fix: cross-language refs, TSX JSX-prop indexing, Swift field refs, TS export signatures

[1broseidon]

Summary

Five defects surfaced by an external smoke test on real Swift / TSX / Go projects. None caught by the bench corpus because it has no Swift, no TSX with JSX-prop async fns, and no polyglot same-name symbols.

Defects fixed

Defect	Fix
cymbal investigate cross-pollutes refs across same-named symbols (Go App struct returned TSX App() callsites)	Added FindReferencesScoped/FindImpactScoped in index/store.go; Investigate/InvestigateResolved pass sym.Language. cymbal refs keeps documented best-effort name-only behavior.
TSX JSX-prop arrow fns indexed as method async (async keyword harvested as symbol name)	Split .tsx into its own language entry using tree-sitter-typescript's LanguageTSX(); route tsx through the JS classifier / refs / implements dispatch. .ts / .mts / .cts still use the plain TypeScript grammar.
Swift field/property refs returned zero	Added navigation_expression handling in extractRefSwift — captures the receiver when parent is a call_expression, the trailing member otherwise.
TypeScript export function declarations missing signature	New jsSignatureNode descends export_statement / lexical_declaration wrappers before parameter/return-type extraction. Also fixes export const fn = (x) => … arrow forms.
Swift @MainActor / modifier absorbed into protocol/class range	New swiftKeywordAnchor in nodeToSymbol anchors swift declarations to the keyword node, skipping leading attributes/modifiers.

The Go same-name method-receiver collision the report also flagged is documented as best-effort and is left as-is.

Verification

• go test ./... — all green.
• go run ./bench check — PASS, no regressions vs the 2026-04-15 baseline.
• Bench accuracy phases stay at 100% (85/85, 61/61, 10/10, 7/7).
• Repro fixtures under /tmp/cymbal-defect-repro/{polyglot,swift,ts-export} confirm each defect goes from broken → fixed end-to-end.

Files

• index/store.go — FindReferencesScoped, FindImpactScoped
• index/index.go — Investigate/InvestigateResolved pass language
• index/index_phase3_test.go — TestInvestigateScopesRefsByLanguage
• lang/registry.go — split tsx language using LanguageTSX()
• lang/lang_test.go, walker/walker_feature_test.go — updated tsx mapping
• parser/parser.go — JS dispatch routes tsx; jsSignatureNode, swiftKeywordAnchor, swiftNavigationRef
• parser/parser_feature_test.go — TSX, TS export signature, Swift field-ref, Swift attributed-protocol regressions
• CHANGELOG.md — Unreleased entries

Test plan

• go test ./...
• go run ./bench check
• Manual repro of each defect on minimal fixtures pre/post fix

[codecov-commenter]

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Codecov Report

❌ Patch coverage is 77.93103% with 32 lines in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
index/store.go	56.66%	26 Missing ⚠️
parser/parser.go	94.80%	4 Missing ⚠️
index/index.go	75.00%	2 Missing ⚠️

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