feat: add API key caching via settings.json (#16)

Co-authored-by: Letta <noreply@letta.com>

src/agent/client.ts

@@ -1,13 +1,41 @@
 import { LettaClient } from "@letta-ai/letta-client";
+import { loadSettings, updateSettings } from "../settings";
 
-export function getClient() {
-  const token = process.env.LETTA_API_KEY;
+export async function getClient() {
+  const settings = await loadSettings();
+
+  const token = process.env.LETTA_API_KEY || settings.env?.LETTA_API_KEY;
   if (!token) {
     console.error("Missing LETTA_API_KEY");
+    console.error(
+      "Set it via environment variable or add it to ~/.letta/settings.json:",
+    );
+    console.error('  { "env": { "LETTA_API_KEY": "sk-let-..." } }');
     process.exit(1);
   }
 
-  const baseUrl = process.env.LETTA_BASE_URL || "https://api.letta.com";
+  const baseUrl =
+    process.env.LETTA_BASE_URL ||
+    settings.env?.LETTA_BASE_URL ||
+    "https://api.letta.com";
+
+  // Auto-cache: if env vars are set but not in settings, write them to settings
+  let needsUpdate = false;
+  const updatedEnv = { ...settings.env };
+
+  if (process.env.LETTA_API_KEY && !settings.env?.LETTA_API_KEY) {
+    updatedEnv.LETTA_API_KEY = process.env.LETTA_API_KEY;
+    needsUpdate = true;
+  }
+
+  if (process.env.LETTA_BASE_URL && !settings.env?.LETTA_BASE_URL) {
+    updatedEnv.LETTA_BASE_URL = process.env.LETTA_BASE_URL;
+    needsUpdate = true;
+  }
+
+  if (needsUpdate) {
+    await updateSettings({ env: updatedEnv });
+  }
 
   return new LettaClient({ token, baseUrl });
 }

src/agent/create.ts

@@ -17,7 +17,7 @@ export async function createAgent(
   name = "letta-cli-agent",
   model = "anthropic/claude-sonnet-4-5-20250929",
 ) {
-  const client = getClient();
+  const client = await getClient();
 
   // Get loaded tool names (tools are already registered with Letta)
   const toolNames = [

src/agent/message.ts

@@ -14,7 +14,7 @@ export async function sendMessageStream(
     // add more later: includePings, request timeouts, etc.
   } = { streamTokens: true, background: true },
 ): Promise<AsyncIterable<Letta.LettaStreamingResponse>> {
-  const client = getClient();
+  const client = await getClient();
   return client.agents.messages.createStream(agentId, {
     messages: messages,
     streamTokens: opts.streamTokens ?? true,

src/agent/modify.ts

@@ -20,7 +20,7 @@ export async function updateAgentLLMConfig(
   modelHandle: string,
   updateArgs?: Record<string, unknown>,
 ): Promise<Letta.LlmConfig> {
-  const client = getClient();
+  const client = await getClient();
 
   // Step 1: Update model (top-level field)
   await client.agents.modify(agentId, { model: modelHandle });