Brummel
11e4c4624d
Enforces the `$`-in-authored-names reservation that fresh_binder (ailang-core::desugar) silently relied on. `fresh_binder` mints shadow-rename binders as <base>$<n>; its collision probe could not see an authored binder literally named <base>$<n> that binds later under the same (def, name) uniqueness key — the exact collapse class #43 closed. The `$`-for-synthetic convention (`$mp_N`, <hint>$lr_N, <base>$<n>) was held by discipline only. This makes it a lexer-enforced invariant: no Form-A identifier token may contain `$`. A one-line guard in tokenize rejects any token run containing `$` before int/float/ident classification, raising the new LexError::ReservedDollar { token, start }. It surfaces through the existing ParseError::Lex -> W::SurfaceParse -> surface-parse-error channel with zero new wiring — no new CheckError, no AST walker, no entry-point threading. Placement rationale (the load-bearing call): the threat vector is Form-A source only. The client LLM author is forbidden from emitting canonical .ail.json directly — it writes Form A exclusively; only the orchestrator hand-authors JSON in rare exceptions. So every authored identifier a hallucinating client could produce flows through the lexer. `$` is a reserved character (like parens) with no legitimate authored use in any position — unlike `.`/`/`, which DO have legitimate uses (std_list.map) and therefore live in the check layer (InvalidDefName) with AST-aware positional logic. No positional split for `$` means no walker; the lexer is the right boundary. An earlier draft put the reject in pre_desugar_validation justified by "a client could build .ail.json directly" — false under the authoring contract, so the simpler lexer reservation replaced it. Exemptions by scan order, not special-case: `$` inside string literals and comments stays legal because both are consumed by earlier branches of the scan loop, before a run is ever sliced. The six checked-in example files mentioning loop$lr_0 in comments keep parsing. Documented non-goals (honesty rule): the .ail.json deserialization path stays unguarded (the orchestrator's self-responsible channel); the fresh_binder probe-body simplification (issue Q4) is not bundled — only its now-false doc-comment is corrected to state the enforced invariant, scoped to Form-A authored identifiers. Verification (all run, all green): - 3 in-source lexer tests: reject on x$1, exemption for $ in string, exemption for $ in comment. RED confirmed pre-guard (tokenize("x$1") returned Ok([Ident]), expect_err panicked); GREEN after. - 2 integration tests (reserved_dollar_pin.rs): the reject reaches the public parse entry as ParseError::Lex(ReservedDollar); string exemption survives at parse level. - cargo test --workspace: green, 0 failed. - CLI: check on the comment-$ example (exit 0) and on the #43 shadow idiom raw_buf_int.ail (exit 0, buf->buf$1 rename minted post-parse, never re-lexed); a fresh $-binder source now rejected with the surface-parse-error diagnostic naming the token and byte offset. Spec: docs/specs/0057-reserved-dollar-in-names.md (grounding-check PASS). Plan: docs/plans/0112-reserved-dollar-in-names.md.