0.5.1: roots that overlap are refused, and a file root globs nothing beside it - #14
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…beside it The design record this implements states that overlapping roots are refused, and 0.5.0 shipped without the check. A file reachable from two roots has two namespace paths, and which one it got depended on the order of the list; it was also read twice and merged with itself, so the entry looked like two implementations agreeing. A misconfiguration that produces a plausible result is worse than one that stops, and this is the shape of defect where a requirement folded into a larger change disappears when that change ships. The re-run glob is now registered only for a directory root. A single file is its own root and its parent directory is not part of it, so globbing that parent made an unrelated file beside it an input to the build program. A root that is the package root itself no longer produces a `./**/*` pattern. A CI step covers the refusal: the fixture is perturbed to name `src` beside `src/kernels`, and the build fails naming both roots.
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2026-09-08-island-boundary-names.md. The design record states that overlapping roots are refused, and 0.5.0 shipped without the check -- a requirement folded into a larger change, gone when that change shipped.What was missing
roots = { "src/kernels", "src" }was accepted. A file reachable from both has two namespace paths, and which one it got depended on the order of the list; it was also read twice and merged with itself, so the entry looked like two implementations agreeing rather than one file counted twice. The result was plausible, which is worse than a refusal.And one imprecision beside it
The re-run glob was registered from a root's base directory, which for a single-file root is that file's parent. Globbing the parent made an unrelated file sitting beside it an input to the build program. The glob is now registered only for a directory root, and a root that is the package root itself no longer produces a
./**/*pattern.Criteria
A new step perturbs the fixture to name
srcbesidesrc/kernelsand asserts the build fails naming both roots. The ten existing island steps were re-run locally against the released mcpp 2026.9.8.1 and all pass unchanged.The floor does not move.