resolveUnderRoot joined an absolute input onto the workspace root
(/repo + /repo/x → /repo/repo/x), so files.read 404'd on a file that
exists. The Claude Config tab hands the reader a skill's absolute
SKILL.md path, which hit this. Normalize an absolute input as-is; the
existing containment check still rejects absolute paths outside the
root, so the T-102 boundary is preserved.
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
jpmschweitzerandClaude Opus 4.8
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