AddColumn with inline checkConstraint on an existing table double-applies the constraint (42710)

[MelbourneDeveloper]

What happened

DataProviderMigrate (postgres, additive phase) over a declarative schema where an existing table gains one new column that carries a checkConstraint:

      - name: workspace_size
        type: Text
        checkConstraint: "workspace_size IS NULL OR workspace_size IN ('small','medium','large')"

Plan and outcome:

Phase: all — applying 2 of 2 operation(s):
  AddColumnOperation
  AddCheckConstraintOperation
Error: migration apply failed: 42710: constraint "agent_configs_workspace_size_chk" for relation "agent_configs" already exists

The whole apply rolls back, so the column never lands: information_schema.columns and pg_constraint both show nothing afterwards, and every re-run fails the same way.

Diagnosis

AddColumnOperation already emits the column-level CHECK (named <table>_<column>_chk), and the planner also schedules a separate AddCheckConstraintOperation for the same declaration with the same name. On a fresh CREATE TABLE this does not happen, which is why the same YAML pattern works for columns declared at table-creation time.

Expected

One of:

• the planner emits only AddColumnOperation (with the inline check) when the column is new, or
• AddColumnOperation emits the bare column and leaves the check to AddCheckConstraintOperation.

Environment

• Postgres 17 (Supabase)
• Provider: postgres
• Consumer: Nimblesite/NimblesiteAgenticPlatform migrations/schema.yaml, table agent_configs