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fix: auto-enable accessibility defaults on simulator boot (#290)
On iOS 26+ fresh simulators, AccessibilityEnabled and ApplicationAccessibilityEnabled default to 0, which prevents accessibility hierarchy queries from returning any elements. Enable both flags via xcrun simctl spawn defaults write after boot_sim and build_run_sim boot the simulator. The check is idempotent (reads first, writes only if needed) and failures are logged but never propagated to avoid blocking boot.
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‎CHANGELOG.md‎

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@@ -1,5 +1,11 @@
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# Changelog
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## [Unreleased]
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### Fixed
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- Fixed `snapshot_ui` returning empty accessibility hierarchy on iOS 26+ simulators by auto-enabling accessibility defaults at simulator boot ([#290](https://github.com/getsentry/XcodeBuildMCP/issues/290)).
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## [2.3.2]
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### Fixed

‎src/mcp/tools/simulator/__tests__/boot_sim.test.ts‎

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@@ -83,6 +83,36 @@ describe('boot_sim tool', () => {
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});
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});
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it('should handle already-booted simulator and still enable accessibility', async () => {
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const executorCalls: string[][] = [];
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const mockExecutor = async (
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command: string[],
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description?: string,
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allowStderr?: boolean,
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opts?: { cwd?: string },
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detached?: boolean,
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) => {
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executorCalls.push(command);
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void description;
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void allowStderr;
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void opts;
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void detached;
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if (command.includes('boot')) {
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return createMockCommandResponse({
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success: false,
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error: 'Unable to boot device in current state: Booted',
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});
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}
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return createMockCommandResponse({ success: true, output: '0' });
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};
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const result = await boot_simLogic({ simulatorId: 'test-uuid-123' }, mockExecutor);
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expect(result.content[0].text).toBe('Simulator is already booted.');
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// Should have called accessibility write after detecting already-booted
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expect(executorCalls.some((cmd) => cmd.join(' ').includes('defaults write'))).toBe(true);
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});
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it('should handle exception with Error object', async () => {
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const mockExecutor = async () => {
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throw new Error('Connection failed');
@@ -142,7 +172,8 @@ describe('boot_sim tool', () => {
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await boot_simLogic({ simulatorId: 'test-uuid-123' }, mockExecutor);
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expect(calls).toHaveLength(1);
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// First call is the boot command; subsequent calls are from ensureSimulatorAccessibility
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expect(calls.length).toBeGreaterThanOrEqual(1);
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expect(calls[0]).toEqual({
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command: ['xcrun', 'simctl', 'boot', 'test-uuid-123'],
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description: 'Boot Simulator',

‎src/mcp/tools/simulator/boot_sim.ts‎

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@@ -7,6 +7,7 @@ import {
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createSessionAwareTool,
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getSessionAwareToolSchemaShape,
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} from '../../../utils/typed-tool-factory.ts';
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import { ensureSimulatorAccessibility } from '../../../utils/simulator-accessibility.ts';
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const baseSchemaObject = z.object({
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simulatorId: z
@@ -49,16 +50,27 @@ export async function boot_simLogic(
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const result = await executor(command, 'Boot Simulator', false);
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if (!result.success) {
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// If the simulator is already booted, still ensure accessibility defaults
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const alreadyBooted =
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result.error?.includes('Unable to boot device in current state: Booted') ?? false;
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if (alreadyBooted) {
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await ensureSimulatorAccessibility(params.simulatorId, executor);
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}
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return {
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content: [
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{
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type: 'text',
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text: `Boot simulator operation failed: ${result.error}`,
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text: alreadyBooted
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? 'Simulator is already booted.'
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: `Boot simulator operation failed: ${result.error}`,
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},
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],
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};
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}
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// Ensure accessibility defaults are enabled (required for UI hierarchy on iOS 26+)
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await ensureSimulatorAccessibility(params.simulatorId, executor);
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return {
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content: [
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{

‎src/mcp/tools/simulator/build_run_sim.ts‎

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@@ -22,6 +22,7 @@ import { determineSimulatorUuid } from '../../../utils/simulator-utils.ts';
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import { nullifyEmptyStrings } from '../../../utils/schema-helpers.ts';
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import { inferPlatform } from '../../../utils/infer-platform.ts';
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import { constructDestinationString } from '../../../utils/xcode.ts';
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import { ensureSimulatorAccessibility } from '../../../utils/simulator-accessibility.ts';
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// Unified schema: XOR between projectPath and workspacePath, and XOR between simulatorId and simulatorName
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const baseOptions = {
@@ -346,6 +347,9 @@ export async function build_run_simLogic(
346347
} else {
347348
log('info', `Simulator ${simulatorId} is already booted`);
348349
}
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// Ensure accessibility defaults are enabled (required for UI hierarchy on iOS 26+)
352+
await ensureSimulatorAccessibility(simulatorId, executor);
349353
} catch (error) {
350354
const errorMessage = error instanceof Error ? error.message : String(error);
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log('error', `Error checking/booting simulator: ${errorMessage}`);

‎src/utils/__tests__/simulator-accessibility.test.ts‎

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Original file line numberDiff line numberDiff line change
@@ -0,0 +1,101 @@
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import { describe, it, expect } from 'vitest';
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import {
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createMockExecutor,
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createCommandMatchingMockExecutor,
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createMockCommandResponse,
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} from '../../test-utils/mock-executors.ts';
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import type { CommandExecutor } from '../execution/index.ts';
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import { ensureSimulatorAccessibility } from '../simulator-accessibility.ts';
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const SIM_UUID = '12345678-1234-4234-8234-123456789012';
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describe('ensureSimulatorAccessibility', () => {
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it('should always write both accessibility flags', async () => {
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const executorCalls: string[][] = [];
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const mockExecutor = createCommandMatchingMockExecutor({
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'defaults write': { success: true, output: '' },
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});
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19+
const trackingExecutor: CommandExecutor = async (...args) => {
20+
executorCalls.push(args[0] as string[]);
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return mockExecutor(...args);
22+
};
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24+
await ensureSimulatorAccessibility(SIM_UUID, trackingExecutor);
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26+
expect(executorCalls).toHaveLength(2);
27+
expect(executorCalls[0].join(' ')).toContain('AccessibilityEnabled');
28+
expect(executorCalls[0].join(' ')).toContain('defaults write');
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expect(executorCalls[1].join(' ')).toContain('ApplicationAccessibilityEnabled');
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expect(executorCalls[1].join(' ')).toContain('defaults write');
31+
});
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33+
it('should not throw when executor throws', async () => {
34+
const mockExecutor = createMockExecutor(new Error('spawn failed'));
35+
36+
// Should not throw
37+
await ensureSimulatorAccessibility(SIM_UUID, mockExecutor);
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});
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it('should stop and not write second flag if first write fails', async () => {
41+
const executorCalls: string[][] = [];
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const callCount = { n: 0 };
43+
const mockExecutor: CommandExecutor = async (command) => {
44+
executorCalls.push(command as string[]);
45+
callCount.n++;
46+
if (callCount.n === 1) {
47+
return createMockCommandResponse({ success: false, error: 'write failed' });
48+
}
49+
return createMockCommandResponse({ success: true, output: '' });
50+
};
51+
52+
await ensureSimulatorAccessibility(SIM_UUID, mockExecutor);
53+
54+
// Both writes should be attempted even when first fails
55+
expect(executorCalls).toHaveLength(2);
56+
});
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58+
it('should not throw when first write fails', async () => {
59+
const mockExecutor = createCommandMatchingMockExecutor({
60+
'AccessibilityEnabled -bool': { success: false, error: 'write failed' },
61+
});
62+
63+
// Should not throw
64+
await ensureSimulatorAccessibility(SIM_UUID, mockExecutor);
65+
});
66+
67+
it('should pass correct simctl spawn commands', async () => {
68+
const executorCalls: string[][] = [];
69+
const mockExecutor: CommandExecutor = async (command) => {
70+
executorCalls.push(command as string[]);
71+
return createMockCommandResponse({ success: true, output: '' });
72+
};
73+
74+
await ensureSimulatorAccessibility(SIM_UUID, mockExecutor);
75+
76+
expect(executorCalls[0]).toEqual([
77+
'xcrun',
78+
'simctl',
79+
'spawn',
80+
SIM_UUID,
81+
'defaults',
82+
'write',
83+
'com.apple.Accessibility',
84+
'AccessibilityEnabled',
85+
'-bool',
86+
'true',
87+
]);
88+
expect(executorCalls[1]).toEqual([
89+
'xcrun',
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'simctl',
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'spawn',
92+
SIM_UUID,
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'defaults',
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'write',
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'com.apple.Accessibility',
96+
'ApplicationAccessibilityEnabled',
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'-bool',
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'true',
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]);
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});
101+
});

‎src/utils/simulator-accessibility.ts‎

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@@ -0,0 +1,72 @@
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import type { CommandExecutor } from './execution/index.ts';
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import { log } from './logging/index.ts';
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4+
const LOG_PREFIX = '[Simulator]';
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6+
/**
7+
* Ensure accessibility defaults are enabled on a simulator.
8+
* On iOS 26+ fresh simulators, AccessibilityEnabled and ApplicationAccessibilityEnabled
9+
* default to 0, which prevents accessibility hierarchy queries from returning any elements.
10+
*
11+
* Both flags are written unconditionally on every call — defaults write is idempotent
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* and avoids a partial-state problem where only checking one flag could skip the second.
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* Failures are logged but never propagated — accessibility setup should not block boot.
14+
*/
15+
export async function ensureSimulatorAccessibility(
16+
simulatorId: string,
17+
executor: CommandExecutor,
18+
): Promise<void> {
19+
try {
20+
const writeA11y = await executor(
21+
[
22+
'xcrun',
23+
'simctl',
24+
'spawn',
25+
simulatorId,
26+
'defaults',
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'write',
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'com.apple.Accessibility',
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'AccessibilityEnabled',
30+
'-bool',
31+
'true',
32+
],
33+
`${LOG_PREFIX}: enable AccessibilityEnabled`,
34+
);
35+
36+
if (!writeA11y.success) {
37+
log('warn', `${LOG_PREFIX}: Failed to enable AccessibilityEnabled: ${writeA11y.error}`);
38+
}
39+
40+
const writeAppA11y = await executor(
41+
[
42+
'xcrun',
43+
'simctl',
44+
'spawn',
45+
simulatorId,
46+
'defaults',
47+
'write',
48+
'com.apple.Accessibility',
49+
'ApplicationAccessibilityEnabled',
50+
'-bool',
51+
'true',
52+
],
53+
`${LOG_PREFIX}: enable ApplicationAccessibilityEnabled`,
54+
);
55+
56+
if (!writeAppA11y.success) {
57+
log(
58+
'warn',
59+
`${LOG_PREFIX}: Failed to enable ApplicationAccessibilityEnabled: ${writeAppA11y.error}`,
60+
);
61+
}
62+
63+
if (writeA11y.success && writeAppA11y.success) {
64+
log('info', `${LOG_PREFIX}: Accessibility defaults enabled for simulator ${simulatorId}`);
65+
}
66+
} catch (error) {
67+
log(
68+
'warn',
69+
`${LOG_PREFIX}: Failed to check/enable accessibility defaults: ${error instanceof Error ? error.message : String(error)}`,
70+
);
71+
}
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}

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