Narrowing has_reference to bool(import_lines) meant a UTF-8 BOM hid the import
line, since the BOM is not \s: a CLAUDE.md whose first line is @AGENTS.md failed
with 'no reference to AGENTS.md' and was told to add the line already in front of
it. Decoding is now strict too, so a non-UTF-8 adapter gets an encoding
diagnostic instead of being mangled and then graded on the mangling.
Usage errors move to exit 2. They shared exit 1 with real findings, while the
skill tells the agent to fix any non-zero exit by editing the provider file.
The whole-line import rule is kept deliberately -- accepting an inline @AGENTS.md
would also accept one inside backticks, which is the silent-drop failure the
validator exists to catch -- and the message now says so.
Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01EJJrm5YmacbwMdzZpXcoti
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