- dav_router: PUT now looks up the event within the authenticated calendar only
(local_events.uid is globally unique), so a CalDAV client can no longer
overwrite another user's/calendar's event; a cross-calendar UID clash returns
409 instead of a 500 from the UNIQUE constraint.
- ical_router: _fetch_ics validates the URL (http/https only), resolves the host
and rejects private/loopback/link-local/reserved targets, follows redirects
manually re-validating each hop, and caps the response size — closing an
authenticated SSRF into internal services / cloud metadata.
- profile_router: GET /profile/avatar/{user_id} now requires authentication.
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
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