fix: prevent stale stream updates after interrupt (#318)

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

src/cli/App.tsx

@@ -654,7 +654,11 @@ export default function App({
       buffersRef.current.pendingRefresh = true;
       setTimeout(() => {
         buffersRef.current.pendingRefresh = false;
-        refreshDerived();
+        // Skip refresh if stream was interrupted - prevents stale updates appearing
+        // after user cancels. Normal stream completion still renders (interrupted=false).
+        if (!buffersRef.current.interrupted) {
+          refreshDerived();
+        }
       }, 16); // ~60fps
     }
   }, [refreshDerived]);
@@ -828,6 +832,8 @@ export default function App({
         // Clear any stale pending tool calls from previous turns
         // If we're sending a new message, old pending state is no longer relevant
         markIncompleteToolsAsCancelled(buffersRef.current);
+        // Reset interrupted flag since we're starting a fresh stream
+        buffersRef.current.interrupted = false;
 
         // Clear completed subagents from the UI when starting a new turn
         clearCompletedSubagents();
@@ -3013,6 +3019,8 @@ ${recentCommits}
 
       // Reset token counter for this turn (only count the agent's response)
       buffersRef.current.tokenCount = 0;
+      // Clear interrupted flag from previous turn
+      buffersRef.current.interrupted = false;
       // Rotate to a new thinking message for this turn
       setThinkingMessage(getRandomThinkingVerb());
       // Show streaming state immediately for responsiveness
@@ -3412,6 +3420,8 @@ ${recentCommits}
 
         // Show "thinking" state and lock input while executing approved tools client-side
         setStreaming(true);
+        // Ensure interrupted flag is cleared for this execution
+        buffersRef.current.interrupted = false;
 
         const approvalAbortController = new AbortController();
         toolAbortControllerRef.current = approvalAbortController;

src/cli/helpers/accumulator.ts

@@ -62,6 +62,7 @@ export type Buffers = {
   toolCallIdToLineId: Map<string, string>;
   lastOtid: string | null; // Track the last otid to detect transitions
   pendingRefresh?: boolean; // Track throttled refresh state
+  interrupted?: boolean; // Track if stream was interrupted by user (skip stale refreshes)
   usage: {
     promptTokens: number;
     completionTokens: number;
@@ -162,6 +163,9 @@ export function markCurrentLineAsFinished(b: Buffers) {
  * This prevents blinking tool calls from staying in progress state.
  */
 export function markIncompleteToolsAsCancelled(b: Buffers) {
+  // Mark buffer as interrupted to skip stale throttled refreshes
+  b.interrupted = true;
+
   for (const [id, line] of b.byId.entries()) {
     if (line.kind === "tool_call" && line.phase !== "finished") {
       const updatedLine = {

src/cli/helpers/stream.ts

@@ -141,10 +141,7 @@ export async function drainStream(
       }
     }
 
-    onChunk(buffers, chunk);
-    queueMicrotask(refresh);
-
-    // Check abort signal again after processing chunk (for eager cancellation)
+    // Check abort signal before processing - don't add data after interrupt
     if (abortSignal?.aborted) {
       stopReason = "cancelled";
       markIncompleteToolsAsCancelled(buffers);
@@ -152,6 +149,9 @@ export async function drainStream(
       break;
     }
 
+    onChunk(buffers, chunk);
+    queueMicrotask(refresh);
+
     if (chunk.message_type === "stop_reason") {
       stopReason = chunk.stop_reason;
       // Continue reading stream to get usage_statistics that may come after