diff --git a/src/renderer/src/lib/worktree-status.ts b/src/renderer/src/lib/worktree-status.ts
index e12d197dda9..6f39d8c1e0b 100644
--- a/src/renderer/src/lib/worktree-status.ts
+++ b/src/renderer/src/lib/worktree-status.ts
@@ -2,7 +2,7 @@ import { resolveAgentTypeFromTerminalTitle } from '@/components/sidebar/worktree
 import { classifyTitleActivity } from '@/lib/pane-agent-evidence'
 import { tabHasLivePty } from '@/lib/tab-has-live-pty'
 import { resolveRuntimePaneTitleLeafIdFromRoot } from '@/lib/runtime-pane-title-leaf-id'
-import { containsBrailleSpinner } from '../../../shared/agent-title-core'
+import { containsAgentSpinnerGlyph } from '../../../shared/agent-title-core'
 import type {
   TerminalLayoutSnapshot,
   TerminalPaneLayoutNode,
@@ -106,7 +106,7 @@ function titleStatusIsAgentAttributable(title: string, launchAgent?: TuiAgent |
   // Why: a spinner proves activity but not identity (Claude's thinking title has no provider
   // token, #9040); the tab's launch identity supplies it, mirroring the row builder's spinner
   // fallback (#9647) so the dot and the sidebar row agree.
-  return containsBrailleSpinner(title) && Boolean(launchAgent)
+  return containsAgentSpinnerGlyph(title) && Boolean(launchAgent)
 }
 
 export function getWorktreeStatusLabel(status: WorktreeStatus): string {
diff --git a/src/shared/agent-decorative-title-signature.ts b/src/shared/agent-decorative-title-signature.ts
index 29f1a65e6a2..317a744d098 100644
--- a/src/shared/agent-decorative-title-signature.ts
+++ b/src/shared/agent-decorative-title-signature.ts
@@ -27,7 +27,10 @@ function normalizeDecorativeAgentTitleText(title: string): string {
   let pendingWhitespace = false
   for (let index = 0; index < title.length; index += 1) {
     const code = title.charCodeAt(index)
-    if (normalized.length === 0 && (isDecorativeTitleWhitespace(code) || isBrailleSpinner(code))) {
+    if (
+      normalized.length === 0 &&
+      (isDecorativeTitleWhitespace(code) || isSpinnerFrameGlyph(code))
+    ) {
       continue
     }
     if (isDecorativeTitleWhitespace(code)) {
@@ -43,8 +46,9 @@ function normalizeDecorativeAgentTitleText(title: string): string {
   return normalized
 }
 
-function isBrailleSpinner(code: number): boolean {
-  return code >= 0x2800 && code <= 0x28ff
+// Why: braille (most agents) plus quarter circles (Claude Code 2.1.228+, #13889).
+function isSpinnerFrameGlyph(code: number): boolean {
+  return (code >= 0x2800 && code <= 0x28ff) || (code >= 0x25d0 && code <= 0x25d3)
 }
 
 function isDecorativeTitleWhitespace(code: number): boolean {
diff --git a/src/shared/agent-title-core.ts b/src/shared/agent-title-core.ts
index 83dcc12bf92..c96121b432c 100644
--- a/src/shared/agent-title-core.ts
+++ b/src/shared/agent-title-core.ts
@@ -47,6 +47,11 @@ export const CURSOR_NATIVE_TITLE_LOWER = 'cursor agent'
 // eslint-disable-next-line no-control-regex -- intentional unicode range
 export const BRAILLE_SPINNER_RE = /[\u2800-\u28ff]/g
 
+// Why: Claude Code 2.1.228 swapped its busy title spinner from braille to
+// quarter circles (#13889), which read as "no agent" and looked like an exit.
+// Reserve the whole quarter-circle block so a later frame addition cannot regress this.
+export const QUARTER_CIRCLE_SPINNER_RE = /[\u25d0-\u25d3]/g
+
 export function isGeminiTerminalTitle(title: string): boolean {
   // Why: Gemini OSC glyphs are stronger evidence than any cwd/session text.
   if (
@@ -83,6 +88,25 @@ export function containsBrailleSpinner(title: string): boolean {
   return false
 }
 
+export function containsQuarterCircleSpinner(title: string): boolean {
+  for (const char of title) {
+    const codePoint = char.codePointAt(0)
+    if (codePoint !== undefined && codePoint >= 0x25d0 && codePoint <= 0x25d3) {
+      return true
+    }
+  }
+  return false
+}
+
+/**
+ * Any spinner frame glyph an agent animates its OSC title with. Use this for
+ * generic "something is running" checks; agent-specific frame shapes (Grok,
+ * Pi, synthetic Cursor) stay pinned to their own glyph set.
+ */
+export function containsAgentSpinnerGlyph(title: string): boolean {
+  return containsBrailleSpinner(title) || containsQuarterCircleSpinner(title)
+}
+
 export function containsLegacyAgentName(title: string): boolean {
   return titleHasAnyLegacyAgentName(title)
 }
diff --git a/src/shared/agent-title-decoration.ts b/src/shared/agent-title-decoration.ts
index bc05badf8aa..47a6db679e7 100644
--- a/src/shared/agent-title-decoration.ts
+++ b/src/shared/agent-title-decoration.ts
@@ -1,11 +1,11 @@
 // Leading status decorations that coding agents prepend to their OSC title —
-// Claude's '✳', Gemini's glyphs (✦ ⏲ ◇ ✋), braille spinners, and Claude's
-// '. '/'* ' working/idle prefixes. Once the tab bar shows the provider icon,
-// this leading glyph reads as a redundant second icon, so strip it from the
-// displayed title. Scoped to titles we already know belong to an agent.
+// Claude's '✳', Gemini's glyphs (✦ ⏲ ◇ ✋), braille and quarter-circle spinners,
+// and Claude's '. '/'* ' working/idle prefixes. Once the tab bar shows the
+// provider icon, this leading glyph reads as a redundant second icon, so strip
+// it from the displayed title. Scoped to titles we already know belong to an agent.
 const LEADING_AGENT_TITLE_DECORATION_RE =
   // eslint-disable-next-line no-control-regex -- intentional unicode status-glyph ranges
-  /^(?:[✳✦⏲◇✋⠀-⣿]+|[.*]\s)\s*/
+  /^(?:[✳✦⏲◇✋⠀-⣿◐-◓]+|[.*]\s)\s*/
 
 export function stripLeadingAgentTitleDecorationOrEmpty(title: string): string {
   return title.replace(LEADING_AGENT_TITLE_DECORATION_RE, '').trimStart()
diff --git a/src/shared/agent-title-identity.ts b/src/shared/agent-title-identity.ts
index af86de1667d..cdfc6946777 100644
--- a/src/shared/agent-title-identity.ts
+++ b/src/shared/agent-title-identity.ts
@@ -3,7 +3,7 @@ import {
   CLAUDE_IDLE,
   DROID_AGENT_NAME_RE,
   HERMES_AGENT_NAME_RE,
-  containsBrailleSpinner,
+  containsAgentSpinnerGlyph,
   isClaudeManagementTitle,
   isCursorAgentTitle,
   isGeminiTerminalTitle,
@@ -31,7 +31,7 @@ export function isClaudeAgent(title: string): boolean {
   if (title.startsWith('. ') || title.startsWith('* ')) {
     return true
   }
-  if (containsBrailleSpinner(title)) {
+  if (containsAgentSpinnerGlyph(title)) {
     // Why: named non-Claude agents carry braille spinners too. Gate Cursor by its
     // identity title, not the token, so a Claude title mentioning a cursor stays Claude.
     return !isCursorAgentTitle(title) && !lower.includes('openclaude')
diff --git a/src/shared/agent-title-status.ts b/src/shared/agent-title-status.ts
index 09ffc07a677..551acf87328 100644
--- a/src/shared/agent-title-status.ts
+++ b/src/shared/agent-title-status.ts
@@ -9,12 +9,13 @@ import {
   GEMINI_SILENT_WORKING,
   GEMINI_WORKING,
   HERMES_AGENT_NAME_RE,
+  QUARTER_CIRCLE_SPINNER_RE,
   STRONG_IDLE_KEYWORDS_RE,
   STRONG_WORKING_KEYWORDS_RE,
   STRONG_WORKING_KEYWORDS_RE_GLOBAL,
   containsAgentName,
+  containsAgentSpinnerGlyph,
   containsAny,
-  containsBrailleSpinner,
   containsLegacyAgentName,
   isClaudeManagementTitle,
   isGeminiTerminalTitle,
@@ -34,6 +35,7 @@ export function clearWorkingIndicators(title: string): string {
   cleaned = cleaned.replace(GEMINI_WORKING, '')
   cleaned = cleaned.replace(GEMINI_SILENT_WORKING, '')
   cleaned = cleaned.replace(BRAILLE_SPINNER_RE, '')
+  cleaned = cleaned.replace(QUARTER_CIRCLE_SPINNER_RE, '')
   if (cleaned.startsWith('. ')) {
     cleaned = cleaned.slice(2)
   }
@@ -181,7 +183,7 @@ export function detectAgentStatusFromTitle(title: string): AgentStatus | null {
   if (isPiTerminalTitle(title)) {
     return 'idle'
   }
-  if (containsBrailleSpinner(title)) {
+  if (containsAgentSpinnerGlyph(title)) {
     return 'working'
   }
 
diff --git a/src/shared/repro-13889-claude-quarter-circle-busy-title.test.ts b/src/shared/repro-13889-claude-quarter-circle-busy-title.test.ts
new file mode 100644
index 00000000000..6156489a567
--- /dev/null
+++ b/src/shared/repro-13889-claude-quarter-circle-busy-title.test.ts
@@ -0,0 +1,99 @@
+import { describe, expect, it } from 'vitest'
+
+import {
+  clearWorkingIndicators,
+  createAgentStatusTracker,
+  detectAgentStatusFromTitle,
+  getAgentLabel,
+  isClaudeAgent
+} from './agent-detection'
+import { isDecorativeAgentTitleFrameChange } from './agent-decorative-title-signature'
+import { stripLeadingAgentTitleDecoration } from './agent-title-decoration'
+import { resolveExplicitTerminalTitleAgentType } from './terminal-title-agent-type'
+
+// Titles captured from real `claude` binaries running the same one-line prompt.
+// 2.1.228 swapped the busy spinner from braille to quarter circles, which read as
+// "no agent" and made the tracker report a confirmed exit mid-turn (#13889).
+const BUSY_2_1_227 = ['⠂ Claude Code', '⠐ Claude Code', '⠂ Say hi in one word'] as const
+const BUSY_2_1_228 = ['◐ Claude Code', '◑ Claude Code', '◑ Say hi in one word'] as const
+
+const CAPTURED_2_1_228_TURN = [
+  '✳ Claude Code',
+  '◐ Claude Code',
+  '◑ Claude Code',
+  '◑ Say hi in one word',
+  '◐ Say hi in one word',
+  '✳ Say hi in one word'
+] as const
+
+function trackTurn(titles: readonly string[]): string[] {
+  const events: string[] = []
+  const tracker = createAgentStatusTracker(
+    () => events.push('idle'),
+    () => events.push('working'),
+    () => events.push('exited')
+  )
+  for (const title of titles) {
+    tracker.handleTitle(title)
+  }
+  return events
+}
+
+describe('Claude Code quarter-circle busy titles (#13889)', () => {
+  it('reports working for every quarter-circle spinner frame', () => {
+    for (const title of ['◐ Claude Code', '◑ Claude Code', '◒ Claude Code', '◓ Claude Code']) {
+      expect(detectAgentStatusFromTitle(title)).toBe('working')
+    }
+  })
+
+  it('reports working when the busy title carries task text instead of the agent name', () => {
+    // Why: the summary-bearing frame has no "claude" token, so it previously fell
+    // through to null — the value the tracker reads as an exit.
+    expect(detectAgentStatusFromTitle('◐ Say hi in one word')).toBe('working')
+  })
+
+  it('keeps Claude identity while busy', () => {
+    for (const title of BUSY_2_1_228) {
+      expect(isClaudeAgent(title)).toBe(true)
+      expect(getAgentLabel(title)).toBe('Claude Code')
+    }
+  })
+
+  it('matches 2.1.227 status and identity frame for frame', () => {
+    BUSY_2_1_228.forEach((title, index) => {
+      const braille = BUSY_2_1_227[index]
+      expect(detectAgentStatusFromTitle(title)).toBe(detectAgentStatusFromTitle(braille))
+      expect(getAgentLabel(title)).toBe(getAgentLabel(braille))
+      expect(resolveExplicitTerminalTitleAgentType(title)).toBe(
+        resolveExplicitTerminalTitleAgentType(braille)
+      )
+    })
+  })
+
+  it('never confirms an agent exit across a real 2.1.228 turn', () => {
+    const events = trackTurn(CAPTURED_2_1_228_TURN)
+    expect(events).not.toContain('exited')
+    expect(events).toEqual(['working', 'idle'])
+  })
+
+  it('tracks the 2.1.228 turn exactly like the 2.1.227 turn', () => {
+    const brailleTurn = CAPTURED_2_1_228_TURN.map((title) =>
+      title.replace('◐', '⠂').replace('◑', '⠐')
+    )
+    expect(trackTurn(CAPTURED_2_1_228_TURN)).toEqual(trackTurn(brailleTurn))
+  })
+
+  it('strips the spinner from stale exit titles and displayed labels', () => {
+    expect(clearWorkingIndicators('◐ Say hi in one word')).toBe('Say hi in one word')
+    expect(stripLeadingAgentTitleDecoration('◐ Claude Code')).toBe('Claude Code')
+  })
+
+  it('treats a spinner tick as decoration, not a title change', () => {
+    expect(isDecorativeAgentTitleFrameChange('◐ Say hi', '◑ Say hi')).toBe(true)
+  })
+
+  it('does not claim Gemini’s ◇ idle glyph, which neighbors the spinner block', () => {
+    expect(detectAgentStatusFromTitle('◇ Gemini CLI')).toBe('idle')
+    expect(getAgentLabel('◇ Gemini CLI')).toBe('Gemini CLI')
+  })
+})
diff --git a/src/shared/terminal-title-agent-type.ts b/src/shared/terminal-title-agent-type.ts
index 7e38a227f34..0952d96e63f 100644
--- a/src/shared/terminal-title-agent-type.ts
+++ b/src/shared/terminal-title-agent-type.ts
@@ -4,7 +4,7 @@ import {
   HERMES_AGENT_NAME_RE,
   titleHasAgentName
 } from './agent-name-token-match'
-import { isCursorAgentTitle } from './agent-title-core'
+import { containsAgentSpinnerGlyph, isCursorAgentTitle } from './agent-title-core'
 import { stripLeadingAgentTitleDecorationOrEmpty } from './agent-title-decoration'
 import { isOpenCodeNativeTitle } from './opencode-terminal-title'
 import { getWrapperTitleSegments } from './terminal-title-wrapper-segments'
@@ -96,7 +96,7 @@ export function isClaudeAgent(title: string): boolean {
   if (title.startsWith('. ') || title.startsWith('* ')) {
     return true
   }
-  if (containsBrailleSpinner(title)) {
+  if (containsAgentSpinnerGlyph(title)) {
     // Why: named non-Claude agents carry braille spinners too. Gate Cursor by its
     // identity title, not the token, so a Claude title mentioning a cursor stays Claude.
     return !isCursorAgentTitle(title) && !lower.includes('openclaude')
@@ -231,7 +231,7 @@ const TITLE_LABEL_TO_AGENT: Partial<Record<string, TuiAgent>> = {
 
 function hasGenericClaudeStatusPrefix(title: string): boolean {
   return (
-    containsBrailleSpinner(title) ||
+    containsAgentSpinnerGlyph(title) ||
     title.startsWith('✳ ') ||
     title === '✳' ||
     title.startsWith('. ') ||