The reading exclusion floor admits two line shapes every renderer reads and its line split does not, and the excluded section travels with a nil error. A byte-order mark before an ATX heading on line 0: floorATXRe is matched against the raw line with no frontmatter.TrimBOM, so the BOM hides the heading from the verifier while a renderer drops it. And a lone carriage return: CommonMark treats a CR not followed by LF as a line ending, but the floor splits only on newline, so a CR-only document (or a lone CR inside a CRLF one) is one line to the floor and many to a renderer. Both leak at base and on fix/one-fence-rule. Each is a one-line refusal.

The reading exclusion floor admits two line shapes every renderer reads and its line split does not, and the excluded section travels with a nil error. A byte-order mark before an ATX heading on line 0: floorATXRe is matched against the raw line with no frontmatter.TrimBOM, so the BOM hides the heading from the verifier while a renderer drops it. And a lone carriage return: CommonMark treats a CR not followed by LF as a line ending, but the floor splits only on newline, so a CR-only document (or a lone CR inside a CRLF one) is one line to the floor and many to a renderer. Both leak at base and on fix/one-fence-rule. Each is a one-line refusal.

Grounds

• pursued: a BOM before an ATX or underlined excluded heading, a CR-only document and a lone CR inside a CRLF document are each refused while a plain CRLF document is admitted (TestVerifyRedactionRefusesABOMHeadingAndALoneCarriageReturn), and no tracked markdown file carries a BOM or a lone CR, so the committed corpus is unaffected; an admitted shape or a refused CRLF document would show it wrong