ENG-3301: Refactor messaging dispatchers into provider classes (Story 1)

[JadeCara]

Ticket ENG-3301

Description Of Changes

Refactors the function-based dispatcher pattern in message_dispatch_service.py (~315 lines removed) into provider classes behind a two-level ABC hierarchy. This is PR 1 of 3 for ENG-3301 — it covers the structural refactor only (Story 1). Threading headers (Story 2) and correspondence scaffolding (Story 3) follow in separate PRs.

What changed:

• New ABC hierarchy: BaseMessageProviderService → BaseEmailProviderService / BaseSMSProviderService
• 5 provider classes replace the old _*_dispatcher functions: MailgunService, TwilioEmailService, AwsSesService, MailchimpTransactionalService, TwilioSmsService
• PROVIDER_MAP routes MessagingServiceType → provider class
• dispatch_message() signature is unchanged — all callers (fides + fidesplus) are unaffected

Intentional behavioral improvement:

• SES validate_email_and_domain_status() moved from per-send to config-time (advisory warning in update_config_secrets). SES itself rejects sends from unverified identities (MessageRejected), making the per-send check redundant. See plan Decision Port CI from GitLab CI to GitHub Actions #11 for rationale.

Test improvements:

• SES tests rewritten with moto[ses] instead of unittest.mock patches — exercises real boto3 client construction through moto
• Added moto[ses] to dev dependencies (moto[s3] → moto[s3,ses])

Reference: Based on patterns from Eli Rosselli's LJ-352-improvements branch (~Feb 2025, never merged), with divergences documented in the technical plan.

Code Changes

• New: src/fides/api/service/messaging/messaging_providers/ package — ABC base + 5 provider classes
• Modified: message_dispatch_service.py — replaced dispatcher functions with PROVIDER_MAP + _resolve_provider_map(), deleted ~315 lines
• Modified: messaging_endpoints.py — wired advisory SES validation into update_config_secrets()
• Deleted: src/fides/service/messaging/aws_ses_service.py — replaced by new AwsSesService provider
• Modified: pyproject.toml — moto[s3] → moto[s3,ses]
• Updated: 8 test files — mock paths updated from old _*_dispatcher functions to new provider classes

Steps to Confirm

1. All existing messaging tests pass unchanged (104 tests in tests/ops/service/messaging/ + tests/service/messaging/)
2. Integration test files (test_integration_dynamic_erasure_email.py, test_integration_attentive.py, test_integration_generic_email.py) collect without import errors
3. dispatch_message() signature unchanged — verify no fidesplus import breakage
4. SES config-time validation: saving SES config secrets logs a warning if identity not verified (advisory, non-blocking)

Pre-Merge Checklist

• Issue requirements met
• All CI pipelines succeeded
• CHANGELOG.md updated
  • Add a db-migration This indicates that a change includes a database migration label to the entry if your change includes a DB migration
  • Add a high-risk This issue suggests changes that have a high-probability of breaking existing code label to the entry if your change includes a high-risk change (i.e. potential for performance impact or unexpected regression) that should be flagged
  • Updates unreleased work already in Changelog, no new entry necessary
• UX feedback:
  • All UX related changes have been reviewed by a designer
  • No UX review needed
• Followup issues:
  • Followup issues created
  • No followup issues
• Database migrations:
  • Ensure that your downrev is up to date with the latest revision on main
  • Ensure that your downgrade() migration is correct and works
    • If a downgrade migration is not possible for this change, please call this out in the PR description!
  • No migrations
• Documentation:
  • Documentation complete, PR opened in fidesdocs
  • Documentation issue created in fidesdocs
  • If there are any new client scopes created as part of the pull request, remember to update public-facing documentation that references our scope registry
  • No documentation updates required

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2 Skipped Deployments

Project	Deployment	Actions	Updated (UTC)
fides-plus-nightly	Ignored	Preview	Apr 16, 2026 7:02pm
fides-privacy-center	Ignored		Apr 16, 2026 7:02pm

[github-actions]

Dependency Review

✅ No vulnerabilities found.

Snapshot Warnings

⚠️: No snapshots were found for the head SHA 0a01ec0.

Ensure that dependencies are being submitted on PR branches and consider enabling retry-on-snapshot-warnings. See the documentation for more information and troubleshooting advice.

Scanned Files

None

[codecov]

Codecov Report

❌ Patch coverage is 74.79339% with 61 lines in your changes missing coverage. Please review.
✅ Project coverage is 84.13%. Comparing base (c6fe17d) to head (0a01ec0).
⚠️ Report is 8 commits behind head on main.

Files with missing lines	Patch %	Lines
...saging/messaging_providers/twilio_email_service.py	64.00%	18 Missing ⚠️
...aging_providers/mailchimp_transactional_service.py	42.30%	15 Missing ⚠️
...e/messaging/messaging_providers/mailgun_service.py	77.14%	6 Missing and 2 partials ⚠️
.../api/service/messaging/message_dispatch_service.py	68.18%	3 Missing and 4 partials ⚠️
...essaging/messaging_providers/twilio_sms_service.py	81.25%	4 Missing and 2 partials ⚠️
src/fides/api/v1/endpoints/messaging_endpoints.py	14.28%	5 Missing and 1 partial ⚠️
...e/messaging/messaging_providers/aws_ses_service.py	98.11%	1 Missing ⚠️

❌ Your patch check has failed because the patch coverage (74.79%) is below the target coverage (100.00%). You can increase the patch coverage or adjust the target coverage.
❌ Your project check has failed because the head coverage (84.13%) is below the target coverage (85.00%). You can increase the head coverage or adjust the target coverage.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #7947      +/-   ##
==========================================
- Coverage   85.06%   84.13%   -0.94%     
==========================================
  Files         629      634       +5     
  Lines       40860    41045     +185     
  Branches     4748     4768      +20     
==========================================
- Hits        34759    34533     -226     
- Misses       5029     5365     +336     
- Partials     1072     1147      +75     

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[JadeCara]

Superseded by #8118 (4 providers) and #8120 (AWS SES). Split into two smaller PRs.