#9313 improvement(file-parsers): parse spreadsheets on a worker thread

Summary

• XLSX.read is synchronous, so every spreadsheet parse through parseBuffer blocked the event loop for the whole parse (1.1–2s on 16–23 MB workbooks on Bun)
• Spreadsheet buffers (xlsx/xls/xlsm/xlsb/xltx/ods) now parse on a worker_threads pool running the same XlsxParser; output is identical
• Pool is bounded to one worker (in-process parses were already serialized by the sync parse, so peak workbook memory stays where it is); jobs queue, idle workers terminate after 30s
• Input bytes are copied into a fresh ArrayBuffer and transferred, so the caller's Buffer is never detached; options cross without the signal
• Abort: a queued job is dropped, a running job's worker is terminated and the call rejects with signal.reason (same value the in-process path throws)
• Errors rebuild as the same class (FileParserError with code/message/cause name+message, ZipBombError, ArchiveIntegrityError), so getFileParserErrorCode callers see no change
• Safe fallback: missing bundle, load failure, startup that never reports ready, or a crash mid-parse disables the pool for the process (one warn) and runs the job in-process exactly as before
• Enabled only for the production app server: dev/tests parse the live source, Trigger.dev workers (Node, no bundle shipped) stay in-process
• Bundle: build:xlsx-worker (bun build --target=node, builtins only, ~0.8 MB) runs in bun run build; shipped via Dockerfile COPY (fails the image build if missing) plus an outputFileTracingIncludes entry, resolved from cwd candidates like the isolated-vm worker
• Bun ignores resourceLimits, so the worker heap counts against the process exactly like an in-process parse; the bound is concurrency, not heap size
• PDF is left in-process: #9311 time-slices its loops, and pdf.js needs the native canvas binding inside the worker

Type of Change

• Improvement

Testing

• xlsx-worker-pool.test.ts builds the real bundle with bun run build:xlsx-worker and checks in-process parity (preview, complete, text-budget error, archive-guard rejection, corrupt ZIP), caller buffer intact, fallback for a missing bundle / a bundle that throws on load / a worker that exits mid-parse, abort of a running job (frees the slot of a spinning worker) and of a queued job. Each guard was reverted and its test went red
• Bun 1.4.2 event-loop gap (max timer gap during one parse):

Workbook	Mode	In-process	Worker	Output hash
16 MB	preview	1112 ms	10 ms	identical
16 MB	complete	1380 ms	8 ms	identical
23 MB	preview	1525 ms	10 ms	identical
23 MB	complete	1934 ms	14 ms	identical

• End to end through parseBuffer with NODE_ENV=production: worker 66 ms gap (cold spawn included); bundle removed → one warn, in-process, same hash; bundle replaced with a throwing file → one warn, in-process, same hash
• lib/file-parsers/ suite (316 tests), bun run lint, focused tsc on the new modules and test, check:source-conventions, check:utils, check:comment-hygiene, check:file-names, check:test-patterns, check:boundaries

Checklist

• Code follows project style guidelines
• Self-reviewed my changes
• Tests added/updated and passing (new tests pass the test-audit authoring gate)
• No new warnings introduced
• I confirm that I have read and agree to the terms outlined in the Contributor License Agreement (CLA)