docs: AV13–AV15, and two lessons from how they were found

AV13 the mail gate, AV14 the MHP audience and the hub's own identity, AV15
the shape check on the unauthenticated blocklist endpoints. §13.5b also
records the auto-block threshold as an open decision rather than a defect.

Two lessons, both about tests.

A fixture narrower than production tests the fixture — and when it writes down
*why* it has to be narrow, that is a bug report nobody filed. Two test helpers
described the federation defects accurately, in comments, while routing
around them.

And a global's state is not a given, in a test least of all. One assertion —
that a refusal never logs the address — took three attempts, each passing
alone and failing in the full run, for three different reasons: caplog saw
nothing because the app configures logging, then a handler saw nothing
because an earlier test raised the logger's level, then because `disabled`
was left True.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01T4YmK41VsEURWFdop4EEeT

0 files changed, 0 insertions, 0 deletions