The SameSite=None change left clear_pkce_cookie() deleting every name
variant with `SameSite=None; Secure` unconditionally. Over loopback
HTTP the setter emits a bare-name cookie with `SameSite=Lax` and no
`Secure` — a Secure deletion on a plain-HTTP origin can be ignored by
the browser, leaving a stale PKCE cookie behind after callback/logout.
Thread use_https from the request into clear_pkce_cookie() and derive
both the set and clear attribute shapes from one helper (_pkce_attrs)
so they cannot drift apart again. The __Host-/__Secure- variants keep
`Secure; SameSite=None` regardless of origin — those names require
Secure to be valid at all and only ever exist on HTTPS origins.
Adds contract tests pinning the full Set-Cookie shape on both origins
for set and clear, and updates the dashboard cookie documentation
(which still claimed all cookies are SameSite=Lax).
Ben Barclay
5e57bf19a2