fix(cursor): surface agent errors with warning styling in web UI (#871)

* test: reproduce issue #864

Assert Cursor error paths emit agent error payloads and web UI renders
them as warning-styled events instead of neutral session messages.

Co-authored-by: Cursor <cursoragent@cursor.com>

* fix(cursor): surface agent errors with warning styling in web UI (closes #864)

Route Cursor stderr, init, prompt, and legacy exit failures through
sendAgentMessage({ type: 'error' }) and teach the web chat layer to
render error events with a warning icon instead of neutral info text.

Co-authored-by: Cursor <cursoragent@cursor.com>

---------

Co-authored-by: Cursor <cursoragent@cursor.com>

web/src/chat/normalize.test.ts

@@ -178,6 +178,27 @@ describe('normalizeDecryptedMessage', () => {
         })
     })
 
+    it('normalizes agent error payloads as error events', () => {
+        const normalized = normalizeDecryptedMessage(makeMessage({
+            role: 'agent',
+            content: {
+                type: 'codex',
+                data: {
+                    type: 'error',
+                    message: 'Cursor Agent failed: authentication required'
+                }
+            }
+        }))
+
+        expect(normalized).toMatchObject({
+            role: 'event',
+            content: {
+                type: 'error',
+                message: 'Cursor Agent failed: authentication required'
+            }
+        })
+    })
+
     it('treats non-sidechain string user output as sidechain', () => {
         const message = makeMessage({
             role: 'agent',

web/src/chat/normalizeAgent.ts

@@ -577,6 +577,21 @@ export function normalizeAgentRecord(
             }
         }
 
+        if (data.type === 'error' && typeof data.message === 'string') {
+            return {
+                id: messageId,
+                localId,
+                createdAt,
+                role: 'event',
+                content: {
+                    type: 'error',
+                    message: data.message
+                },
+                isSidechain: false,
+                meta
+            }
+        }
+
         if (data.type === 'message' && typeof data.message === 'string') {
             const review = parseCodexReviewMessage(data.message)
             if (review) {

web/src/chat/presentation.test.ts

@@ -1,6 +1,18 @@
 import { describe, expect, it } from 'vitest'
 import { getEventPresentation, formatMessageTimestamp, formatResetTime } from './presentation'
 
+describe('getEventPresentation — agent errors', () => {
+    it('formats error events with warning icon and message text', () => {
+        const result = getEventPresentation({
+            type: 'error',
+            message: 'Cursor Agent failed: authentication required'
+        })
+
+        expect(result.icon).toBe('⚠️')
+        expect(result.text).toBe('Cursor Agent failed: authentication required')
+    })
+})
+
 describe('getEventPresentation — limit-warning', () => {
     it('formats five_hour warning', () => {
         const result = getEventPresentation({

web/src/chat/presentation.ts

@@ -182,6 +182,9 @@ export function getEventPresentation(event: AgentEvent): EventPresentation {
         const suffix = typeLabel ? ` (${typeLabel})` : ''
         return { icon: '⏳', text: endsAt ? `Usage limit reached${suffix} until ${formatUnixTimestamp(endsAt)}` : `Usage limit reached${suffix}` }
     }
+    if (event.type === 'error') {
+        return { icon: '⚠️', text: typeof event.message === 'string' ? event.message : 'Error' }
+    }
     if (event.type === 'message') {
         return { icon: null, text: typeof event.message === 'string' ? event.message : 'Message' }
     }

web/src/chat/reducerEvents.ts

@@ -79,6 +79,18 @@ export function dedupeAgentEvents(blocks: ChatBlock[]): ChatBlock[] {
             continue
         }
 
+        if (event.type === 'error' && typeof event.message === 'string') {
+            const message = event.message.trim()
+            const key = `error:${message}`
+            if (key === prevEventKey) {
+                continue
+            }
+            result.push(block)
+            prevEventKey = key
+            prevTitleChangedTo = null
+            continue
+        }
+
         let key: string
         try {
             key = `event:${JSON.stringify(event)}`

web/src/chat/reducerTimeline.ts

@@ -180,6 +180,15 @@ function normalizeTraceMessage(
         meta: source.meta
     }
 
+    if (data.type === 'error' && typeof data.message === 'string') {
+        return [{
+            ...base,
+            id: traceId,
+            role: 'event',
+            content: { type: 'error', message: data.message }
+        } as TracedMessage]
+    }
+
     if (data.type === 'message' && typeof data.message === 'string') {
         return [{
             ...base,

web/src/chat/types.ts

@@ -16,6 +16,7 @@ export type UsageData = {
 export type AgentEvent =
     | { type: 'switch'; mode: 'local' | 'remote' }
     | { type: 'message'; message: string }
+    | { type: 'error'; message: string }
     | { type: 'title-changed'; title: string }
     | { type: 'limit-reached'; endsAt: number; limitType: string }
     | { type: 'limit-warning'; /** 0–1 ratio (e.g. 0.9 = 90%), integer-precision via CLI pipe format */ utilization: number; endsAt: number; limitType: string }