Add ESM named fallback taxonomy artifact generator

[jununfly]

This was generated by AI during triage.

Parent

• Plan: docs/plans/2026-06-21-rust-hybrid-esm-named-binding-fallback-diagnostics-map.md
• Resolver migration tracker: Plan: Rust-hybrid resolver migration decision #296
• Architecture/performance PRD tracker: PRD: Rust-hybrid architecture and performance optimization #295
• Optimization tracker: Post-PRD optimization tracker for Rust indexing performance #165

What to build

Add a dedicated internal benchmark diagnostic that reads Rust profile ESM named fallback samples and writes JSON/Markdown taxonomy artifacts. This should not be folded into the relative import target taxonomy because it answers binding-resolution questions, not file-target questions.

The taxonomy should make the dominant fallback reasons and likely next implementation candidates visible without reading source files.

Acceptance criteria

• The generator reads a Rust profile artifact and writes JSON and Markdown artifacts.
• The output includes reason distribution, rows inspected, unavailable reason when samples are absent, and bounded examples by reason.
• The output includes a concise candidate-next-slice summary based on dominant actionable reasons.
• Tests cover normal profile input, missing sample fields, and bounded examples.
• The generator does not read source files or require a live database.

Blocked by

• Add ESM named fallback reason samples to Rust profile #363

[jununfly]

This was generated by AI during triage.

Closing as implemented in aaba106. Added scripts/rust-esm-fallback-taxonomy.mjs with JSON/Markdown artifact output, reason distribution, bounded examples, unavailable-sample handling, and candidate-next-slice summary. The generator reads profile metadata only and does not read source files or open a database.