Do not enlarge images on open

PLAN.md

@@ -1048,7 +1048,8 @@ dev-updater (Kotlin 2.4.x, CMP 1.11.x, JDK 21).
      system-bar regions** (2026-09-12). It hides the status and navigation bars
      independently when the fitted, zoomed or panned image reaches them, and
      restores either one when it does not. `100%` recenters at one bitmap pixel
-     per screen pixel; opening still fits the whole image first.
+     per screen pixel; opening only shrinks an image that needs it to fit and
+     never enlarges a smaller one.
    - **All transcript text is selectable, from one `SelectionContainer`
      around the whole list.** Not per row: a transcript is one body of text,
      so a selection has to run from a reply into the tool output under it —

app/androidApp/src/main/kotlin/com/example/aiapp/SessionImage.kt

@@ -292,7 +292,8 @@ private fun enlargingFilter(sourceHeight: Int, drawnHeight: Int): FilterQuality
  *
  * Inside a dialog rather than a screen -- see [SessionImageViewer] -- so the platform's back
  * gesture returns to the transcript instead of leaving the app. It opens fitted, with the whole
- * image visible; the 100% control changes to one bitmap pixel per screen pixel and recenters it.
+ * image visible without enlarging a smaller one; the 100% control changes to one bitmap pixel per
+ * screen pixel and recenters it.
  */
 @Composable
 private fun ZoomableImage(
@@ -328,7 +329,7 @@ private fun ZoomableImage(
     Image(
         bitmap = image,
         contentDescription = "Attached image",
-        contentScale = ContentScale.Fit,
+        contentScale = ContentScale.Inside,
         // Zoomed in, the reader is looking at pixels on purpose.
         filterQuality = FilterQuality.None,
         modifier =
@@ -337,9 +338,8 @@ private fun ZoomableImage(
                 .pointerInput(nativeScale) {
                     detectTransformGestures { centroid, pan, zoom, _ ->
                         val oldScale = scale
-                        val minimumScale = minOf(1f, nativeScale)
                         val maximumScale = maxOf(8f, nativeScale)
-                        val newScale = (oldScale * zoom).coerceIn(minimumScale, maximumScale)
+                        val newScale = (oldScale * zoom).coerceIn(1f, maximumScale)
                         if (newScale > 1f) {
                             val offset =
                                 zoomOffset(
@@ -414,8 +414,7 @@ internal fun viewerBars(
     if (imageWidth <= 0 || imageHeight <= 0 || viewportWidth <= 0 || viewportHeight <= 0) {
         return ViewerBars()
     }
-    val fittedScale =
-        minOf(viewportWidth.toFloat() / imageWidth, viewportHeight.toFloat() / imageHeight)
+    val fittedScale = insideScale(imageWidth, imageHeight, viewportWidth, viewportHeight)
     val width = imageWidth * fittedScale * scale
     val height = imageHeight * fittedScale * scale
     val left = viewportWidth / 2f + offset.x - width / 2f
@@ -433,7 +432,7 @@ internal fun viewerBars(
     )
 }
 
-/** Scale relative to [ContentScale.Fit] at which bitmap and screen pixels are one-to-one. */
+/** Scale relative to [ContentScale.Inside] at which bitmap and screen pixels are one-to-one. */
 internal fun nativeScale(
     imageWidth: Int,
     imageHeight: Int,
@@ -441,11 +440,22 @@ internal fun nativeScale(
     viewportHeight: Int,
 ): Float {
     if (imageWidth <= 0 || imageHeight <= 0 || viewportWidth <= 0 || viewportHeight <= 0) return 1f
-    val fittedScale =
-        minOf(viewportWidth.toFloat() / imageWidth, viewportHeight.toFloat() / imageHeight)
-    return 1f / fittedScale
+    return 1f / insideScale(imageWidth, imageHeight, viewportWidth, viewportHeight)
 }
 
+/** The downscale-only factor used by [ContentScale.Inside]. */
+private fun insideScale(
+    imageWidth: Int,
+    imageHeight: Int,
+    viewportWidth: Int,
+    viewportHeight: Int,
+): Float =
+    minOf(
+        1f,
+        viewportWidth.toFloat() / imageWidth,
+        viewportHeight.toFloat() / imageHeight,
+    )
+
 /** Keeps the image point beneath [centroid] beneath the fingers as its scale changes. */
 internal fun zoomOffset(
     offset: Offset,

app/androidApp/src/test/kotlin/com/example/aiapp/SessionImageTest.kt

@@ -10,8 +10,8 @@ class SessionImageTest {
         assertEquals(
             ViewerBars(status = true, navigation = true),
             viewerBars(
-                imageWidth = 500,
-                imageHeight = 1000,
+                imageWidth = 1000,
+                imageHeight = 2000,
                 viewportWidth = 1000,
                 viewportHeight = 2000,
                 scale = 1f,
@@ -67,9 +67,9 @@ class SessionImageTest {
     }
 
     @Test
-    fun `native scale reverses enlarging a small image`() {
+    fun `native scale leaves a small image alone`() {
         assertEquals(
-            0.5f,
+            1f,
             nativeScale(
                 imageWidth = 500,
                 imageHeight = 500,