Invalid compound IDs lead to 400, should be 404

[lsmith77]

Description and expected behavior In case of using a compound ID on a model, a 400 error is returned when the supplied ID is missing chunks for any column.

ie. if the correct URL for a resource is /user/a_b on a constraint with 2 columns, when /user/a is called it leads to a 400 due to an error thrown from prisma.findUnique() receiving undefined in the where filter.

Screenshots

Environment (please complete the following information):

• ZenStack version: 2.17.2
• Prisma version: 6.10.0
• Database type: MariaDB

Additional context Issue was initially discovered in https://github.com/zenstackhq/zenstack/pull/2188

Some tentative approaches for fixes https://github.com/zenstackhq/zenstack/pull/2188#issuecomment-3163705895