EQL v3 JSON on Supabase: encrypted containment + JSONPath selector querying

[coderdan]

Follow-up to #623 (which added the JSONPath selector-with-constraint to the Drizzle v3 integration).

Problem

The Supabase v3 adapter has no encrypted-JSON querying at all — not even the #621 containment (that lives only in Drizzle). searchableJson / query_jsonb / ste_vec / selector have zero references in packages/stack-supabase/src/. Encrypted eql_v3_json columns round-trip through select/insert, but they are non-queryable on this surface, and the typed key sets actively exclude them (a JSON column resolves to never in QueryTypesForColumn).

So Supabase needs BOTH:

1. Encrypted-JSON containment (@>), the Drizzle feat(stack): EQL v3 JSON support — types.Json + containment #621 equivalent.
2. JSONPath selector-with-constraint (col->'path' <op> value), the EQL v3 JSON: implement JSONPath selector-with-constraint querying (->, ->>) #623 equivalent.

The hard part: PostgREST can't cast a filter value

The Drizzle path works because it emits raw SQL with the casts the overloads require (::eql_v3.query_jsonb for containment, ::public.eql_v3_jsonb_entry for the selector comparison). PostgREST has no syntax to cast a filter value, and an uncast literal is ambiguous across the @> / comparison overloads (42725 "operator is not unique"). This is the same wall the scalar v3 filters hit — they escape it by sending the full storage envelope to a no-cast overload, but a JSON query needle can't be a full storage envelope.

Required investigation (do this first)

A live-PostgREST probe to find a filter form that reaches an overload needing no value cast — mirroring how ordering already works (order=col->op.asc needs no operand/cast; see query-builder-v3.ts:282-320). If no such form exists for the encrypted-JSON overloads, this needs an EQL-bundle change (a no-cast-friendly overload) — coordinate with the EQL project.

Plumbing (once the wire form is settled)

• Core: add a searchableJson arm to QueryTypesForColumn (packages/stack/src/eql/v3/columns.ts:770) so JSON columns stop resolving to never.
• packages/stack-supabase/src/types.ts: a V3SearchableJsonKeys key set (sibling to V3EncryptedFreeTextKeys), remove JSON columns from NonQueryableV3Keys erasure, add a FilterOp member + builder method.
• packages/stack-supabase/src/query-builder-v3.ts: widen V3ColumnLike.getQueryCapabilities, add searchableJson arms to queryTypeForRawOp/queryTypeForOrOp/assertTermQueryable, and a new applier seam beside applyContainsFilter.
• Reference impl: packages/stack-drizzle/src/v3/operators.ts (containment containsJsonOp; selector selectorCompare) and sql-dialect.ts.
• Live tests in packages/stack-supabase/integration/wire.integration.test.ts (add an eql_v3_json fixture column).

Context

Split out of #623 during the Stack 1.0 push: the Drizzle selector was clean and unblocked, but the Supabase path needs genuine PostgREST design work that shouldn't gate the Drizzle capability for launch.