fix: SFTP sidebar empty on load — list sent before WebSocket open

The list('/') call fired immediately after connect(), but the
WebSocket was still in CONNECTING state so send() silently dropped
the message. Now buffers the initial list request and sends it
in the onopen callback.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

frontend/composables/useSftp.ts

@@ -9,10 +9,19 @@ export function useSftp(sessionId: Ref<string | null>) {
   const fileContent = ref<{ path: string; content: string } | null>(null)
   const transfers = ref<any[]>([])
 
+  let pendingList: string | null = null
+
   function connect() {
     const wsUrl = `${location.protocol === 'https:' ? 'wss' : 'ws'}://${location.host}/api/ws/sftp?token=${auth.token}`
     ws = new WebSocket(wsUrl)
 
+    ws.onopen = () => {
+      if (pendingList !== null) {
+        send({ type: 'list', path: pendingList })
+        pendingList = null
+      }
+    }
+
     ws.onmessage = (event) => {
       const msg = JSON.parse(event.data)
       switch (msg.type) {
@@ -48,7 +57,13 @@ export function useSftp(sessionId: Ref<string | null>) {
     }
   }
 
-  function list(path: string) { send({ type: 'list', path }) }
+  function list(path: string) {
+    if (ws && ws.readyState === WebSocket.OPEN) {
+      send({ type: 'list', path })
+    } else {
+      pendingList = path
+    }
+  }
   function readFile(path: string) { send({ type: 'read', path }) }
   function writeFile(path: string, data: string) { send({ type: 'write', path, data }) }
   function mkdir(path: string) { send({ type: 'mkdir', path }) }