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Isolate DerivedData per workspace to avoid conflicts with concurrent sessions #340
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on Apr 15, 2026 I've also faced the same issues.
Workaround that's working for me (multiple Claude Code sessions, one per git worktree):Set
derivedDataPathto a relative path inside each worktree root viasession_set_defaults:derivedDataPath: .build/DerivedDataBecause each worktree is a separate directory,
.build/DerivedDataresolves to a unique absolute path per session automatically — no manual hashing or env var coordination needed..build/is gitignored so it doesn't pollute the repo.Bonus issue I hit on top of this: When an MCP tool call is cancelled mid-run, the child
xcodebuildprocess orphans and keeps the DerivedData + simulator lock. A subsequent build/test call then hangs waiting for that lock. I mitigated it with a Claude CodePreToolUsehook that sweeps orphanedxcodebuildprocesses rooted under our project's.build/DerivedDatabefore each new tool call.- added a commit that references this issue
on Apr 20, 2026 - added 5 commits that reference this issue
on Apr 28, 2026 - added a commit that references this issue
on Apr 28, 2026
When multiple MCP sessions (or CLI invocations) build the same project from different clones, they all share a single flat
~/Library/Developer/XcodeBuildMCP/DerivedDatadirectory. Because xcodebuild only creates hashed per-project subdirectories when using its default DerivedData location — not when an explicit-derivedDataPathis passed — concurrent builds of the same project collide on the sharedBuild/,SourcePackages/, etc.This causes corrupted incremental builds, race conditions, and unpredictable failures when running parallel agent sessions against separate clones of the same repo.
Proposed solution: Hash the workspace/project root path into the DerivedData subdirectory, e.g.:
This mirrors how Xcode isolates DerivedData per workspace in its default location. The hash should be derived from the resolved absolute path of the workspace or project file so that different clones get different directories automatically.
Current workaround: Set a unique
XCODEBUILDMCP_DERIVED_DATA_PATHenv var orderivedDataPathsession default per session.