Opus advisor flagged that PR #2171's credential prefilter only listed
specific DB scheme prefixes and form keys, letting OAuth callback URLs,
URL userinfo, signed-URL query params bypass the hard agent redactor.
Adding the generic '://' marker restores the WebUI-as-hard-safety-boundary
contract. Plain URLs without sensitive substrings still pass through
unchanged because the redactor itself only mutates sensitive substrings.
Regression-pinned with 5 new parametric cases in test_security_redaction.py
plus 1 negative-case companion. Verified test FAILS without the fix and
PASSES with it.