Address the two Security findings from PR review:
- webhook_receiver: encode Authorization header and expected bearer to
utf-8 bytes before hmac.compare_digest. Conventional form; doesn't
rely on Python's implicit ASCII encoding.
- webhook_routes: html.escape user-influenced and exception-derived
strings before interpolating into HTMLResponse content. Covers the
preset_id path param echoed in the "Unknown preset" branch and the
str(e) text rendered on handler exceptions.
Adds regression tests verifying compare_digest is invoked on bytes and
that <script> payloads (in preset_id and exception messages) are
emitted as escaped entities, not active markup.
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
