Edge cases and divergences

The edge cases in the suite are where the contract’s exact wording gets earned. A sample:

Paths are bytes, so été.txt resolves without any Unicode normalization, and two names that differ only in case are two different files even on a filesystem that would merge them. A directory link resolves the same way through a commit and through the staged index, which sounds obvious until you know the index stores no directory entries at all and containment has to be proved from sorted path prefixes. guide.md/ with a trailing slash fails as a type mismatch while guide.md resolves right next to it. %252F in a link decodes once, to the literal text %2F, and never becomes a second path separator.

Hostile input gets the same rules with more suspicion. A document path carrying ANSI color codes, a terminal bell, and a forged CI command prints harmlessly in the human output and survives byte-for-byte in the JSON. A tree entry named with bytes that are not UTF-8 is a scanned document whose path travels as hex, not a refusal and not a silent drop, while a name the path grammar itself rejects, a backslash or a dot segment, is an UNREPRESENTABLE_PATH refusal that disclosed those exact bytes. A five-thousand-byte path is a reported limit crossing carrying both numbers. A tracked file whose object is missing from the store refuses and names the document, instead of guessing about content it cannot see.

The forge dialects pin the URL spellings the forges’ own browsers emit and nothing looser. GitLab’s legacy pre-separator form still redirects in a browser and is foreign here, as is /-/raw/; a GitLab project literally named - could never be told apart from the separator, and GitLab reserves the name anyway. Gitea’s untyped src/<ref>/ form, which some tooling still generates, is foreign because the typed src/branch/ spelling is what the forge emits; a gitea tag link is out of version scope even when its segments spell the candidate branch exactly, because no tag is a trusted ref. And the line-anchor grammars do not leak: #L10-20 is a line reference only under the gitlab dialect, #L10-L20 only under github and gitea, so the same fragment can classify differently on two forges and each classification is that forge’s truth.

The parser pin records its known differences instead of hiding them. Measured against the pinned grammar bundle and against GitHub’s own rendering, exactly one difference affects link extraction: [link[^1]](#), a footnote call inside a link label, which the pinned Rust parser does not turn into a link. A reference written that way goes unseen. That is under-reporting, the safer direction to fail, and it is written down in the corpus notes rather than waiting to be discovered. Two upstream test documents make the parser panic; the engine catches both as PARSER_PANIC, and both live in the corpus as regression tests. The GFM spec text says ftp:// should autolink where the pinned bundle and GitHub’s renderer disagree; the bundle wins, and the corpus records why.

One more, for flavor: the object store re-hashes everything with SHA-1 collision detection, and the suite proves that the public SHAttered and Shambles collision files cannot even be framed as Git objects without breaking the very property the detector checks. Reachable in code, unconstructible in practice, and tested as such.