fix: always populate user-agent (#708)

src/agent/http-headers.ts

@@ -0,0 +1,24 @@
+import packageJson from "../../package.json";
+
+/**
+ * Get standard headers for manual HTTP calls to Letta API.
+ * Use this for any direct fetch() calls (not SDK calls).
+ */
+export function getLettaCodeHeaders(apiKey?: string): Record<string, string> {
+  return {
+    "Content-Type": "application/json",
+    "User-Agent": `letta-code/${packageJson.version}`,
+    "X-Letta-Source": "letta-code",
+    ...(apiKey ? { Authorization: `Bearer ${apiKey}` } : {}),
+  };
+}
+
+/**
+ * Get headers for MCP OAuth connections (includes Accept header for SSE).
+ */
+export function getMcpOAuthHeaders(apiKey: string): Record<string, string> {
+  return {
+    ...getLettaCodeHeaders(apiKey),
+    Accept: "text/event-stream",
+  };
+}