iOS runner build ignores -derivedDataPath when Xcode uses a custom build location #3296

Version: agent-device 0.21.19, Xcode 27 beta, macOS

What happens

When Xcode's global preference sets a custom build location, prepare ios-runner (and the first open on iOS) fails:

Failed to locate .xctestrun after build

Xcode writes the runner products relative to the runner project (dist/apple/runner/AgentDeviceRunner/Build/...) instead of the derived data path that agent-device passes. Parallel attempts can also fail with database is locked.

How to reproduce

defaults write com.apple.dt.Xcode IDEBuildLocationStyle Custom
defaults write com.apple.dt.Xcode IDECustomBuildLocationType RelativeToWorkspace
defaults write com.apple.dt.Xcode IDECustomBuildProductsPath Build/Products
agent-device prepare ios-runner --platform ios

Cause

IDEBuildLocationStyle=Custom takes precedence over -derivedDataPath for build products. Teams use this setting so that Xcode and command-line tools share one products folder.

Suggested fix

Add -IDEBuildLocationStyle=Unique to the runner build arguments, for example in RUNNER_SANDBOX_BUILD_ARGS (packages/platform-apple/src/runner/runner-cache-metadata.ts). With this argument the runner builds into the agent-device derived data path again. We verified the change locally by patching dist/src/runner-cache-metadata.js: prepare ios-runner then succeeds.

An alternative is an environment variable for extra xcodebuild arguments.