fix(webhooks): handle svix 2.0.0 Webhook.verify() returning None

[Sbussiso]

Root cause

The Weekly dependency refresh workflow (run #32700481827) runs uv lock --upgrade before the test gate. That resolved svix>=1.99.1 → svix 2.0.0, a breaking major release.

svix 2.0.0 changed Webhook.verify() to return None — it now only validates the signature; the parsed event dict is no longer returned (signature changed from -> dict to -> None). Both webhook handlers did event = wh.verify(payload, headers) then event.get("type"), so 39 tests crashed with:

AttributeError: 'NoneType' object has no attribute 'get'
app/api/webhooks.py:102: event_type = event.get("type")

Affected: all of test_resend_webhook.py, test_webhooks.py, and test_welcome_email.py (both the Clerk /api/webhooks/clerk and Resend /api/webhooks/resend routes).

Fix

Keep wh.verify() as the signature-validation call (it still raises WebhookVerificationError on a bad signature in both svix 1.x and 2.x), then parse the now-authentic payload with json.loads() ourselves. This is version-agnostic:

• svix 1.99.1 — verify() returns the dict; we overwrite it with the same dict (no-op).
• svix 2.0.0 — verify() returns None; we parse the verified bytes.

verify() succeeding is proof the payload is authentic, so decoding it ourselves is safe and equivalent to what the library used to do internally.

Verification

Reproduced the CI failure locally (installed svix 2.0.0 via uv lock --upgrade), then confirmed the fix:

• ✅ Full backend suite: 699 passed, 0 failed under svix 2.0.0 (includes all 39 previously-failing webhook tests)
• ✅ ruff check clean
• ✅ The 3 previously-failing test files pass standalone: 43 passed

This also lets the weekly refresh PR go green again — without this fix, every weekly refresh that pulls svix 2.0.0 will stay red.

CI run

https://github.com/SourceBox-LLC/Sentinel-Command/actions/runs/32700481827