fix: Correct system message TextField behavior

Addresses your feedback on the system message TextField in PhotoReasoningScreen:

- Sets focused height with keyboard to 450dp (was 600dp).
- Dynamically adjusts minLines and maxLines of the OutlinedTextField to ensure the text input area expands with the component's height.
- Modifies the BackHandler to explicitly clear focus from the TextField (in addition to collapsing it) when it's focused without the keyboard and back is pressed. This ensures it can be re-expanded correctly on subsequent focus.

These changes improve the usability and appearance of the system message input field.

Author: google-labs-jules[bot]

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

@@ -54,6 +54,7 @@ import androidx.compose.ui.focus.onFocusChanged
 import androidx.compose.ui.draw.drawBehind
 import androidx.compose.ui.graphics.Color
 import androidx.compose.ui.platform.LocalContext
+import androidx.compose.ui.platform.LocalFocusManager
 import androidx.compose.ui.res.stringResource
 import androidx.compose.ui.tooling.preview.Preview
 import androidx.compose.ui.unit.dp
@@ -195,9 +196,11 @@ fun PhotoReasoningScreen(
     var isSystemMessageFocused by rememberSaveable { mutableStateOf(false) }
     val listState = rememberLazyListState()
     val context = LocalContext.current // Get context for Toast
+    val focusManager = LocalFocusManager.current
 
     BackHandler(enabled = isSystemMessageFocused && !isKeyboardOpen) {
-        isSystemMessageFocused = false
+        focusManager.clearFocus() // Clear focus first
+        isSystemMessageFocused = false // Then update the state that controls height
     }
 
     val pickMedia = rememberLauncherForActivityResult(
@@ -234,10 +237,12 @@ fun PhotoReasoningScreen(
                 )
                 Spacer(modifier = Modifier.height(8.dp))
                 val systemMessageHeight = when {
-                    isSystemMessageFocused && isKeyboardOpen -> 600.dp
+                    isSystemMessageFocused && isKeyboardOpen -> 450.dp // Changed from 600.dp
                     isSystemMessageFocused && !isKeyboardOpen -> 1000.dp
                     else -> 120.dp
                 }
+                val currentMinLines = if (systemMessageHeight == 120.dp) 3 else 1
+                val currentMaxLines = if (systemMessageHeight == 120.dp) 5 else Int.MAX_VALUE
                 OutlinedTextField(
                     value = systemMessage,
                     onValueChange = onSystemMessageChanged,
@@ -246,8 +251,8 @@ fun PhotoReasoningScreen(
                         .fillMaxWidth()
                         .height(systemMessageHeight)
                         .onFocusChanged { focusState -> isSystemMessageFocused = focusState.isFocused },
-                    maxLines = 5,
-                    minLines = 3
+                    minLines = currentMinLines,
+                    maxLines = currentMaxLines
                 )
             }
         }