fix: resolve domain types to their base type serializer/parser

[san7iya]

Fixes #592

Postgres domain types (CREATE DOMAIN x AS text[]) aren't tagged with typcategory = 'A', so fetchArrayTypes() never registered a serializer/parser for them — inserting into a domain-typed array column failed with malformed array literal.

This adds a lookup for domain types (typtype = 'd'), resolving each domain's OID back to its base type (typbasetype) and reusing whichever serializer/parser is already registered for that base type.

Both lookups are combined into a single round-trip (multi-statement query, same pattern already used in fetchState()) rather than two separate queries. An earlier version of this fix used two sequential awaited queries, which introduced a race condition: needsTypes flips to false after the first round-trip completes, which lets the connection execute the next queued query before a second query would have finished populating the serializer map. Bundling both into one round-trip avoids that.

Verified locally against PostgreSQL 18 with both a domain-wrapped array column and a plain array column, confirming correct storage and no regression in the plain-array path. Added a test following the existing array-test conventions in tests/index.js; wasn't able to run the full local suite due to its Linux-oriented bootstrap script (creates test users via bare psql/createdb calls), but the new test's logic is verified in isolation and CI should cover the rest.

[Copilot]

Pull request overview

Fixes array serialization for Postgres domain types that wrap arrays (e.g. CREATE DOMAIN x AS text[]) by resolving each domain OID to its base type OID and reusing the existing serializer/parser for that base type, preventing malformed array literal errors on inserts.

Changes:

• Extend fetchArrayTypes() to also fetch domain types (typtype='d') in the same round-trip and register domain OIDs to use their base type serializer/parser.
• Add addDomainType() to map domain OIDs to base type handlers.
• Add a regression test covering a domain-wrapped array column insert/return round-trip.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 1 comment.

File	Description
src/connection.js	Adds domain type resolution/mapping so domain OIDs reuse base serializers/parsers (and combines lookups into one round-trip).
tests/index.js	Adds regression coverage for inserting/returning an array via a domain-wrapped array column.

Suppressed comments (1)

src/connection.js:797

• addDomainType unconditionally overwrites parsers/serializers for the domain OID when a base mapping exists. This can clobber user-provided type handlers (mergeUserTypes allows custom parsers/serializers), which is an API-breaking behavior change. Only fill in missing handlers for the domain OID.

  function addDomainType(oid, basetype) {
    if (options.parsers[basetype]) options.parsers[oid] = options.parsers[basetype]
    if (options.serializers[basetype]) options.serializers[oid] = options.serializers[basetype]
  }

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