Publish immutable GML language-metadata API

[Infiland]

Parent: #817

Problem

The parser, emitter, source analysis, project collectors, and converter orchestration currently import underscore-prefixed language constants from gml_transpiler_parts/constants.py. This keeps the lexical/language-metadata boundary statically unenforceable, and many exported dictionaries are mutable at runtime.

This is the smallest coherent first slice of #817: language metadata is a leaf dependency for identifiers and tokens, and it can be made explicit without changing tokenization, preprocessing, parser behavior, or generated output.

Scope

• Keep the supported repository-internal surface in src/conversion/gml_transpiler_parts/constants.py; do not add a wrapper that merely reimports private names and do not move the roughly 1,800-line registry table.
• Publish non-underscore names for every constant currently imported across modules: precedence/operator metadata, identifier/literal/built-in sets, replacement tables, built-in variable metadata, virtual-key metadata, and every runtime-function category set.
• Add one static literal __all__ containing exactly the 64 supported public names.
• Annotate public values with Final and abstract collection types.
• Back all mapping exports with types.MappingProxyType; make RIGHT_ASSOCIATIVE a frozenset. Existing tuple/scalar/frozenset values and frozen model instances remain immutable.
• Preserve only _BUILTIN_VARIABLE_REGISTRY = BUILTIN_VARIABLE_REGISTRY as an unexported compatibility alias for the frozen top-level facade edge assigned to Slim the GML transpiler facade and enforce zero private phase imports #820.
• Migrate imports/usages in api.py, emitter.py, enum_helpers.py, expression_parser.py, gml_function_dispatch.py, identifiers.py, source_map.py, statement_parser.py, statements.py, tokens.py, utils.py, objects.py, and script_generator.py.
• Remove reportPrivateUsage=false only where this slice makes it unnecessary: all of gml_function_dispatch.py's directive and that field from identifiers.py, retaining its unused-symbol controls.

Acceptance criteria

• constants.__all__ is a statically known exact 64-name, non-private surface.
• No package or production module except the frozen top-level facade imports a private constant.
• All mapping exports reject assignment/deletion, all set exports are frozen, and built-in registry values remain frozen BuiltinVariableMetadata.
• The Inventory and freeze GML transpiler phase boundaries #815 architecture baseline changes exactly:
  • internal private edges: 209 -> 135;
  • production import edges: remain 60;
  • private production names: 22 -> 16;
  • private-usage suppressions: 17 -> 15.
• The sole remaining private constants edge is the facade import of _BUILTIN_VARIABLE_REGISTRY, still assigned to Slim the GML transpiler facade and enforce zero private phase imports #820.
• Preprocessed source, token kind/value/index/line/column, transpiled GDScript, source-map JSON, diagnostics, parser error locations, and golden outputs remain byte/value identical. No golden expectation update.
• No top-level facade exports or signatures change.

Required verification

• Run the focused Publish GML lexical and language-metadata phase APIs #817 tokenizer/transpiler/source-map/project collector suites and the golden/part-2 fixture suites.
• Run ./venv/bin/pyright --warnings, the repository Ruff command, and the full unittest suite.
• Run the exact Godot 4.7.2.stable.official.ed1daf0bf gates and pinned GameMaker LTS 2026 SNAP/Adding conversion gate.

Dependencies and order

• Inventory and freeze GML transpiler phase boundaries #815 and Extract shared typed models for GML transpiler phases #816 are complete.
• Serialize after Use the GameMaker LTS 2026 manual for generated evidence links #846 because that branch edits the same gml_function_dispatch.py import area.
• Base after Enable the complete Pyflakes Ruff rule family #850 or rerun its complete Pyflakes policy after integration.
• This child does not close Publish GML lexical and language-metadata phase APIs #817; later children still own the lexical facade/tokenization work.

[Infiland]

Reconciled before opening the implementation PR:

• This issue is the sole exact owner; no open or historical PR, remote Publish immutable GML language-metadata API #861 branch, v0.7.71 tag, or v0.7.71 release exists.
• The prior local stack was exactly Use the GameMaker LTS 2026 manual for generated evidence links #846 commit 38acf34 followed by the sole Publish immutable GML language-metadata API #861 delta e9d1537.
• After Use the GameMaker LTS 2026 manual for generated evidence links #846 shipped as v0.7.70, only that unique delta was rebased onto released main as 36e749c. Range-diff is exact and its stable patch ID remains 65bac4346cef215b0dea4ac880c39e3c2a7154e5.
• Follow-up commits update the measured architecture snapshot/comment and standalone v0.7.71 release surfaces; no Publish the typed GML lexical phase API #862, Publish typed GML expression parse, lower, and emit APIs #818, Encapsulate GML statement parsing and lowering behind a typed phase API #819, or Slim the GML transpiler facade and enforce zero private phase imports #820 work is included.
• Current focused/output/documentation matrix passes 594 tests. Pyright reports zero diagnostics; explicit full Pyflakes and normal Ruff both pass.

The PR will close only #861. Parent #817 remains open for its later ordered slices.

[Infiland]

Accepted and released through PR #871.

• Reviewed head: 0537357d3dd0e112b244ff32b4f4f5fb6a9ff0c3; merge commit: 4c351f25e1a1a92053abbbdd03796dfa53ba863c.
• Contract evidence: exact immutable 64-name metadata API; all 13 scoped consumers migrated; sole frozen facade compatibility alias retained for Slim the GML transpiler facade and enforce zero private phase imports #820; all 74 facade exports/signatures unchanged.
• Architecture evidence: internal private edges 209 -> 135 across 53 pairs; production imports remain 60; private production import edges 22 -> 16; suppressions 17 -> 15.
• Local gates: 594 focused/output/docs tests; Pyright 0 diagnostics; Ruff clean; full suite 2,861 tests OK (78 skipped); exact Godot 4.7.2 discovery 83/83; Godot validation/golden/settings 66/66; pinned SNAP/Adding LTS 2026 3/3.
• PR CI: all 17 required checks passed at the reviewed head, including full tests, exact Godot, LTS/TCC, cross-platform dependency locks/builds, and Windows durability gates.
• Release: https://github.com/Infiland/GM2Godot/actions/runs/33832094645 published https://github.com/Infiland/GM2Godot/releases/tag/v0.7.71 from the exact merge SHA; the direct tag also resolves there.
• Independent release audit downloaded 250,750,488 bytes. API digests, local SHA-256 values, and the canonical four-line SHA256SUMS all agree: Linux 34e97cff723c0d22db651c2923783c24c4f9fd65e8e299810a214ea072f7a9b8; macOS DMG b79e16ef24b83c51953c0b92e07437bcf484518c2fb0361c35a41100a9f2e7d5; macOS ZIP 9d540ea1e59c8260ae8d0da5b04daa7c87b276fdfa97a7f1d080734b6f09bee9; Windows 2059350dc7055a163db29733f9e8a56f311bd2f795c54d499a85552ec000e34c; manifest 2617568a107fa90d5bdabfc23f93e54e186ad907ace52271e18aeb148dee0383.

Two independent source/invariant reviews reproduced the immutable surface, consumer and black-box output equivalence, runtime hash, facade compatibility, and architecture counts with no remaining findings. #817 remains open for the ordered lexical/facade children.