Function value_to_bson_for_query 

pub fn value_to_bson_for_query(
    schema: &ClassSchema,
    field: &str,
    value: &ParseValue,
) -> Result<Bson, ParseError>

Lower a value for use in a query filter on field.

Differs from the create path in one way that matters: a declared Pointer field stores "Class$id", so a query for a pointer has to compare against that string rather than against the __type envelope. Getting this wrong makes every pointer query silently return nothing.

A bare objectId string is prefixed too, and only the schema knows what to prefix it with. transformTopLevelAtom’s string case is if (field && field.type === 'Pointer') return ${field.targetClass}$${atom}`` (MongoTransform.js:600-603), so {"author": {"$in": ["abc123"]}} compares against "Post$abc123" upstream. Handling only the __type envelope left the raw-string form comparing against the unprefixed id, which matches no stored value: the query answers 200 with no results rather than erroring, so nothing indicates the constraint was meaningless. The class comes from the schema, not from the value, because a bare string carries none.