feat(agentctl): exportGuildSyncDiagnostics headless helper

Expose platform sync diagnostics export for mesh/sync validation scenarios.

Co-authored-by: Cursor <[email protected]>

headless.js

@@ -1012,6 +1012,11 @@ class HeadlessSession {
     return out
   }
 
+  exportGuildSyncDiagnostics (guildId) {
+    if (!this.platform) throw new Error('headless not started')
+    return this.platform.exportGuildSyncDiagnostics(guildId)
+  }
+
   async revokeGuildInvite (code) {
     if (!this.platform) throw new Error('headless not started')
     const result = await this.platform.revokeInvite(code)