fix(mailer,audit): propagate send and write failures so caller context logging fires

[PierreBrisorgueil]

Summary

• What changed: lib/helpers/mailer/index.js#sendMail and modules/audit/services/audit.service.js#log each wrapped their failing call in a local try/catch, logged one generic line, and resolved null instead of rejecting. Every caller's own context-rich .catch() (action/userId/orgId/targetType) never ran on a real outage — dead code hidden behind a swallowed rejection. Both helpers now propagate the underlying rejection; audit.middleware.js's .catch() is enriched with action/userId/organizationId/targetType/targetId so a write failure now logs full request context, not just message+stack. invitations.service.js#resend already documented "a transport failure surfaces as an error" but the swallow silently defeated that — propagation fixes it to match its own doc comment. On top of the propagation, resendVerification (auth) and the invitations resend endpoint now return a stable generic client message on a mail-transport failure instead of the raw provider error string — the real error is still logged server-side with context.
• Why: the "mail/audit failure never breaks the main flow" invariant was living inside the helpers via a silent swallow-and-return-null, which made every caller's existing .catch() dead code. Propagating moves that invariant to the call sites, which already carry (or, for the two resend endpoints, now carry) the right catch/logging. Propagating also surfaced a pre-existing leak: errors.getMessage(err) on those two endpoints relayed the raw SMTP/Resend provider error straight to the client (flagged by the pre-push critical-review gate) — fixed by giving those two catches a generic client message while still logging the real error server-side.
• Related issues: Closes 🔧 Propagate mail and audit write failures to callers #3966

Scope

• Module(s) impacted: lib/helpers/mailer, modules/audit (service + middleware), modules/auth/controllers, modules/invitations/controllers
• Cross-module impact: yes — every caller of mails.sendMail() and AuditService.log() now sees a rejecting promise instead of null. Audited: auth signup/reset, billing.email.js, invitations service (fire-and-forget create() path), organizations.membership.service.js (×4 sites), users email-change — all already carry their own context .catch(), so behavior is unaffected beyond that catch now actually running. resendVerification and invitations.resend were the two awaited (non-fire-and-forget) call sites without a local .catch() — hardened directly in this PR to log server-side and respond generically instead of relaying the raw error.
• Risk level: low — the "never break the main flow" invariant is preserved at every existing fire-and-forget call site; the two awaited call sites get new explicit handling instead of falling through to the old swallow-and-null path.

Validation

• npm run lint
• npm test (unit — 2189/2189 green, including new coverage for both hardened catches)
• Manual checks done (N/A — no user-facing behavior change beyond error propagation/messaging)

Tests assert: a provider/repo rejection reaches the caller's context .catch() (mailer + audit unit tests), the main flow never crashes on a mail/audit failure, and — new in this PR — the client response for a mail-transport failure on resendVerification/invitations.resend does not contain the raw provider error string while the server-side context log still fires.

Guardrails check

• No secrets or credentials introduced (.env*, secrets/**, keys, tokens)
• No risky rename/move of core stack paths
• Changes remain merge-friendly for downstream projects
• Tests added or updated when behavior changed

Notes for reviewers

• Security considerations: closes a low-severity info-leak — resendVerification and invitations.resend previously relayed the raw SMTP/Resend provider error string to the client via errors.getMessage(err). Both now log the real error server-side with context (userId / invitationId) and respond with a stable generic message ("Failed to send the email, please try again."). invitations.resend still threads deliberate AppError statuses (409 conflict, 404 not found, 422 mailer-not-configured) through unchanged — only the untagged transport rejection (no .status) gets the generic treatment.
• Mergeability considerations: resendVerification/invitations.resend now return 422 instead of the old misleading 400/200 on some previously-swallowed failure paths — intentional, more-correct status, not a regression.
• Follow-up tasks (optional): none

https://claude.ai/code/session_01WfNC8bt1TgL4AsiYgCEGup

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📥 Commits

Reviewing files that changed from the base of the PR and between b9f4951 and 782df4e.

📒 Files selected for processing (12)

• ERRORS.md
• lib/helpers/mailer/index.js
• lib/helpers/mailer/tests/mailer.unit.tests.js
• modules/audit/middlewares/audit.middleware.js
• modules/audit/services/audit.service.js
• modules/audit/tests/audit.middleware.unit.tests.js
• modules/audit/tests/audit.service.unit.tests.js
• modules/auth/controllers/auth.controller.js
• modules/auth/tests/auth.silent.catch.unit.tests.js
• modules/invitations/controllers/invitations.controller.js
• modules/invitations/tests/invitations.controller.unit.tests.js
• modules/invitations/tests/invitations.service.unit.tests.js

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• Create PR with unit tests
• Commit unit tests in branch fix/3966-propagate-mail-audit-failures

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 93.13%. Comparing base (ac772a4) to head (782df4e).
⚠️ Report is 2 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #3973      +/-   ##
==========================================
+ Coverage   93.06%   93.13%   +0.07%     
==========================================
  Files         170      170              
  Lines        5595     5596       +1     
  Branches     1802     1803       +1     
==========================================
+ Hits         5207     5212       +5     
+ Misses        313      309       -4     
  Partials       75       75              

Flag	Coverage Δ
integration	61.25% <50.00%> (-0.02%)	⬇️
unit	75.01% <100.00%> (+0.16%)	⬆️

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[PierreBrisorgueil]

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