Every grammar error is prefixed with the tag's own letters, so the old
single-letter fragments (FCI/"I", PSVX/"X", ...) matched whatever the
grammar said: a mutation that dropped the letter and position from every
error left 9 of 11 invalid rows green. The fixture now quotes the error
text the spec demands ("unexpected letter I at position 3", "... after
valve V", "trailing O (open/closed) ...", "needs at least one function
letter after F"), and the test pins it to the single first error.
ABCDEF-106 was mispinned as a grammar rejection of "D": six letters
exceed the regex cap, so it never reached the grammar. It is now pinned
as a format rejection, and ABCDE-106 carries the "letter D at position 4"
case.
A fixture lint rejects any fragment that is a substring of its own tag
and requires grammar rows to name a letter, position or trailing rule,
so a future row cannot reintroduce the hole.
Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01FKFStjEFzpGyLq5bMpWxTd
