…ent-order bug

TG-11 landed the type former, typing, evaluation and six proofs — but there
was no way to WRITE one. Zero occurrences of the constructors in lexer.mll or
parser.mly, against 4 for echo. Fully implemented and unreachable.

## Surface syntax

    warrant[k](claim, evidence)     -- at standpoint k
    evidence(w)                     -- the ONLY elimination

The standpoint is bracketed because it is an index, not an operand — the same
reading as a braid generator's subscript.

Non-factivity reaches the syntax too: there is deliberately NO keyword that
extracts the claim. `claim(w)` parses as an ordinary call to an undefined
function, never as a language form, and a test pins that distinction — if a
`Claim` form ever appears, it contradicts epi_only_yields_evidence.

No grammar conflicts.

## A SECOND copy of the statement-order bug

Writing the first epistemic program surfaced it. `def w = warrant[...]` then
`def tok = evidence(w)` failed with

    In definition 'tok': evidence requires an Epi[k, rho, tau], got Word[0]

The Word[0] is the pass-1a placeholder: `tok` was being checked BEFORE `w` had
been refined. Same root cause as #95 — `stmts := prog @ !stmts` followed by
`List.rev` on the flattened list — but in a SECOND copy, in lib/check.ml.

That copy feeds `tanglec --check` AND the LSP, so both have been analysing
programs with their statements reversed. It was not epistemic-specific:

    def e = echoClose(braid[s1])
    def r = residue(e)          -- "residue requires Echo[_, _], got Word[0]"

Any cross-definition reference to a non-Word type was mis-typed. Echo has been
broken this way for as long as the recovering path has existed. Fixed
identically: accumulate segments, flatten in order.

The test suites missed BOTH copies because they call Parser.program directly
and never exercise the recovering path.

## Tests

Parser: warrant with bracketed standpoint, evidence, TG-4 round-trip, and the
no-claim-form guard. Check: three cross-definition cases — plain, echo, and
epistemic — that would all have failed before.

examples/epistemic.tangle added and wired into the corpus gate's must-run set:
warrants at three standpoints, evidence recovery, and the echo composition
(`residue(evidence(we))`). All assertions pass.

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