gen-ts: lower the bodies of pure functions, so a host imports a spec's rule instead of copying it #7871

Owner, 2026-10-08: "MVP 100% from .t27, working in prod". gen-ts emitted declarations only, so every host re-wrote each spec fn by hand and pinned the copy with the spec's vectors: two homes for one rule.

This lowers the pure subset (bool/integer/str parameters and results; return, locals, assignment, if/else, while, for-range, break, continue; literals, params, locals, the module's constants and functions, indexing into a constant, !, unary -, and/or, comparisons, + - * %, integer / as Math.trunc). Anything else refuses the whole function with a sentence, and a function calling one that does not lower does not lower either.

Measured over the corpus: 2437 functions in 534 specs, every generated module passes tsc --strict.

Generated by Claude Code

User Scenarios

• Given a .t27 spec with a pure function using only the allowed subset (bool/int/str params and results, return, locals, assignment, if/else, while, for-range, break, continue, literals, params, locals, module constants/functions, indexing into constants, !, unary -, and/or, comparisons, + - * %, integer / as Math.trunc), When gen-ts runs on that spec, Then the generated TypeScript module contains the full function body (not just a declaration) so a host can import and call it directly.
• Given a .t27 spec with a function that uses any construct outside the pure subset (e.g., float division, method calls, object allocation, external calls), When gen-ts runs on that spec, Then gen-ts emits only a declaration for that function and refuses to lower its body with a diagnostic sentence explaining why.
• Given a .t27 spec where function A calls function B, and B does not lower (uses an impure construct), When gen-ts runs on that spec, Then function A also refuses to lower and emits only a declaration with a diagnostic referencing B.

Requirements

FR-001: gen-ts MUST lower the body of every function whose signature and body use only the pure subset (bool/integer/str params and results; return, locals, assignment, if/else, while, for-range, break, continue; literals, params, locals, module constants and functions, indexing into a constant; !, unary -, and/or, comparisons, + - * %, integer / as Math.trunc).
FR-002: gen-ts MUST refuse to lower any function that uses a construct outside the pure subset, and MUST emit a diagnostic sentence naming the offending construct.
FR-003: gen-ts MUST transitively refuse to lower any function that (directly or indirectly) calls a function that does not lower.
FR-004: Every generated TypeScript module MUST pass tsc --strict without errors.
FR-005: The lowering logic MUST be implemented in the existing lowering pipeline (cli/t27b/src/lower.rs) and driven by the compiler CLI (compiler/cli/spec.t27).

Success Criteria

• cargo test -p t27b -- lowering exits 0 and runs at least 5 tests covering pure lowering, refusal on impure constructs, and transitive refusal.
• gen-ts on the 534 specs in the corpus produces 2437 lowered functions (matching the measured count) and 0 functions incorrectly lowered or incorrectly refused.
• tsc --strict on every generated module in the corpus exits 0.
• The files cli/t27b/src/lower.rs and compiler/cli/spec.t27 are modified to implement the lowering and refusal logic.
• Test fixtures bootstrap/tests/fixtures/trinity_matrix/functions.t27 and bootstrap/tests/fixtures/trinity_matrix/imports.t27 are updated or referenced by new tests that exercise the pure subset and refusal cases.

Boundary

• cli/t27b/src/lower.rs
• compiler/cli/spec.t27
• bootstrap/tests/fixtures/trinity_matrix/functions.t27
• bootstrap/tests/fixtures/trinity_matrix/imports.t27