diff --git a/src/cli/App.tsx b/src/cli/App.tsx
index ebd571c..7966155 100644
--- a/src/cli/App.tsx
+++ b/src/cli/App.tsx
@@ -680,11 +680,17 @@ export default function App({
       initialInput: Array<MessageCreate | ApprovalCreate>,
     ): Promise<void> => {
       const currentInput = initialInput;
+      // Track lastRunId outside the while loop so it's available in catch block
+      let lastKnownRunId: string | null = null;
 
       try {
         setStreaming(true);
         abortControllerRef.current = new AbortController();
 
+        // 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);
+
         while (true) {
           // Stream one turn
           const stream = await sendMessageStream(agentId, currentInput);
@@ -696,6 +702,11 @@ export default function App({
               abortControllerRef.current?.signal,
             );
 
+          // Update lastKnownRunId for error handling in catch block
+          if (lastRunId) {
+            lastKnownRunId = lastRunId;
+          }
+
           // Track API duration
           sessionStatsRef.current.endTurn(apiDurationMs);
           sessionStatsRef.current.updateUsageFromBuffers(buffersRef.current);
@@ -902,8 +913,13 @@ export default function App({
           // Mark incomplete tool calls as finished to prevent stuck blinking UI
           markIncompleteToolsAsCancelled(buffersRef.current);
 
+          // Build run info suffix for debugging
+          const runInfoSuffix = lastRunId
+            ? `\n(run_id: ${lastRunId}, stop_reason: ${stopReason})`
+            : `\n(stop_reason: ${stopReason})`;
+
           // Fetch error details from the run if available
-          let errorDetails = `Unexpected stop reason: ${stopReason}`;
+          let errorDetails = `An error occurred during agent execution`;
           if (lastRunId) {
             try {
               const client = await getClient();
@@ -924,31 +940,43 @@ export default function App({
             } catch (_e) {
               // If we can't fetch error details, let user know
               appendError(
-                `${errorDetails}\n(Unable to fetch additional error details from server)`,
+                `${errorDetails}${runInfoSuffix}\n(Unable to fetch additional error details from server)`,
               );
               return;
             }
           }
 
-          appendError(errorDetails);
+          appendError(`${errorDetails}${runInfoSuffix}`);
 
           setStreaming(false);
           refreshDerived();
           return;
         }
       } catch (e) {
+        // Mark incomplete tool calls as cancelled to prevent stuck blinking UI
+        markIncompleteToolsAsCancelled(buffersRef.current);
+
+        // Build error message with run_id for debugging
+        const runIdSuffix = lastKnownRunId
+          ? `\n(run_id: ${lastKnownRunId}, stop_reason: error)`
+          : "";
+
         // Handle APIError from streaming (event: error)
         if (e instanceof APIError && e.error?.error) {
           const { type, message, detail } = e.error.error;
           const errorType = type ? `[${type}] ` : "";
           const errorMessage = message || "An error occurred";
           const errorDetail = detail ? `:\n${detail}` : "";
-          appendError(`${errorType}${errorMessage}${errorDetail}`);
+          appendError(
+            `${errorType}${errorMessage}${errorDetail}${runIdSuffix}`,
+          );
         } else {
           // Fallback for non-API errors
-          appendError(e instanceof Error ? e.message : String(e));
+          const errorMessage = e instanceof Error ? e.message : String(e);
+          appendError(`${errorMessage}${runIdSuffix}`);
         }
         setStreaming(false);
+        refreshDerived();
       } finally {
         abortControllerRef.current = null;
       }
diff --git a/src/headless.ts b/src/headless.ts
index fd29071..8292ec8 100644
--- a/src/headless.ts
+++ b/src/headless.ts
@@ -13,7 +13,11 @@ import { createAgent } from "./agent/create";
 import { sendMessageStream } from "./agent/message";
 import { getModelUpdateArgs } from "./agent/model";
 import { SessionStats } from "./agent/stats";
-import { createBuffers, toLines } from "./cli/helpers/accumulator";
+import {
+  createBuffers,
+  markIncompleteToolsAsCancelled,
+  toLines,
+} from "./cli/helpers/accumulator";
 import { safeJsonParseOr } from "./cli/helpers/safeJsonParse";
 import { drainStreamWithResume } from "./cli/helpers/stream";
 import { settingsManager } from "./settings-manager";
@@ -424,6 +428,9 @@ export async function handleHeadlessCommand(
     },
   ];
 
+  // Track lastRunId outside the while loop so it's available in catch block
+  let lastKnownRunId: string | null = null;
+
   try {
     while (true) {
       const stream = await sendMessageStream(agent.id, currentInput);
@@ -643,6 +650,7 @@ export async function handleHeadlessCommand(
         apiDurationMs = performance.now() - startTime;
         // Use the last run_id we saw (if any)
         lastRunId = runIds.size > 0 ? Array.from(runIds).pop() || null : null;
+        if (lastRunId) lastKnownRunId = lastRunId;
 
         // Mark final line as finished
         const { markCurrentLineAsFinished } = await import(
@@ -660,6 +668,7 @@ export async function handleHeadlessCommand(
         approvals = result.approvals || [];
         apiDurationMs = result.apiDurationMs;
         lastRunId = result.lastRunId || null;
+        if (lastRunId) lastKnownRunId = lastRunId;
       }
 
       // Track API duration for this stream
@@ -772,6 +781,9 @@ export async function handleHeadlessCommand(
       }
 
       // Unexpected stop reason (error, llm_api_error, etc.)
+      // Mark incomplete tool calls as cancelled to prevent stuck state
+      markIncompleteToolsAsCancelled(buffers);
+
       // Extract error details from buffers if available
       const errorLines = toLines(buffers).filter(
         (line) => line.kind === "error",
@@ -813,24 +825,39 @@ export async function handleHeadlessCommand(
             type: "error",
             message: errorMessage,
             stop_reason: stopReason,
+            run_id: lastRunId,
           }),
         );
       } else {
-        console.error(errorMessage);
+        // Include run_id and stop_reason for debugging
+        const runInfoSuffix = lastRunId
+          ? ` (run_id: ${lastRunId}, stop_reason: ${stopReason})`
+          : ` (stop_reason: ${stopReason})`;
+        console.error(`${errorMessage}${runInfoSuffix}`);
       }
       process.exit(1);
     }
   } catch (error) {
+    // Mark incomplete tool calls as cancelled
+    markIncompleteToolsAsCancelled(buffers);
+
+    // Build run info suffix for debugging
+    const runInfoSuffix = lastKnownRunId
+      ? ` (run_id: ${lastKnownRunId}, stop_reason: error)`
+      : "";
+
     // Handle APIError from streaming (event: error)
     if (error instanceof APIError && error.error?.error) {
       const { type, message, detail } = error.error.error;
       const errorType = type ? `[${type}] ` : "";
       const errorMessage = message || "An error occurred";
       const errorDetail = detail ? `: ${detail}` : "";
-      console.error(`Error: ${errorType}${errorMessage}${errorDetail}`);
+      console.error(
+        `Error: ${errorType}${errorMessage}${errorDetail}${runInfoSuffix}`,
+      );
     } else {
       // Fallback for non-API errors
-      console.error(`Error: ${error}`);
+      console.error(`Error: ${error}${runInfoSuffix}`);
     }
     process.exit(1);
   }