I investigated this further and confirmed the issue is due to a toolchain mismatch inside Xcode 26.1. Although test execution successfully generates multiple .profraw files, the coverage merge step fails. Running the merge manually using the Xcode-bundled tool results in the following error: raw profile version mismatch: Profile uses raw profile format version = 8 expected version = 10 error: no profile can be merged. The same project and test configuration generates coverage correctly on earlier Xcode versions, which strongly suggests a issue in Xcode 26.1’s coverage toolchain.