…ertion

The trefoil assertion corrected in #95 was not an isolated slip. Auditing
whether the conformance corpus actually RUNS — the gate only ever checked that
it PARSED — turned up a second mathematically false claim of exactly the same
kind, plus one genuine unimplemented feature.

## The second false assertion

conformance/valid/v16_close_mirror_reverse.tangle asserted

    assert reverse(braid[s1, s2]) == braid[s2, s1]

`reverse` reverses the word AND negates every exponent — it yields the INVERSE
braid, so reverse(s1 s2) = s2^-1 s1^-1. Disproved by invariant:
writhe(reverse(braid[s1,s2])) = -2 while writhe(braid[s2,s1]) = +2, and writhe
is invariant under the braid relations. Corrected.

Two independent authors made the identical mistake, which is a documentation
failure, not carelessness: FORMAL-SEMANTICS.md described the operation as
"reverse word", which reads as order-only. Now stated as an identity —
reverse(w) = w^-1, i.e. reverse(g1 … gn) = gn^-1 … g1^-1 — with the contrast
against `mirror` (which negates IN PLACE) spelled out, and with the writhe
argument recorded so the next reader can check it themselves.

## The systemic fix

`scripts/check-corpus.sh` now EVALUATES conformance/valid, not just parses it.
Parsing was never enough: a program can parse perfectly and assert something
false. Both bad assertions survived precisely because nothing ran them.

Verified by reintroducing the exact false assertion — the gate catches it
(exit 1, "parses but does not evaluate") — and by restoring it (exit 0).

## The genuine gap

conformance/valid/v09_twist.tangle uses `(~a)` to twist a named strand inside
a weave. spec/grammar.ebnf says "In weave context: (~a) twists named strand
a", but infer_expr rejects any strand name used as an expression, so the
construct is specified and unimplemented. Recorded in the new
CONFORMANCE_KNOWN_UNRUNNABLE manifest list rather than papered over, and
raised as its own issue.

## Regression tests

Four pinning `reverse`'s semantics, chosen so they cannot pass vacuously:
that it is NOT order-reversal, that applying it twice is the identity (only
true if it really inverts), that it negates writhe, and the contrast with
`mirror`. Suites 112 -> 116; all green.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>