The persistent login cookie's max_age hardcoded 60 * 60 * 24 * 7, an
independent copy of the session token lifetime that core/auth.py already
defines once as TOKEN_TTL (and reports to the frontend via /api/auth/policy
as session_days). If TOKEN_TTL changes, the cookie silently drifts: the
browser keeps a cookie for a token whose lifetime no longer matches.
Import TOKEN_TTL and use it for the cookie max_age so the session lifetime
has a single source of truth. No behaviour change at the current value.
Fixes#4471
Added PASSWORD_MIN_LENGTH and RESERVED_USERNAMES to src/constants.py as the
single source of truth. Previously PASSWORD_MIN_LENGTH was hardcoded as 8 in
four route handlers and all three JS validation paths; RESERVED_USERNAMES was
an inline frozenset duplicated in core/auth.py, routes/assistant_routes.py,
routes/research_routes.py, and src/task_scheduler.py.
Added GET /api/auth/policy (unauthenticated) so the frontend reads the real
values from the server instead of hardcoding them in JS.
Added missing empty-username guard to /setup and admin POST /users. Both
returned a misleading 500/409 on whitespace-only input. /signup already had the
check; this makes all three consistent.
Karl Jussila