test(lua): complete grammar coverage, ABI smoke, and docs

Follow-up to 4c8937b (feat: add Lua language support) — wire Lua into
the test and doc surface the feature commit omitted.

- grammar-update-monitor: GRAMMARS registry now asserts six grammars
  (swift/kotlin/lua/c npm, dart/proto github) and that lua.hold is set;
  the vendored nan-based binding is incompatible with the pinned
  tree-sitter@0.21.1 runtime and must not auto-bump.
- language-skip: Lua is available in the default install (vendored
  grammar), unlike the optional Kotlin dependency.
- parser-loader-abi: add a Lua smoke case (root type `chunk`).
- parsing: drop the stale assertion that getLanguageFromFilename returns
  null for `module.lua` — Lua is now registered in language-detection,
  so it resolves to "lua".
- README: add the Lua row to the supported-languages table.

Verified: tsc --noEmit clean; grammar-update-monitor, language-skip,
parser-loader-abi unit suites and parsing.test.ts integration suite pass.

Co-Authored-By: Claude Sonnet 4 <noreply@anthropic.com>

README.md

@@ -580,6 +580,7 @@ GitNexus builds a complete knowledge graph of your codebase through a multi-phas
 | C          | —       | —              | ✓       | —        | ✓                | ✓                     | —      | ✓          | ✓            |
 | C++        | —       | —              | ✓       | ✓        | ✓                | ✓                     | —      | ✓          | ✓            |
 | Dart       | ✓       | —              | ✓       | ✓        | ✓                | ✓                     | —      | ✓          | ✓            |
+| Lua        | ✓       | —              | ✓       | ✓        | —                | ✓                     | —      | ✓          | ✓            |
 
 **Imports** — cross-file import resolution · **Named Bindings** — `import { X as Y }` / re-export tracking · **Exports** — public/exported symbol detection · **Heritage** — class inheritance, interfaces, mixins · **Type Annotations** — explicit type extraction for receiver resolution · **Constructor Inference** — infer receiver type from constructor calls (`self`/`this` resolution included for all languages) · **Config** — language toolchain config parsing (tsconfig, go.mod, etc.) · **Frameworks** — AST-based framework pattern detection · **Entry Points** — entry point scoring heuristics
 

gitnexus/test/integration/parsing.test.ts

@@ -935,9 +935,6 @@ describe('parsing', () => {
       const scalaLang = getLanguageFromFilename('Main.scala');
       expect(scalaLang).toBeNull();
 
-      const luaLang = getLanguageFromFilename('module.lua');
-      expect(luaLang).toBeNull();
-
       // loadLanguage throws an explicit error for a language not in the grammar map.
       // Cast through unknown to simulate a caller passing an unrecognised language key.
       await expect(loadLanguage('erlang' as unknown as SupportedLanguages)).rejects.toThrow(

gitnexus/test/unit/grammar-update-monitor.test.ts

@@ -73,19 +73,31 @@ describe('COMPATIBLE_ABI gate', () => {
 });
 
 describe('GRAMMARS registry', () => {
-  it('covers all five grammars (swift/kotlin npm, dart/proto github, c npm)', () => {
-    expect(Object.keys(mod.GRAMMARS).sort()).toEqual(['c', 'dart', 'kotlin', 'proto', 'swift']);
+  it('covers all six grammars (swift/kotlin/lua/c npm, dart/proto github)', () => {
+    expect(Object.keys(mod.GRAMMARS).sort()).toEqual([
+      'c',
+      'dart',
+      'kotlin',
+      'lua',
+      'proto',
+      'swift',
+    ]);
     expect(mod.GRAMMARS.swift.npm).toBe('tree-sitter-swift');
     expect(mod.GRAMMARS.dart.github).toContain('tree-sitter-dart');
+    expect(mod.GRAMMARS.lua.npm).toBe('tree-sitter-lua');
   });
 
-  it('marks c and kotlin report-only (holds); swift/dart/proto are auto-updatable', () => {
+  it('marks c, kotlin, lua report-only (holds); swift/dart/proto are auto-updatable', () => {
     expect(mod.GRAMMARS.c.npm).toBe('tree-sitter-c');
     expect(mod.GRAMMARS.c.hold).toBeTruthy(); // ABI-pinned: detected/reported, never auto-applied
     // kotlin is pinned to an unreleased fwcd main commit for `fun interface`
     // support (#169); npm latest (0.3.8) lacks it, so the strict-inequality
     // isNewer would auto-revert the pin without this hold.
     expect(mod.GRAMMARS.kotlin.hold).toBeTruthy();
+    // lua ships nan-based bindings incompatible with the pinned tree-sitter
+    // runtime; vendored with a rebuilt Napi binding, so the monitor must not
+    // auto-bump until the runtime upgrades and upstream migrates to Napi.
+    expect(mod.GRAMMARS.lua.hold).toBeTruthy();
     for (const k of ['swift', 'dart', 'proto']) {
       expect(mod.GRAMMARS[k].hold).toBeUndefined();
     }

gitnexus/test/unit/language-skip.test.ts

@@ -23,6 +23,10 @@ describe('isLanguageAvailable', () => {
     expect(isLanguageAvailable(SupportedLanguages.Swift)).toBe(true);
   });
 
+  it('returns true for Lua in the default install (vendored grammar)', () => {
+    expect(isLanguageAvailable(SupportedLanguages.Lua)).toBe(true);
+  });
+
   it('handles Kotlin based on optional dependency availability', () => {
     // Kotlin is now optional — result depends on whether tree-sitter-kotlin is installed
     const result = isLanguageAvailable(SupportedLanguages.Kotlin);

gitnexus/test/unit/parser-loader-abi.test.ts

@@ -112,6 +112,11 @@ const SMOKE_CASES: Record<string, SmokeCase> = {
     snippet: 'void main() {}\n',
     rootType: 'program',
   },
+  [SupportedLanguages.Lua]: {
+    language: SupportedLanguages.Lua,
+    snippet: 'local x = 1\n',
+    rootType: 'chunk',
+  },
   [SupportedLanguages.Kotlin]: {
     language: SupportedLanguages.Kotlin,
     snippet: 'fun main() {}\n',