fix: handle mid-stream errors properly using sdk typing (#54)

src/cli/App.tsx

@@ -1,5 +1,6 @@
 // src/cli/App.tsx
 
+import { APIError } from "@letta-ai/letta-client/core/error";
 import type {
   AgentState,
   MessageCreate,
@@ -535,7 +536,17 @@ export default function App({
           return;
         }
       } catch (e) {
-        appendError(String(e));
+        // Handle APIError from streaming (event: error)
+        if (e instanceof APIError && e.error?.error) {
+          const { type, message, detail } = e.error.error;
+          const errorType = type ? `[${type}] ` : "";
+          const errorMessage = message || "An error occurred";
+          const errorDetail = detail ? `:\n${detail}` : "";
+          appendError(`${errorType}${errorMessage}${errorDetail}`);
+        } else {
+          // Fallback for non-API errors
+          appendError(e instanceof Error ? e.message : String(e));
+        }
         setStreaming(false);
       } finally {
         abortControllerRef.current = null;
@@ -560,13 +571,14 @@ export default function App({
       const client = await getClient();
 
       // Send cancel request to backend
-      await client.agents.messages.cancel(agentId);
+      const cancelResult = await client.agents.messages.cancel(agentId);
+      // console.error("cancelResult", JSON.stringify(cancelResult, null, 2));
 
       // WORKAROUND: Also abort the stream immediately since backend cancellation is buggy
       // TODO: Once backend is fixed, comment out the immediate abort below and uncomment the timeout version
-      if (abortControllerRef.current) {
+      // if (abortControllerRef.current) {
-        abortControllerRef.current.abort();
+      //   abortControllerRef.current.abort();
-      }
+      // }
 
       // FUTURE: Use this timeout-based abort once backend properly sends "cancelled" stop reason
       // This gives the backend 5 seconds to gracefully close the stream before forcing abort

src/cli/helpers/accumulator.ts

@@ -197,26 +197,8 @@ function extractTextPart(v: unknown): string {
 export function onChunk(b: Buffers, chunk: LettaStreamingResponse) {
   // TODO remove once SDK v1 has proper typing for in-stream errors
   // Check for streaming error objects (not typed in SDK but emitted by backend)
-  // These are emitted when LLM errors occur during streaming (rate limits, timeouts, etc.)
+  // Note: Error handling moved to catch blocks in App.tsx and headless.ts
-  const chunkWithError = chunk as typeof chunk & {
+  // The SDK now throws APIError when it sees event: error, so chunks never have error property
-    error?: { message?: string; detail?: string };
-  };
-  if (chunkWithError.error && !chunk.message_type) {
-    const errorId = `err-${Date.now().toString(36)}-${Math.random().toString(36).slice(2, 8)}`;
-    const errorMsg = chunkWithError.error.message || "An error occurred";
-    const errorDetail = chunkWithError.error.detail || "";
-    const fullErrorText = errorDetail
-      ? `${errorMsg}: ${errorDetail}`
-      : errorMsg;
-
-    b.byId.set(errorId, {
-      kind: "error",
-      id: errorId,
-      text: `⚠ ${fullErrorText}`,
-    });
-    b.order.push(errorId);
-    return;
-  }
 
   switch (chunk.message_type) {
     case "reasoning_message": {

src/cli/helpers/stream.ts

@@ -117,6 +117,11 @@ export async function drainStream(
     stopReason = "error";
   }
 
+  // Mark incomplete tool calls as cancelled if stream was cancelled
+  if (stopReason === "cancelled") {
+    markIncompleteToolsAsCancelled(buffers);
+  }
+
   // Mark the final line as finished now that stream has ended
   markCurrentLineAsFinished(buffers);
   queueMicrotask(refresh);

src/headless.ts

@@ -1,4 +1,5 @@
 import { parseArgs } from "node:util";
+import { APIError } from "@letta-ai/letta-client/core/error";
 import type {
   AgentState,
   MessageCreate,
@@ -575,7 +576,17 @@ export async function handleHeadlessCommand(argv: string[], model?: string) {
       process.exit(1);
     }
   } catch (error) {
-    console.error(`Error: ${error}`);
+    // Handle APIError from streaming (event: error)
+    if (error instanceof APIError && error.error?.error) {
+      const { type, message, detail } = error.error.error;
+      const errorType = type ? `[${type}] ` : "";
+      const errorMessage = message || "An error occurred";
+      const errorDetail = detail ? `: ${detail}` : "";
+      console.error(`Error: ${errorType}${errorMessage}${errorDetail}`);
+    } else {
+      // Fallback for non-API errors
+      console.error(`Error: ${error}`);
+    }
     process.exit(1);
   }