The manifest linked `../zig-out/lib/libusage.a`, which is only correct when this package is the root one being built: consumed as a dependency, SwiftPM resolves the relative path against the *consumer's* directory and the link fails with "no such file or directory". The tray is the first consumer, so the path is now absolute, computed in the manifest from `#filePath` — the manifest always knows where it lives, whatever is building it. Verified both ways: `swift run --package-path swift usage-smoke tests/fixtures` here, and a throwaway package that depends on `../usage-core/swift` and prints `abi=3 providers=8`.