feat(kernel): R7b Dart walker — dart module, vendored-grammar-C d4d8f3e + wasm byte-copy vendor, dart default-routed (#1386)

R7b batch 4 #4 — the FINAL R7b language (docs/design/dart-kernel-port-checklist.md
is the authoritative quirk list). The fourth vendored-grammar-C language,
with a twist: production dart resolved its wasm from tree-sitter-wasms,
whose dart dependency is an UNPINNED github:UserNobody14/tree-sitter-dart —
a routine dependency update would have silently changed dart's grammar.
This PR byte-copies the shipping 0.1.13 artifact into src/extraction/wasm/
(VENDORED_WASM_LANGS += dart) and compiles the same-commit (d4d8f3e337d8)
parser.c/scanner.c in the kernel — table identity proven by the
kernel-grammar-parity row. crates.io tree-sitter-dart is the nielsenko
fork (different lineage) — rejected.

The center of gravity is THE SIBLING-BODY DOUBLE-WALK, reproduced
bug-for-bug: dart attaches every function/method body as a NEXT SIBLING of
its signature, and the TS walkers consume each body TWICE — once via
resolveBody (attributed to the function/method) and once via the enclosing
generic walk (attributed to the file/class). Duplicate local-function
nodes with the SAME id under different parents, duplicated
calls/instantiates refs, and file/class-attributed fn-ref twins all emit
in the exact observed interleave (a dedicated fixture pins the
duplicate-id rows; the bloc kind-census spot-check pins the counts).

Also preserved (probe-pinned): the extractBareCall selector matrix (the
first callTypes=[] language — cascades completely invisible, `?.` encodes
like `.`, the `ConfigT.load()` calls+references double emission with no
callee-of-call skip, capitalized-chain `Foo.create().run` re-encode,
const-object callee names); the constructor hooks (unnamed ctor skipped,
named ctors/factories renamed to the CTOR name with the class as
returnType, `@override (T) m()` record-misparse rescued by class-name
validation); operator methods minting `method "<anonymous>"`;
static_final_declaration constants via the visitNode hook while instance
fields mint NOTHING; the prefixed-return-type prefix bug (`other.OtherClass
f()` → returnType `other`); enum `with` mixins silent vs `implements`
working; anonymous extensions named after the ON type; deferred imports
invisible; named-argument callbacks NOT fn-ref-captured (the Flutter
`onPressed:` idiom — future accuracy PR, TS-side first); `async*`/`sync*`
NOT async; value-refs with the LIVE dart sibling-body pull and the
`$X`-vs-`${X}` interpolation asymmetry; dartdoc kept in all three comment
forms with the annotation-broken chain.

Gates: parity sweeps first-run 0-diff on shelf/bloc/flutter — 5,815 clean
files byte-parity, deferrals 10/21/1341 ≈ the survey's 10/21/~1340
(both-arm grammar reality: empty object patterns — the sealed-class
idiom — and unnamed `library;` dominate; --max-deferral 0.3); full-init
dumps byte-identical ×3 (shelf 7,959 / bloc 40,026 / flutter 1,855,319
dump lines); bloc per-kind node census identical across arms (the
double-walk duplicate rows survive the store identically);
kernel-dart-parity suite (7 fixtures + in-memory CRLF variants +
double-walk duplicate-id pin + generated-file skip pin + two defer pins);
full suite 2,688 green ×2 with CODEGRAPH_KERNEL_EXPECT=1.
DEFAULT_ROUTED += dart (20 langs — R7b COMPLETE).

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

codegraph-kernel/build.rs

@@ -60,4 +60,28 @@ fn main() {
     scala.flag_if_supported("-utf-8"); // msvc
     scala.compile("tree-sitter-scala");
     println!("cargo:rerun-if-changed=grammars/scala");
+
+    // Dart grammar — vendored C (fourth vendored-grammar-C language): the
+    // production wasm is the tree-sitter-wasms 0.1.13 artifact, whose dart
+    // dependency is an UNPINNED github:UserNobody14/tree-sitter-dart — the
+    // vendored wasm byte-copy (src/extraction/wasm/) plus these same-commit
+    // sources kill that hazard. crates.io tree-sitter-dart is the nielsenko
+    // FORK (different lineage) — rejected. Sources are
+    // UserNobody14/tree-sitter-dart master@d4d8f3e337d8 (dart checklist
+    // §Grammar prep):
+    //   parser.c  5a42b47abb4d494f125dbdee9138979248041689b1aa36355550fa3e28dcb8b8
+    //   scanner.c 07a7b7818b175e9460523e705dd88d20f7b5141bac95c593d4426e6d52284996
+    // scanner.c is load-bearing: string-template char classes and /** */ doc
+    // comments are external tokens.
+    let mut dart = cc::Build::new();
+    dart.include("grammars/dart");
+    dart.file("grammars/dart/parser.c");
+    dart.file("grammars/dart/scanner.c");
+    dart.flag_if_supported("-Wno-unused-parameter");
+    dart.flag_if_supported("-Wno-unused-but-set-variable");
+    dart.flag_if_supported("-Wno-trigraphs");
+    dart.flag_if_supported("-Wno-unused-function");
+    dart.flag_if_supported("-utf-8"); // msvc
+    dart.compile("tree-sitter-dart");
+    println!("cargo:rerun-if-changed=grammars/dart");
 }