Fix placeholder visibility in media-send.

feature/media-send/src/main/java/org/signal/mediasend/MediaSendFlowViewModel.kt

@@ -100,7 +100,7 @@ class MediaSendFlowViewModel(
     isReply = args.isReply,
     isAddToGroupStoryFlow = args.isAddToGroupStoryFlow,
     maxSelection = args.maxSelection,
-    message = if (args.asTextStory) null else args.initialMessage,
+    message = if (args.asTextStory) null else normalizeMessageBody(args.initialMessage),
     isContactSelectionRequired = args.mode == MediaSendFlowActivityContract.Mode.ChooseAfterMediaSelection,
     sendType = args.sendType
   )
@@ -1077,11 +1077,7 @@ class MediaSendFlowViewModel(
   //region Message
 
   fun setMessage(text: CharSequence?) {
-    updateState { copy(message = text) }
-  }
-
-  private fun onMessageChange(message: String) {
-    setMessage(message)
+    updateState { copy(message = normalizeMessageBody(text)) }
   }
 
   //endregion
@@ -1321,6 +1317,14 @@ class MediaSendFlowViewModel(
     private const val KEY_STATE = "media_send_vm_state"
     private const val KEY_EDITED_VIDEO_URIS = "media_send_vm_edited_video_uris"
     private const val KEY_BACK_STACK = "media_send_vm_back_stack"
+
+    /**
+     * Trims a body the way the chat compose field does before a send, preserving spans like mentions and styling, and
+     * collapses a whitespace-only body to null so it is indistinguishable from a body the user never typed.
+     */
+    private fun normalizeMessageBody(text: CharSequence?): CharSequence? {
+      return text?.let { StringUtil.trimSequence(it) }?.takeIf { it.isNotEmpty() }
+    }
   }
 
   /**

feature/media-send/src/main/java/org/signal/mediasend/screens/edit/AddAMessageRow.kt

@@ -113,7 +113,7 @@ fun AddAMessageRow(
         }
 
         LocalAddAMessageRowTextField.current(
-          message ?: stringResource(R.string.AddAMessageRow__message),
+          message?.takeIf { it.isNotBlank() } ?: stringResource(R.string.AddAMessageRow__message),
           Modifier
             .weight(1f)
             .padding(end = if (viewOnceAvailable) 0.dp else 16.dp)

feature/media-send/src/test/java/org/signal/mediasend/screens/edit/AddAMessageRowTest.kt

@@ -9,6 +9,7 @@ import android.app.Application
 import androidx.compose.ui.test.junit4.createComposeRule
 import androidx.compose.ui.test.longClick
 import androidx.compose.ui.test.onNodeWithTag
+import androidx.compose.ui.test.onNodeWithText
 import androidx.compose.ui.test.performClick
 import androidx.compose.ui.test.performTouchInput
 import androidx.test.core.app.ApplicationProvider
@@ -25,7 +26,7 @@ import org.signal.mediasend.test.TestTags
 
 /**
  * Covers the send affordance's two gestures: a tap advances the flow, while a long press offers the schedule menu when
- * the flow allows scheduling.
+ * the flow allows scheduling. Also covers when the row falls back to its placeholder.
  */
 @RunWith(RobolectricTestRunner::class)
 @Config(application = Application::class)
@@ -74,11 +75,25 @@ class AddAMessageRowTest {
     assertEquals(emptyList<MediaEditScreenEvents>(), events)
   }
 
-  private fun setContent(canScheduleSend: Boolean) {
+  @Test
+  fun `Given a blank message, when the row is displayed, then the placeholder is shown`() {
+    setContent(message = "   ")
+
+    composeTestRule.onNodeWithText("Message").assertExists()
+  }
+
+  @Test
+  fun `Given a message, when the row is displayed, then the message is shown`() {
+    setContent(message = "Check this out")
+
+    composeTestRule.onNodeWithText("Check this out").assertExists()
+  }
+
+  private fun setContent(canScheduleSend: Boolean = false, message: CharSequence? = null) {
     composeTestRule.setContent {
       SignalTheme {
         AddAMessageRow(
-          message = null,
+          message = message,
           onEvent = { events += it },
           onNextClick = { nextClicks++ },
           canScheduleSend = canScheduleSend