Fix scrollbar bounds and loading-state stop button behavior.

Prevents VerticalScrollbar crashes on invalid coerceIn ranges and makes stop/loading UI react immediately while preserving Mistral 429 fallback retries.

Author: Android-PowerUser

app/src/main/kotlin/com/google/ai/sample/feature/multimodal/PhotoReasoningScreen.kt

@@ -506,9 +506,10 @@ fun PhotoReasoningScreen(
         }
 
         val isGemma = modelName == "gemma-3n-e4b-it"
-        val showStopButton = isGenerationRunning || isOfflineGpuModelLoaded || isGemma
-        val stopButtonText = if (isGenerationRunning) "Stop" else "Model Unload"
-        val showTextFieldRow = !isGenerationRunning || isInitializingOfflineModel
+        val isLoading = uiState is PhotoReasoningUiState.Loading
+        val showStopButton = isGenerationRunning || isLoading || isOfflineGpuModelLoaded || isGemma
+        val stopButtonText = if (isGenerationRunning || isLoading) "Stop" else "Model Unload"
+        val showTextFieldRow = (!isGenerationRunning && !isLoading) || isInitializingOfflineModel
 
         if (showTextFieldRow) {
             Card(modifier = Modifier.fillMaxWidth()) {
@@ -1371,19 +1372,23 @@ fun VerticalScrollbar(
 
             if (visibleItemCount >= totalItems) return@derivedStateOf null // All items visible, no scrollbar
 
-            // Simple ratio-based calculation for even behavior
-            val thumbHeight = (visibleItemCount.toFloat() / totalItems * viewportHeight).coerceAtLeast(20f)
-            
-            // Calculate scroll progress considering sub-item offset
+            val thumbHeight = (visibleItemCount.toFloat() / totalItems * viewportHeight)
+                .coerceAtLeast(20f)
+                .coerceAtMost(viewportHeight)
+
+            val maxScrollOffset = (viewportHeight - thumbHeight).coerceAtLeast(0f)
+            if (maxScrollOffset == 0f) return@derivedStateOf null
+
             val firstItemOffset = if (layoutInfo.visibleItemsInfo.isNotEmpty()) {
                 val firstItem = layoutInfo.visibleItemsInfo.first()
                 if (firstItem.size > 0) listState.firstVisibleItemScrollOffset.toFloat() / firstItem.size else 0f
             } else 0f
-            
-            val scrollProgress = (firstVisibleItemIndex + firstItemOffset) / (totalItems - visibleItemCount).coerceAtLeast(1)
-            val scrollOffset = scrollProgress * (viewportHeight - thumbHeight)
 
-            Pair(scrollOffset.coerceIn(0f, viewportHeight - thumbHeight), thumbHeight)
+            val scrollProgress = (firstVisibleItemIndex + firstItemOffset) /
+                (totalItems - visibleItemCount).coerceAtLeast(1)
+            val scrollOffset = (scrollProgress * maxScrollOffset).coerceIn(0f, maxScrollOffset)
+
+            Pair(scrollOffset, thumbHeight)
         }
     }
 

app/src/main/kotlin/com/google/ai/sample/feature/multimodal/PhotoReasoningViewModel.kt

@@ -1174,13 +1174,34 @@ private fun reasonWithMistral(
                 apiKeyManager.markKeyAsFailed(currentKey, ApiProvider.MISTRAL)
                 val nextKey = apiKeyManager.switchToNextAvailableKey(ApiProvider.MISTRAL)
                 if (nextKey != null && nextKey != currentKey) {
+                    // Anderer Key verfugbar -> sofort wechseln wie bisher
                     currentKey = nextKey
                     val elapsed2 = System.currentTimeMillis() - lastMistralRequestTimeMs
                     if (elapsed2 < MISTRAL_MIN_INTERVAL_MS) delay(MISTRAL_MIN_INTERVAL_MS - elapsed2)
                     response = client.newCall(buildRequest(currentKey)).execute()
                     lastMistralRequestTimeMs = System.currentTimeMillis()
                 } else {
-                    throw IOException("Mistral rate limit reached. Please add another API key.")
+                    // Kein anderer Key -> 5 Sekunden lang sofort wiederholen
+                    apiKeyManager.resetFailedKeys(ApiProvider.MISTRAL)
+                    withContext(Dispatchers.Main) {
+                        replaceAiMessageText("Rate limit erreicht. Wiederhole...", isPending = true)
+                    }
+                    val retryDeadline = System.currentTimeMillis() + 5000L
+                    var retryResponse: okhttp3.Response? = null
+                    while (System.currentTimeMillis() < retryDeadline) {
+                        if (stopExecutionFlag.get()) break
+                        val retryResp = client.newCall(buildRequest(currentKey)).execute()
+                        lastMistralRequestTimeMs = System.currentTimeMillis()
+                        if (retryResp.code != 429) {
+                            retryResponse = retryResp
+                            break
+                        }
+                        retryResp.close()
+                    }
+                    if (retryResponse == null || stopExecutionFlag.get()) {
+                        throw IOException("Mistral rate limit: Kein Erfolg innerhalb von 5 Sekunden.")
+                    }
+                    response = retryResponse
                 }
             }