feat(kernel): R7b Scala walker — scala module, vendored-grammar-C master@0aca5d0a6f, scala default-routed (#1385)

R7b batch 4 #3 (docs/design/scala-kernel-port-checklist.md is the
authoritative quirk list). The third vendored-grammar-C language and the
biggest grammar in the tree (35MB parser.c): the vendored wasm is
tree-sitter/tree-sitter-scala master@0aca5d0a6f — a post-v0.26.0 generation
sync that is not a release (the 0.26.0 crate is 30 states BEHIND, so a
crate pin would be a silent downgrade). NO wasm change: production has
parsed with this exact revision since #91 — the kernel-grammar-parity row
(ABI 15, 26,650 states, 32 fields, id-by-id tables) is the whole alignment
proof.

Preserved bug-for-bug (all probe-pinned): the leak-through asymmetries —
extension methods mint NO nodes (first def's body calls leak to the
enclosing scope, later defs invisible, and the braced form resolves its
body field to the `{` TOKEN via first-match-wins field lookup → whole
extension invisible); anonymous `new T { … }` template_body members leak to
the enclosing scope (findAnonymousClassBody misses template_body); the
bodied-vs-bodiless class asymmetry (bodiless headers walk class_parameters
→ default-value calls emit FROM the class; bodied ones never see them) —
plus first-segment import names (`import com.example.C` → `com`), the
val/var hook keyed on the enclosing-definition NODE TYPE (object vals →
constants/value-ref targets, class/trait/enum/given vals → fields) with
consumed initializers, every def routed through extractMethod with the
top-level function fallback, nested defs in bodies minting NOTHING (the
inverse of kotlin) while body-local classes extract fully, curried
signatures keeping only the FIRST parameter list (type params win the
`parameters` field), enum cases positioned at the CASE node with invisible
params/extends tails, extends with-chains via scalaBaseTypeName,
`@deprecated(args)` decorates, the #750 capitalized-chain re-encode
(`WidgetS.create().render`), literal-receiver silence, static-member reads
AND writes, infix invisibility, `derives` silence, scaladoc retention with
the CRLF `\r` pin, full value-reference machinery (shadow prune, last-wins
same-name targets, `$X`/`${X}` interpolation reads), and SCALA_SPEC
fn-refs (bare ids + postfix eta unwrap + varinit, var-init non-capture).

Gates: parity sweeps first-run 0-diff on os-lib/cats/scala3-compiler-src/
scala3-library-src — 1,935 clean files byte-parity, deferrals 0/15/57/116
matching the survey's predictions exactly (scala-3's PHANTOM hasError
files — flag-true, zero ERROR nodes, capture-checking `^` — defer on the
FLAG); full-init dumps byte-identical ×3 (os-lib, cats, scala3 whole-repo
950,889 dump lines); kernel-scala-parity suite (9 fixtures + 9 in-memory
CRLF variants incl. Scala-3 indentation through the external scanner +
phantom/real-error defer pins + first-segment/namespace/value-ref pins);
full suite 2,669 green ×3 with CODEGRAPH_KERNEL_EXPECT=1
(kernel-scaffold's stays-wasm example moved scala → pascal).
DEFAULT_ROUTED += scala (19 langs).

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

src/extraction/kernel/index.ts

@@ -94,6 +94,15 @@ const DEFAULT_ROUTED: ReadonlySet<Language> = new Set<Language>([
   // packs, default type params) — a JUMP past ~10% is the bug signal.
   'lua',
   'luau',
+  // R7b batch 4 (2026-07-20): parity swept 0-diff on os-lib/cats + scala3
+  // compiler/src + library/src + full-init dump-diffs byte-identical.
+  // Error incidence is bimodal: mainstream Scala-2-style repos ~0-2%
+  // (os-lib 0%, cats 1.8%) but scala-3-frontier code runs 10-18% with
+  // PHANTOM-dominated error sets (hasError=true, zero ERROR nodes —
+  // capture-checking `^` types; defer on the FLAG). Sweeps over
+  // scala3-style repos use --max-deferral 0.3 (swift precedent); a
+  // deferral JUMP on cats/os-lib-style code is the bug signal.
+  'scala',
 ]);
 
 /**