fix(scala): resolve chained static-factory/apply calls Foo.create().bar() (#750) (#761)

Ports the #645 (C++) / #608 (PHP) chained-receiver mechanism to Scala. A call
whose receiver is itself a call — `Foo.create().bar()` (companion factory),
`Builder(cfg).bar()` (case-class apply), or a fluent chain — used to drop the
receiver to a bare `bar`, which name-matched a same-named method on an unrelated
type. The most common wrong edge was a stdlib `Option`/`Iterator` `.map`/`.flatMap`/
`.foreach` mis-attributed onto the project's own same-named class.

- scala.ts: `getReturnType` reads the `return_type` field — generic `List[Foo]`
  → container `List`, qualified `pkg.Foo` → `Foo`, `this.type` left undefined.
- tree-sitter.ts: re-encode `Foo.create().bar` when the inner call's receiver chain
  starts with a capital (companion factory / case-class apply); instance chains
  (`list.map().filter()`) stay bare.
- name-matcher.ts: `scala` joins the dotted-chain gate + CONSTRUCTS_VIA_BARE_CALL
  (case-class `apply` constructs the class); resolveMethodOnType validates, so a
  non-conventional `apply` returning another type yields no edge, not a wrong one.
- index.ts: `scala` joins CHAIN_LANGUAGES so trait-inherited methods resolve via
  the conformance second pass.

Validation: 4 synthetic tests (factory+decoy, case-class apply, trait conformance,
absent-method safety). Real-repo A/B on gatling (750 Scala files): +14 / -59 unique
edges — all corrections. The +14 are retargets (e.g. `HttpProtocolBuilder(cfg).baseUrl`
now resolves to HttpProtocolBuilder::baseUrl, not the same-named private BaseUrlSupport
helper); the -59 are wrong edges removed (stdlib Option/Iterator monad calls
mis-tied to the project's Validation::*, self-loops, decoy collisions) — zero genuine
factory chains dropped (verified: gatling has no real Validation.success().map() chains).
db stable at 40 MB. EXTRACTION_VERSION 12→13. Full suite green.

Co-authored-by: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

src/extraction/extraction-version.ts

@@ -21,4 +21,4 @@
  * turns the re-index hint into noise — keep it honest (see CLAUDE.md, "Honesty
  * in the product is load-bearing").
  */
-export const EXTRACTION_VERSION = 12;
+export const EXTRACTION_VERSION = 13;

src/extraction/languages/scala.ts

@@ -44,6 +44,28 @@ function emitScalaTypeRefs(typeNode: SyntaxNode, fromId: string, ctx: { addUnres
   }
 }
 
+/**
+ * Capture a Scala method's declared return type as a bare type name, for the
+ * chained static-factory / fluent call mechanism (#750). `def create(): Bar`
+ * yields `Bar`; a generic `List[Bar]` yields its base `List` (the method is on
+ * the container, not the element); a qualified `pkg.Bar` yields `Bar`. A
+ * singleton self-type (`this.type`, the fluent-builder idiom) is left undefined
+ * — its type can't be recovered here, so the chain falls through rather than
+ * inferring a wrong receiver.
+ */
+function extractScalaReturnType(node: SyntaxNode, source: string): string | undefined {
+  const rt = node.childForFieldName('return_type');
+  if (!rt) return undefined;
+  const raw = getNodeText(rt, source).trim();
+  if (raw.startsWith('this.')) return undefined; // `this.type` singleton — unhandled
+  const base = raw
+    .replace(/\[[^\]]*\]/g, '') // strip generic args: List[Bar] → List
+    .replace(/\s+/g, '');
+  const last = base.split('.').pop(); // qualified pkg.Bar → Bar
+  if (!last || !/^[A-Za-z_]\w*$/.test(last)) return undefined;
+  return last;
+}
+
 function extractVisibility(node: SyntaxNode): 'public' | 'private' | 'protected' {
   for (let i = 0; i < node.namedChildCount; i++) {
     const child = node.namedChild(i);
@@ -77,6 +99,7 @@ export const scalaExtractor: LanguageExtractor = {
   bodyField: 'body',
   paramsField: 'parameters',
   returnField: 'return_type',
+  getReturnType: extractScalaReturnType,
   interfaceKind: 'trait',
 
   classifyClassNode: (node: SyntaxNode) => {

src/extraction/tree-sitter.ts

@@ -2530,7 +2530,8 @@ export class TreeSitterExtractor {
                 this.language === 'kotlin' ||
                 this.language === 'swift' ||
                 this.language === 'rust' ||
-                this.language === 'go') &&
+                this.language === 'go' ||
+                this.language === 'scala') &&
               receiver &&
               receiver.type === 'call_expression'
             ) {
@@ -2572,6 +2573,11 @@ export class TreeSitterExtractor {
                 // only drop the edge. C/C++ re-encode any inner.
                 if (this.language === 'rust') reencode = innerFn?.type === 'scoped_identifier';
                 else if (this.language === 'go') reencode = innerFn?.type === 'identifier';
+                // Scala: only a companion-factory / case-class-apply chain whose
+                // receiver chain starts with a capitalized type (`Foo.create().bar()`,
+                // `Foo(args).bar()`). An instance chain (`list.map().filter()`) has a
+                // lowercase receiver whose type we can't recover — leave it bare.
+                else if (this.language === 'scala') reencode = /^[A-Z]/.test(innerCallee);
                 else reencode = !!innerCallee;
               }
               calleeName = reencode ? `${innerCallee}().${methodName}` : methodName;