fix(api): close three retry/duplicate hazards

[mankatcheung]

Summary

Follow-up to an API idempotency audit. Conclusion: a generic idempotency-key system is not necessary for this app (small trusted client set, no adversarial/high-volume third-party callers, MCP surface is 100% read-only). But three concrete, currently-unprotected retry/duplicate hazards were found and are fixed here — each cheap, and mirroring a pattern already proven elsewhere in the codebase.

• Weekly digest duplicate-send guard. /admin/digest/send is a plain secret-gated HTTP route invoked by an external scheduler not tracked in this repo — exactly the kind of caller that may retry on a timeout/5xx. There was zero duplicate-send protection, so a retry meant every subscribed user got a duplicate digest email. Added a per-user lastDigestSentAt timestamp + a 6-day resend window, mirroring the existing reminderSentAt pattern used by follow-up reminders.
• UpdateApplicationUseCase duplicate activity-log entries. The field_updated branch logged whenever a field was present in the input, not when it actually changed — unlike the status_changed branch right next to it, which already compared against the current value. A retried/duplicate update with identical values polluted the activity timeline every time. Now compares against the pre-update snapshot (with proper Date instant comparison for followUpAt).
• Bulk-delete retry safety. BulkDeleteApplicationsUseCase used Promise.all, so retrying a partially-failed bulk-delete failed again on the already-deleted items. Switched to Promise.allSettled, treating NOT_FOUND as an idempotent no-op while other per-item failures (e.g. FORBIDDEN) still surface as before. No API contract change — still returns void / throws on real failures.

Deliberately out of scope (investigated, not fixed): MCP tools (confirmed 100% read-only), create-mutation dedup (a UI double-submit concern, not a server-side gap), and BulkUpdateApplicationsUseCase/BulkAddTagToApplicationsUseCase (no clean "already applied" no-op concept the way delete has).

Test plan

• pnpm --filter @job-finder/api test — 642 tests passing, including new coverage for all three fixes
• pnpm --filter @job-finder/api typecheck — clean
• pnpm --filter @job-finder/api lint — clean
• New Prisma migration (add_last_digest_sent_at) applied and Prisma client regenerated
• Manual smoke test of the digest guard against a live server (blocked locally by an unrelated pre-existing gap in this repo's migration history — the Document table's initial creation was never captured in a migration file, so rebuilding a fresh dev DB from migration history fails; not something to fix as part of this PR)

🤖 Generated with Claude Code

Summary by CodeRabbit

• New Features

  • Weekly digests now include a resend safeguard, preventing repeat emails within the configured window.
  • Digest delivery timestamps are recorded for improved scheduling.

• Bug Fixes

  • Bulk deletion now continues when an application is already missing, while reporting other failures.
  • Activity logs now record only genuine application field changes, including follow-up dates.

[coderabbitai]

Caution

Review failed

The pull request is closed.

ℹ️ Recent review info

⚙️ Run configuration

Configuration used: Organization UI

Review profile: CHILL

Plan: Pro Plus

Run ID: f5ab77e5-704f-443d-ba4b-ddf4e413ff1d

📥 Commits

Reviewing files that changed from the base of the PR and between 1e9e9c0 and 36566a1.

📒 Files selected for processing (14)

• apps/api/prisma/migrations/20260724205821_add_last_digest_sent_at/migration.sql
• apps/api/prisma/schema.prisma
• apps/api/src/__tests__/application/jobs/BulkDeleteApplicationsUseCase.test.ts
• apps/api/src/__tests__/application/jobs/UpdateApplicationUseCase.test.ts
• apps/api/src/__tests__/digest/SendWeeklyDigestUseCase.test.ts
• apps/api/src/__tests__/helpers/createTestDb.ts
• apps/api/src/__tests__/helpers/mocks.ts
• apps/api/src/constants.ts
• apps/api/src/domain/user/User.ts
• apps/api/src/infrastructure/db/repositories/PrismaUserRepository.ts
• apps/api/src/use-cases/digest/SendWeeklyDigestUseCase.ts
• apps/api/src/use-cases/jobs/BulkDeleteApplicationsUseCase.ts
• apps/api/src/use-cases/jobs/UpdateApplicationUseCase.ts
• apps/api/src/use-cases/ports/IUserRepository.ts

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Walkthrough

The PR adds persisted weekly digest send timestamps and resend-window checks, makes bulk deletion idempotent for missing applications, and restricts field-update activity logs to actual value changes.

Changes

Digest resend tracking

Layer / File(s)	Summary
Weekly digest resend tracking apps/api/prisma/..., apps/api/src/domain/user/User.ts, apps/api/src/use-cases/digest/..., apps/api/src/infrastructure/db/repositories/..., apps/api/src/__tests__/digest/...	Adds lastDigestSentAt to the user model, repository contract, persistence mapping, fixtures, and test database. The digest use case skips users within the six-day resend window and records successful sends.
Bulk deletion error handling apps/api/src/use-cases/jobs/BulkDeleteApplicationsUseCase.ts, apps/api/src/__tests__/application/jobs/BulkDeleteApplicationsUseCase.test.ts	Uses settled deletion results, treats NOT_FOUND as a no-op, and continues throwing other errors.
Application activity change detection apps/api/src/use-cases/jobs/UpdateApplicationUseCase.ts, apps/api/src/__tests__/application/jobs/UpdateApplicationUseCase.test.ts	Logs field_updated only for changed primitive or timestamp values and retains status_changed logging coverage.

Estimated code review effort: 3 (Moderate) | ~25 minutes

Sequence Diagram(s)

sequenceDiagram
  participant DigestJob
  participant UserRepository
  participant Mailer
  DigestJob->>UserRepository: load users and lastDigestSentAt
  DigestJob->>Mailer: send digest after resend window
  DigestJob->>UserRepository: persist send timestamp

Loading

Possibly related PRs

• mankatcheung/job-finder#60: Modifies the weekly digest use-case flow.
• mankatcheung/job-finder#76: Modifies Prisma user repository typing and mapping.
• mankatcheung/job-finder#79: Adds related bulk application deletion behaviour and tests.

Poem

A rabbit checks the digest clock,
Skips a send around the block.
Missing jobs cause no fright,
Changed fields now log just right.
Timestamps hop into their place—
Clean records leave a tidy trace.

✨ Finishing Touches

📝 Generate docstrings

• Create stacked PR
• Commit on current branch

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch fix/api-idempotency-safety

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