iOS input fails in 0.21.34+ when Apple tools resolve past a stale Xcode selection symlink #4145

agent-device 0.21.35 rejects iOS input on a Mac where Apple's tools successfully resolve the current Xcode, because an obsolete /var/db/xcode_select_link still points at a deleted installation. The same interaction succeeds with 0.21.33 on the unchanged machine.

Environment

• macOS 27.0.1, build 26A434, Apple Silicon
• Xcode 27.0, build 27A266a, installed at /Applications/Xcode.app
• iOS Simulator 27.0; tested on an iPhone 18 Pro simulator
• Node.js 22.20.0
• DEVELOPER_DIR is unset
• Tested versions: 0.21.33 passes, 0.21.35 fails

Toolchain state

The obsolete symlink exists, but its target no longer exists:

/var/db/xcode_select_link -> /Applications/Xcode-16.2.0.16C5032a.app/Contents/Developer

Apple's tools resolve the installed Xcode successfully, including with an empty environment:

$ env -i PATH=/usr/bin:/bin /usr/bin/xcode-select -p
/Applications/Xcode.app/Contents/Developer

$ env -i PATH=/usr/bin:/bin /usr/bin/xcrun --find xcodebuild
/Applications/Xcode.app/Contents/Developer/usr/bin/xcodebuild

$ xcodebuild -version
Xcode 27.0
Build version 27A266a

$ xcrun --sdk iphonesimulator --show-sdk-version
27.0

$ xcrun --sdk iphonesimulator --show-sdk-build-version
24A430

Reproduction

On a Mac with the toolchain state above, use agent-device 0.21.35's MCP server and a booted iOS simulator:

1. Call open with a named session, platform: "ios", the simulator's udid, and app: "com.apple.Preferences".
2. Call snapshot with that session and interactiveOnly: true.
3. Call press on the current snapshot ref for General, with settle: true.

open and snapshot succeed. screenshot also succeeds. press fails before dispatch:

code: COMMAND_FAILED
reason: apple_toolchain_unreadable
file: /var/db/xcode_select_link
detail: dangling selection link
dispatched: no

The error says it could not read the Xcode toolchain versions used for the Apple runner cache key, and suggests checking xcode-select -p or DEVELOPER_DIR. xcode-select -p already reports the working installation above.

Version comparison

With 0.21.33, on the same booted simulator and with no DEVELOPER_DIR override or system configuration changes, I verified:

• Open Settings and read its accessibility snapshot.
• Press General and verify that About appears on the resulting screen.
• Navigate back and close the session.

After pinning Mobile Dev to 0.21.33, I repeated the interaction through its packaged Claude server, including a screenshot and a batch command; all passed without an Xcode override.

Regression source

This comes from #3995, first included in 0.21.34. The published 0.21.34 and 0.21.35 packages contain the new identity reader; 0.21.33 does not. The live failing interaction above was tested on 0.21.35.

selectionLinkTarget() in v0.21.35 throws when the legacy symlink cannot be resolved. Its assumption that a dangling link means Apple cannot resolve a working developer directory does not hold on this machine. The corresponding test explicitly enforces that assumption.

I understand the change avoids stalled xcrun probes on hosted runners. The remaining correctness requirement is that the cache fingerprint identify the same Xcode that Apple's tools actually use. A stale legacy symlink should not block device input when the active developer directory resolves successfully.