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/src/langs.rs

@@ -28,12 +28,17 @@ extern "C" {
 extern "C" {
     fn tree_sitter_scala() -> *const ();
 }
+// Vendored dart grammar (build.rs-compiled C — UserNobody14 d4d8f3e; the
+// crates.io crate is a different-lineage fork; see grammars/dart).
+extern "C" {
+    fn tree_sitter_dart() -> *const ();
+}
 
 /// Languages this kernel binary can extract (reported by contractInfo;
 /// TS-side routing policy decides what actually routes).
-pub const LANGUAGES: [&str; 19] = [
+pub const LANGUAGES: [&str; 20] = [
     "typescript", "tsx", "javascript", "jsx", "java", "python", "go", "c", "cpp", "rust",
-    "csharp", "ruby", "php", "swift", "kotlin", "r", "lua", "luau", "scala",
+    "csharp", "ruby", "php", "swift", "kotlin", "r", "lua", "luau", "scala", "dart",
 ];
 
 pub fn grammar_for(language: &str) -> Option<Language> {
@@ -83,6 +88,11 @@ pub fn grammar_for(language: &str) -> Option<Language> {
         "scala" => {
             Some(unsafe { tree_sitter_language::LanguageFn::from_raw(tree_sitter_scala) }.into())
         }
+        // R7b batch 4: UserNobody14 d4d8f3e vendored C compiled in build.rs
+        // (same commit as the byte-copied tree-sitter-wasms 0.1.13 artifact).
+        "dart" => {
+            Some(unsafe { tree_sitter_language::LanguageFn::from_raw(tree_sitter_dart) }.into())
+        }
         _ => None,
     }
 }

codegraph-kernel/src/lib.rs

@@ -20,6 +20,7 @@ mod buffers;
 mod ccpp;
 mod cfnptr;
 mod csharp;
+mod dart;
 mod docstring;
 mod ids;
 mod go;
@@ -229,6 +230,7 @@ pub fn extract_file(file_path: String, content: String, language: String) -> Res
         "r" => rlang::extract(&file_path, &content).map_err(Error::from_reason)?,
         "lua" | "luau" => lua::extract(&file_path, &content, &language).map_err(Error::from_reason)?,
         "scala" => scala::extract(&file_path, &content).map_err(Error::from_reason)?,
+        "dart" => dart::extract(&file_path, &content).map_err(Error::from_reason)?,
         _ => tsjs::extract(&file_path, &content, &language).map_err(Error::from_reason)?,
     };
     Ok(ExtractBuffers {