feat(chats): always show attach button, auto-force NIP-17 with snackbar

- Attach button always visible in DM input (not gated on NIP-17 mode)
- Drag-and-drop always enabled
- When files are attached in NIP-04 mode, auto-switches to NIP-17
  with snackbar: "Switched to NIP-17 — file attachments require
  encrypted messaging"
- NIP-17 toggle remains for manual control

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

desktopApp/src/jvmMain/kotlin/com/vitorpamplona/amethyst/desktop/ui/chats/ChatPane.kt

@@ -50,6 +50,8 @@ import androidx.compose.material3.Icon
 import androidx.compose.material3.IconButton
 import androidx.compose.material3.MaterialTheme
 import androidx.compose.material3.OutlinedTextField
+import androidx.compose.material3.SnackbarHost
+import androidx.compose.material3.SnackbarHostState
 import androidx.compose.material3.Surface
 import androidx.compose.material3.Text
 import androidx.compose.material3.TextButton
@@ -154,6 +156,20 @@ fun ChatPane(
     // File attachment state
     val attachedFiles = remember { mutableStateListOf<File>() }
     var isUploading by remember { mutableStateOf(false) }
+    val snackbarHostState = remember { SnackbarHostState() }
+
+    // Helper: attach files and auto-force NIP-17 if needed
+    fun attachFiles(files: List<File>) {
+        val mediaFiles = files.filter { it.extension.lowercase() in MEDIA_EXTENSIONS }
+        if (mediaFiles.isEmpty()) return
+        attachedFiles.addAll(mediaFiles)
+        if (!isNip17) {
+            messageState.toggleNip17()
+            scope.launch {
+                snackbarHostState.showSnackbar("Switched to NIP-17 — file attachments require encrypted messaging")
+            }
+        }
+    }
 
     // Drag-and-drop target for file attachments (NIP-17 only)
     var isDragOver by remember { mutableStateOf(false) }
@@ -168,7 +184,7 @@ fun ChatPane(
                     if (transferable.isDataFlavorSupported(DataFlavor.javaFileListFlavor)) {
                         @Suppress("UNCHECKED_CAST")
                         val files = transferable.getTransferData(DataFlavor.javaFileListFlavor) as List<File>
-                        attachedFiles.addAll(files.filter { it.extension.lowercase() in MEDIA_EXTENSIONS })
+                        attachFiles(files)
                         dropEvent.dropComplete(true)
                         return true
                     }
@@ -195,12 +211,13 @@ fun ChatPane(
         messageState.load(roomKey)
     }
 
+    Box(modifier = modifier.fillMaxSize()) {
         Column(
             modifier =
-            modifier
+                Modifier
                     .fillMaxSize()
                     .dragAndDropTarget(
-                    shouldStartDragAndDrop = { isNip17 },
+                        shouldStartDragAndDrop = { true },
                         target = dropTarget,
                     ).then(
                         if (isDragOver) {
@@ -316,14 +333,11 @@ fun ChatPane(
             HorizontalDivider()
 
             // File attachment row (only when NIP-17 and files attached)
-        if (isNip17 && attachedFiles.isNotEmpty()) {
+            if (attachedFiles.isNotEmpty()) {
                 MediaAttachmentRow(
                     attachedFiles = attachedFiles,
                     isUploading = isUploading,
-                onAttach = {
-                    val files = DesktopFilePicker.pickMediaFiles()
-                    attachedFiles.addAll(files)
-                },
+                    onAttach = { attachFiles(DesktopFilePicker.pickMediaFiles()) },
                     onPaste = {},
                     onRemove = { attachedFiles.remove(it) },
                 )
@@ -339,10 +353,7 @@ fun ChatPane(
                 hasAttachments = attachedFiles.isNotEmpty(),
                 onMessageChange = { messageState.updateMessage(messageText.copy(text = it)) },
                 onToggleNip17 = { messageState.toggleNip17() },
-            onAttach = {
-                val files = DesktopFilePicker.pickMediaFiles()
-                attachedFiles.addAll(files)
-            },
+                onAttach = { attachFiles(DesktopFilePicker.pickMediaFiles()) },
                 onSend = {
                     scope.launch {
                         if (attachedFiles.isNotEmpty()) {
@@ -373,7 +384,13 @@ fun ChatPane(
                     }
                 },
             )
-    }
+        } // end Column
+
+        SnackbarHost(
+            hostState = snackbarHostState,
+            modifier = Modifier.align(Alignment.BottomCenter).padding(bottom = 80.dp),
+        )
+    } // end Box
 }
 
 /**
@@ -674,8 +691,7 @@ private fun MessageInput(
             verticalAlignment = Alignment.CenterVertically,
             horizontalArrangement = Arrangement.spacedBy(8.dp),
         ) {
-            // Paperclip attach button (NIP-17 only)
-            if (isNip17) {
+            // Paperclip attach button — always visible, auto-switches to NIP-17 on send
             IconButton(
                 onClick = onAttach,
                 enabled = !isUploading,
@@ -692,7 +708,6 @@ private fun MessageInput(
                         },
                 )
             }
-            }
 
             OutlinedTextField(
                 value = messageText,