A cookie-carrying mutation without Origin and Referer (or with an
unparsable one) is now rejected with 403 csrf_origin_mismatch instead
of passing unchecked. The exception for non-browser clients stays
structural: PAT/bearer requests carry no session cookie and never reach
the check, and a request that does carry the cookie is always checked.
The test harness injects the matching Origin (supertest simulates a
browser page of this instance) with an explicit suppression header for
the negative cases; the Playwright fixture contexts send the header on
their manual seeding calls; release-qa.sh pins APP_BASE_URL and sends
the matching Origin. Dedicated spec covers: missing headers 403,
mismatch 403, unparsable 403, match passes, GETs untouched, PAT
mutation without headers passes, cookie+bearer still checked.
Refs #189
Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_0168Ph5uBmHm8X28CSVpbpnJ
