feat(kernel): R1 scaffold — napi-rs extraction kernel, buffer contract, routing + fallback, grammar-parity CI

Phase 0 of the Rust extraction-kernel migration (docs/design/
rust-kernel-migration-plan.md, now checked in with §3a recording the
shipped state):

- codegraph-kernel/ napi-rs crate: extractFile(path, content, language)
  → five flat buffers (meta/nodes/edges/refs/arena), one JS boundary
  crossing per file. Node ids computed Rust-side, byte-identical to
  generateNodeId (pinned by test vector). Reserved per-node metrics slot
  for the Arc 3.2 code-metrics work.
- Generic .scm-driven emitter (@def.<kind>/@name/@ref.<kind> captures,
  byte-range scope stack → ::-joined qualified names, contains edges,
  refs attributed to the innermost enclosing symbol). Seed TS/JS queries
  are smoke-level; R2 replaces them with the full port.
- Routing seam in extractFromSource with per-file wasm fallback.
  DEFAULT_ROUTED is empty — no behavior change until a language passes
  its equivalence gate (R3). Dev opt-in: CODEGRAPH_KERNEL_LANGS. Kill
  switch: CODEGRAPH_KERNEL=0. Loader verifies ABI + kind tables before
  routing; EDGE_KINDS became a runtime array because kind order is now
  wire contract.
- Grammar-source parity: vendored TS/TSX/JS wasm grammars built from the
  exact crate revisions (tree-sitter-typescript v0.23.2,
  tree-sitter-javascript v0.25.0, checked-in parser.c, ts-cli 0.25.10) —
  the tree-sitter-wasms builds were 2023-era, which the new
  kernel-grammar-parity test caught on day one. Production TS/JS parsing
  gets 2.5 years of grammar fixes; full suite green (2456 tests).
- Build/release wiring: scripts/build-kernel.sh + npm run build:kernel;
  release.yml kernel prebuild matrix (continue-on-error — the kernel is
  optional everywhere, bundles fall back to the wasm path); bundles stage
  lib/kernel/codegraph-kernel.node; release job runs the kernel suites
  with CODEGRAPH_KERNEL_EXPECT=1.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

codegraph-kernel/Cargo.toml

@@ -0,0 +1,32 @@
+[package]
+name = "codegraph-kernel"
+version = "0.1.0"
+edition = "2021"
+license = "MIT"
+publish = false
+description = "Native extraction kernel for CodeGraph — tree-sitter parse+extract with one JS boundary crossing per file"
+
+[lib]
+crate-type = ["cdylib"]
+
+[dependencies]
+napi = { version = "3", default-features = false, features = ["napi8"] }
+napi-derive = "3"
+tree-sitter = "0.25"
+streaming-iterator = "0.1"
+sha2 = "0.10"
+
+# Grammars — MUST stay revision-matched with the wasm grammars the fallback
+# path loads (tree-sitter-wasms npm package / src/extraction/wasm/). The
+# kernel-grammar-parity test asserts node-kind-table equality at test time;
+# bump these together with the wasm side or that gate fails.
+tree-sitter-typescript = "0.23"
+tree-sitter-javascript = "0.25"
+
+[build-dependencies]
+napi-build = "2"
+
+[profile.release]
+lto = true
+codegen-units = 1
+strip = "symbols"