fix: Fetch error shown as string (not [object Object]); extract API error from response body; guard fetch availability

src/main.ts

@@ -504,14 +504,25 @@ export default function () {
 
   // UI asks to list models for a provider. Network must run here (main thread) —
   // the plugin UI iframe is CSP-sandboxed and cannot fetch external URLs.
-  on('FETCH_MODELS', async function (payload: { baseUrl: string, apiKey: string }) {
+  on('FETCH_MODELS', async function (payload: any) {
     try {
+      if (typeof fetch !== 'function') {
+        emit('MODELS_RESULT', { ok: false, error: 'fetch is not available in the plugin main thread', models: [] })
+        return
+      }
       const base = payload.baseUrl.replace(/\/+$/, '')
       const res = await fetch(base + '/models', {
         headers: { Authorization: 'Bearer ' + payload.apiKey }
       })
       if (!res.ok) {
-        emit('MODELS_RESULT', { ok: false, error: 'HTTP ' + res.status, models: [] })
+        let msg = 'HTTP ' + res.status
+        try {
+          const body = JSON.parse(await res.text())
+          if (body != null && body.error != null) {
+            msg = typeof body.error === 'string' ? body.error : (body.error.message || JSON.stringify(body.error))
+          }
+        } catch (e) { /* keep HTTP status message */ }
+        emit('MODELS_RESULT', { ok: false, error: msg, models: [] })
         return
       }
       const json: any = await res.json()
@@ -523,7 +534,8 @@ export default function () {
       }
       emit('MODELS_RESULT', { ok: true, models })
     } catch (e) {
-      emit('MODELS_RESULT', { ok: false, error: String(e), models: [] })
+      const msg = e instanceof Error ? e.message : (e != null ? String(e) : 'Unknown error')
+      emit('MODELS_RESULT', { ok: false, error: msg, models: [] })
     }
   })