feat(kernel): R7b Kotlin walker — kotlin module, vendored-grammar-C build, kotlin default-routed (#1382)

Sixth R7b port — the T1½ batch finale. Checklist-first recipe
(docs/design/kotlin-kernel-port-checklist.md, 1,121 lines, dist-extractor
ground truth); parity passed FIRST RUN on all three repos.

THE NOVEL MECHANISM — vendored-grammar-C (the §4 tracker's prescription,
first use): the crates.io tree-sitter-kotlin 0.3.8 pins `tree-sitter >= 0.21,
< 0.23` (the kernel links 0.25) and tree-sitter-kotlin-ng is a DIFFERENT
grammar (8 fields vs 0, renamed kinds — extractor-breaking), so no crate dep
is possible. The fwcd 0.3.8 tag's sha-matched parser.c + scanner.c are
vendored into codegraph-kernel/grammars/kotlin and compiled by build.rs (cc),
exposed via tree-sitter-language::LanguageFn. The wasm re-vendor is
behavior-NEUTRAL (0 CST/error disagreements across 1,984 gate-repo files;
old-vs-new full-init dumps byte-identical ×3) — a reproducibility re-vendor,
ABI stays 14.

Walker firsts: extension-function receivers (getReceiverType →
`WidgetK::extend` QN OVERRIDE with no package prefix, the qualified-receiver
`com::qext` first-segment bug, and the owner-contains fallback that excludes
`interface` kinds and is source-order dependent) and extractModifiers
(expect/actual platform modifiers → the node DECORATORS wire field on every
created node — the KMP synthesizer's feed, incl. `actual typealias`).
Preserved bug-for-bug: the FIELD_COUNT-0 dead cluster (no signatures, ZERO
type-annotation refs), hook-consumed property initializers emitting nothing
(incl. `by lazy {}`), the bodiless-vs-bodied class header asymmetry, enum-
entry bodies being invisible, KDoc never a docstring AND chain-breaking,
comment-gluing into import/package extents, `@Anno(args)` emitting nothing
while `@Marker` decorates, zero instantiates refs, the paren-then-lambda
`trailing()` garbage callee, text-includes visibility/suspend false
positives, and the packaged-file value-ref target drop. The fun-interface
misparse-recovery hook is DEFER-SHIELDED (every such file has_error) and
deliberately not ported. The swift-sweep lesson pre-applied: the shared
`assignment` shadow-prune case is implemented alongside the
property_declaration case.

Gates: sweeps 0-diff okio 299/322, okhttp 531/580, kotlinx.coroutines
1031/1082 (deferrals exactly the predicted 23/49/51 — both-arm grammar
reality incl. PHANTOM hasError files with complete CSTs; the kernel trusts
the flag); full-init dumps byte-identical ×3 (46.5k/108.9k/92.3k lines); KMP
expect/actual synthesis IDENTICAL across arms (412 edges on
kotlinx.coroutines — the tracker's KMP validation); kernel-kotlin-parity
suite (torture reflowed off the phantom shapes + .kts script + CRLF variants
+ fun-interface and phantom defer pins) + kotlin grammar-parity row (the
C-build ↔ wasm table identity proof); full suite 2,633 green ×2 under
CODEGRAPH_KERNEL_EXPECT=1. DEFAULT_ROUTED += kotlin (15 langs).

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

codegraph-kernel/build.rs

@@ -1,3 +1,23 @@
 fn main() {
     napi_build::setup();
+
+    // Kotlin grammar — vendored C, compiled here instead of a crate dep: the
+    // crates.io tree-sitter-kotlin 0.3.8 pins `tree-sitter >= 0.21, < 0.23`
+    // (the kernel links 0.25) and tree-sitter-kotlin-ng is a DIFFERENT
+    // grammar (8 fields vs 0, renamed kinds — extractor-breaking). Sources
+    // are the fwcd 0.3.8 tag's checked-in generated artifacts, sha-matched
+    // against the crates.io tarball (kotlin checklist §Grammar prep):
+    //   parser.c  54104a7ef1555c265b746c790e0f8bb953cc17806e9df0c3af82f7f62c06a70a
+    //   scanner.c 27f73337ec357fc341fa57538f34c14277b0346980c3405dc30beab6202ec6d0
+    // Flags crib the tarball's own bindings/rust/build.rs.
+    let mut c = cc::Build::new();
+    c.include("grammars/kotlin");
+    c.file("grammars/kotlin/parser.c");
+    c.file("grammars/kotlin/scanner.c");
+    c.flag_if_supported("-Wno-unused-parameter");
+    c.flag_if_supported("-Wno-unused-but-set-variable");
+    c.flag_if_supported("-Wno-trigraphs");
+    c.flag_if_supported("-utf-8"); // msvc
+    c.compile("tree-sitter-kotlin");
+    println!("cargo:rerun-if-changed=grammars/kotlin");
 }