Fix value.Contains(enumMember) execution failure on enum document members

[jeremydmiller]

Problem

A user-reported execution-time bug: with a CLR enum document member and an in/Contains-shaped LINQ predicate (the form HotChocolate's [UseFiltering] in operator emits), the parsed query throws at execution with:

System.InvalidCastException : Writing values of 'YourEnum[]' is not supported
for parameters having NpgsqlDbType '-2147483639'.

Distinct from the parse-time #4599 / #4600 / #4601 family already shipped in 8.37.2 — this is downstream, at parameter-bind time.

Root cause

EnumerableContains.Parse builds:

return new IsOneOfFilter(collectionMember, new CommandParameter(constant.Value));

When the document member is an enum, constant.Value is a CLR EnumType[] (or List<EnumType>). Npgsql has no parameter mapping for an arbitrary enum array unless the enum is a registered Postgres enum type, so it fails at the parameter-bind step with NpgsqlDbType '-2147483639' (= Array | <ordinal 9>).

The parallel LinqExtensions.IsOneOf path already handled this exact case via EnumIsOneOfWhereFragment (IsOneOf.cs:36), which projects the array into string[] (for EnumStorage.AsString) or int[] (for AsInteger) with the right NpgsqlDbType. The Contains shape just didn't route through it.

The bug was actually broader than the user reported: both AsString and AsInteger enum-storage modes were affected on the Contains path — the AsString user reported it because that's the more common config.

Fix

Route the enum case in EnumerableContains.Parse through EnumIsOneOfWhereFragment, mirroring IsOneOf.cs:36. A small List<T>→T[] coercion handles non-array constant collections, since EnumIsOneOfWhereFragment requires a System.Array.

Tests

New Bug_enum_asstring_array_contains covers:

• Scalar == canary on AsString — must keep working (already worked, but pinned).
• Array Contains on AsString — headline regression.
• List<> Contains on AsString — the non-array constant shape.
• Single-element collection — degenerate IN.
• Empty collection — must not throw; matches zero rows.
• Array Contains on AsInteger — the broader half of the bug; pinned as a canary going forward.

Pre-fix: all 5 Contains tests fail with the reported Writing values of … is not supported. Post-fix: all 6 pass.

Regression sweeps: full LinqTests (1269 passed) + full ValueTypeTests (339 passed) — strongly-typed IDs share the EnumerableContains parse path so worth pinning.

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