manager.updateProperties(scroll, ReactStylesDiffMap(JavaOnlyMap.of(
+        "transform", JavaOnlyArray.of(JavaOnlyMap.of("scale", -1.0))
+      )))
       val content = FrameLayout(context)
       val text = TextView(context).apply {
         setText("Selectable timeline text", TextView.BufferType.SPANNABLE)

packages/app/modules/paseo-scroll/android/src/main/java/sh/paseo/scroll/PaseoScrollPackage.kt

@@ -1,5 +1,6 @@
 package sh.paseo.scroll
 
+import android.graphics.Matrix
 import android.graphics.Rect
 import com.facebook.react.ReactPackage
 import com.facebook.react.ViewManagerOnDemandReactPackage
@@ -27,9 +28,15 @@ private class PaseoScrollViewManager : ReactScrollViewManager() {
 }
 
 private class PaseoScrollView(context: ThemedReactContext) : ReactScrollView(context) {
-  // Both RN focus handling and Android selection visibility requests use this calculation.
-  // Its coordinates ignore inversion. Keep focus/selection bookkeeping, but leave timeline
-  // movement to user gestures and explicit scroll commands.
-  override fun computeScrollDeltaToGetChildRectOnScreen(rect: Rect): Int =
-    if (scaleY < 0) 0 else super.computeScrollDeltaToGetChildRectOnScreen(rect)
+  private val transformValues = FloatArray(9)
+
+  // Android VirtualizedList uses scale: -1, which RN decomposes into a 180-degree
+  // rotation with positive scaleY. Inspect the composed transform so both that
+  // inversion and a direct scaleY: -1 suppress untransformed visibility requests.
+  // Keep focus/selection bookkeeping; gestures and explicit commands still scroll.
+  override fun computeScrollDeltaToGetChildRectOnScreen(rect: Rect): Int {
+    matrix.getValues(transformValues)
+    return if (transformValues[Matrix.MSCALE_Y] < 0) 0
+      else super.computeScrollDeltaToGetChildRectOnScreen(rect)
+  }
 }