Rails 8.1.3 does not recognize pgvector extension vector columns on PostgreSQL 18

Steps to reproduce

PostgreSQL 18.4 with pgvector extension 0.8.2

Migration:

class EnableVector < ActiveRecord::Migration[8.1]
  def change
    enable_extension "vector"

    execute <<~SQL
      CREATE TABLE items (
        id bigserial PRIMARY KEY,
        embedding vector(1536)
      )
    SQL
  end
end

Model:

class Item < ApplicationRecord
  self.table_name = "items"
end

Console:

Item.columns_hash["embedding"]

Actual behavior

Rails logs:

unknown OID XXXXX: failed to recognize type of 'embedding'

Column metadata shows:

@sql_type = "vector(1536)"
@type = nil

Expected behavior

Rails should recognize the column as a vector type and map it using ActiveRecord::ConnectionAdapters::PostgreSQL::OID::Vector.

Additional information

The vector type exists:

SELECT oid, typname, typelem, typtype
FROM pg_type
WHERE typname = 'vector';

Result:

typname = vector
typelem = 0
typtype = b

Rails includes:

ActiveRecord::ConnectionAdapters::PostgreSQL::OID::Vector

but the OID is not registered.

System configuration

Rails version: Rails 8.1.3

Ruby version: Ruby 4.0.5