feat(kernel): R7b Lua+Luau walker — one lua module, vendored-grammar-C lua v0.4.1, tree-sitter-luau 1.2.0 pin, both default-routed (#1384)

R7b batch 4 #2 (docs/design/lua-luau-kernel-port-checklist.md is the
authoritative quirk list). ONE walker for both dialects (ccpp precedent) —
the differences are exactly four: luau's type_definition aliases, the
`export `-slice isExported hook, the return-type signature suffix, and the
grammar handle.

Grammar prep is kernel-side only, no wasm change: lua is the SECOND
vendored-grammar-C language (the vendored wasm is the v0.4.1 tag, a revision
not on crates.io — tag artifacts compiled via build.rs, shas pinned); luau
is a plain crate pin =1.2.0 whose tarball is sha-identical to the tag (the
swift tag≠crate divergence does not recur). Grammar-parity rows replace the
bump gate entirely.

Preserved bug-for-bug (all probe-pinned): the require/visitNode-hook
ASYMMETRIES (top-level requires — including inside top-level if/for/while —
mint import nodes while the identical body-level statement emits
`calls "require"`; top-level `local x = foo()` initializers are invisible
while global `x = foo()` calls emit), the BFS string-win inside require args
(`require(script:WaitForChild("Kid"))` → import Kid) and Roblox instance
paths, receiver-QN methods (`M.sub.deep::chained`, `_G::installed`,
stack-QN nested globals like `render::leakedGlobal`), the raw-text callee
world (colon forms with `self` never stripped, bracket callees,
newline-glued chains byte-verbatim, the `(handler)` paren-conversion),
LUA_SPEC function-as-value capture with the `M.cb = cb` param-storage skip
and first-occurrence dedupe, LuaDoc `---` keeping a leading `- ` plus
`--!strict` joining docstring chains (block-comment docstrings keep interior
CRLF bytes), variable nodes at the IDENTIFIER with positional value pairing,
duplicate same-(kind,name,line) ids, and the lua↔luau isExported wire
divergence (lua functions: flag absent; luau functions: present-false;
methods: absent in both; variables: present-false in both; `export type`:
true).

Gates: parity sweeps first-run 0-diff on kong/lazy.nvim/lua-resty-core
(lua) + lune/Fusion (luau) — 1,734 clean files byte-parity, deferrals
1/0/0/3/8 matching the survey's both-arm predictions exactly (kong's 1 = a
deliberately invalid fixture; luau's = grammar-inherent generic type packs
and default type params); full-init dumps byte-identical kernel-vs-wasm ×4
(kong 157,650 dump lines); kernel-lua-parity suite (both torture fixtures +
in-memory CRLF variants + glue-chain, duplicate-id, and cross-dialect defer
pins + kernel-arm wire-flag pins); full suite 2,647 green ×2 with
CODEGRAPH_KERNEL_EXPECT=1. DEFAULT_ROUTED += lua, luau (18 langs).

Co-authored-by: Claude Fable 5 <noreply@anthropic.com>

codegraph-kernel/build.rs

@@ -20,4 +20,23 @@ fn main() {
     c.flag_if_supported("-utf-8"); // msvc
     c.compile("tree-sitter-kotlin");
     println!("cargo:rerun-if-changed=grammars/kotlin");
+
+    // Lua grammar — vendored C (second vendored-grammar-C language): the
+    // vendored wasm is tree-sitter-grammars/tree-sitter-lua v0.4.1 (tag
+    // 816840c592), which is NOT on crates.io (only 0.1/0.2/0.5 exist; 0.5.0
+    // adds Lua-5.5 `global` — a future bump with its own gate). Sources are
+    // the v0.4.1 tag's checked-in generated artifacts, sha-recorded in the
+    // lua-luau checklist §Grammar prep:
+    //   parser.c  b34a362e43f0311f405721f3089e94f97f31da403b154d456d093e64609a4081
+    //   scanner.c 35bbd630b5a7421d46d2e91185eeea09bf78565d44cb676b63ca20d0f1b54bbd
+    let mut lua = cc::Build::new();
+    lua.include("grammars/lua");
+    lua.file("grammars/lua/parser.c");
+    lua.file("grammars/lua/scanner.c");
+    lua.flag_if_supported("-Wno-unused-parameter");
+    lua.flag_if_supported("-Wno-unused-but-set-variable");
+    lua.flag_if_supported("-Wno-trigraphs");
+    lua.flag_if_supported("-utf-8"); // msvc
+    lua.compile("tree-sitter-lua");
+    println!("cargo:rerun-if-changed=grammars/lua");
 }