`OpenAPIParameter.schema.format` incompatible with `exactOptionalPropertyTypes`

[ebramanti]

When exactOptionalPropertyTypes: true is enabled (e.g. via @tsconfig/strictest), better-call@1.1.8's OpenAPIParameter type causes type errors for plugins that emit format?: undefined in their OpenAPI parameter metadata.

The issue is in dist/openapi.d.mts (and .d.cts):

schema?: {
  type: OpenAPISchemaType;
  format?: string;  // should be `format?: string | undefined`
};

Under exactOptionalPropertyTypes, format?: string means the property can be absent but if present must be string — it cannot be undefined. Plugins like @better-auth/oauth-provider generate endpoint types where format is explicitly undefined, producing:

Type 'undefined' is not assignable to type 'string'

PR better-auth/better-auth#6502 fixed this class of issue for the OIDC and JWT plugins, but better-call's OpenAPIParameter type still has the same problem, which surfaces through oauth-provider's oauth2Authorize endpoint.

Fix: Change format?: string to format?: string | undefined in the OpenAPIParameter interface.

[eabnelson]

+1 ran into this too. Would have saved us a lot of time