Implement bounded TypeScript overload implementation tie-break

[jununfly]

This was generated by AI during triage.

Parent

• Plan: docs/plans/2026-06-21-rust-hybrid-ts-overload-implementation-tie-break.md
• Fixture prerequisite: Add guarded TypeScript overload implementation resolver fixtures #382
• Resolver migration tracker: Plan: Rust-hybrid resolver migration decision #296
• Architecture/performance PRD: PRD: Rust-hybrid architecture and performance optimization #295
• Optimization tracker: Post-PRD optimization tracker for Rust indexing performance #165

What to build

Implement the guarded production resolver tie-break for TypeScript overload/signature candidate-multiple cases in the Rust ESM named import/export path. The resolver may select an implementation candidate only when all documented guard conditions hold; otherwise it must preserve fallback behavior.

Acceptance criteria

• Direct export function overload/signature candidate-multiple resolves when exactly one implementation candidate is identified.
• Same-file export specifier function overload/signature candidate-multiple resolves when exactly one implementation candidate is identified.
• Import edge and imported usage edges target the selected implementation candidate.
• Edge metadata uses resolvedBy: "rust-esm-named-import-export-overload-implementation".
• Add esmNamedImportExportOverloadImplementationResolvedRefs, counting import refs and imported usage refs resolved by this tie-break.
• Ambient-only, declaration-file, no-implementation, type/value/namespace collision, unknown metadata, and unavailable metadata cases continue to fallback.
• No SQLite schema changes.
• Do not change one-hop re-export, default import, namespace import, package/runtime import, or multi-hop barrel behavior.

Blocked by

• Add guarded TypeScript overload implementation resolver fixtures #382

[jununfly]

This was generated by AI during triage.

Closing as implemented. Rust ESM named import/export resolution now applies the bounded overload implementation tie-break only for direct export and same-file export specifier cases when exactly one safe TypeScript implementation declaration is available. The route records resolvedBy: rust-esm-named-import-export-overload-implementation and keeps the no-go classes on fallback.

Verification: cargo test -p zcodegraph-core and targeted Rust engine CLI tests passed.