An abstract base shares one provider's declarations

[czpython]

One provider often backs several services — Google backs Gmail and Google Calendar, and each keeps its own card, its own key, and its own blast radius. Until now every one of them re-declared the provider's OAuth quirks: both endpoints, extra_authorize_params = {"access_type": "offline", "prompt": "consent"}, the identity endpoint and its scopes, and the same two-field Settings.

Service now accepts abstract = True. An abstract base never registers and skips validation; each subclass inherits everything the base declares — Settings included, since the validator now reads Settings through inheritance — and registers itself:

class GoogleOauth(Service):
    abstract = True
    authorization_endpoint = "https://accounts.google.com/o/oauth2/v2/auth"
    token_endpoint = "https://oauth2.googleapis.com/token"
    extra_authorize_params = {"access_type": "offline", "prompt": "consent"}
    identity_endpoint = "https://openidconnect.googleapis.com/v1/userinfo"
    identity_scopes = ("openid", "email")

    class Settings(BaseModel):
        client_id: str = Field(title="Client ID")
        client_secret: SecretStr = Field(title="Client secret")


class Gmail(GoogleOauth):
    name = "gmail"
    title = "Gmail"

The contract stays loud: abstract must be set in the class's own body (it never leaks to children), a class that sets both abstract and name raises at definition, a concrete subclass that forgets name still raises, and a base declaring only one OAuth endpoint fails on its first concrete subclass — the endpoint checks read through the MRO. Typing improves too: the base's declarations are checked against Service's ClassVar annotations, so a wrong-shaped quirk fails pyright at the definition site instead of surfacing at runtime.