Cap concurrency on two services that were fanning out unbounded
requests to external systems:
1. email-compose.service.ts — attachment resolution. User attaches
20 files → 20 simultaneous S3/MinIO GETs + 20 buffers in heap.
Now capped at 4 concurrent reads; peak memory bounded by
4 × max-attachment-size regardless of attachment count.
2. document-signing-emails.service.ts — sendSigningCompleted fanned
out one SMTP send per recipient simultaneously. A Sales Contract
with 10 recipients (client + 5 sellers + 4 witnesses) hit SMTP
provider connection limits (Mailgun/SES/Postmark all cap concurrent
connections in the single digits) and dropped overflow silently.
Now capped at 3 concurrent sends.
Both use `pLimit(N)` from the Sindre Sorhus suite — well-tested at
scale, ~1kb gzip per service. Pattern is established for the
remaining audit-flagged mass-op services (brochures, backup, GDPR
export) to adopt as those files are touched.
Verified: tsc clean, vitest 1293/1293 pass.
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
Matt
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