Feature: Invariant data model and database schema
  As a developer
  I want an Invariant SQLAlchemy model with a corresponding database schema
  So that invariant rules can be persisted and queried efficiently

  Background:
    Given a fresh in-memory invariant database

  Scenario: Create an Invariant with all required fields
    Given a new Invariant with description "All plans must have a goal"
    When I persist the Invariant
    Then I can retrieve the Invariant by its ID
    And the persisted Invariant description should be "All plans must have a goal"

  Scenario: is_active defaults to True
    Given a new Invariant with description "Default active invariant"
    When I persist the Invariant
    Then I can retrieve the Invariant by its ID
    And the persisted Invariant is_active should be True

  Scenario: created_at is auto-populated on insert
    Given a new Invariant with description "Timestamped invariant"
    When I persist the Invariant
    Then I can retrieve the Invariant by its ID
    And the persisted Invariant created_at should not be empty

  Scenario: id is a UUID string
    Given a new Invariant with description "UUID invariant"
    When I persist the Invariant
    Then I can retrieve the Invariant by its ID
    And the persisted Invariant id should be a valid UUID

  Scenario: description is required and cannot be empty
    Given a new Invariant with an empty description
    When I try to persist the Invariant
    Then a ValueError should be raised for empty description

  Scenario: Query active invariants
    Given 3 active Invariants and 2 inactive Invariants
    When I query Invariants filtered by is_active True
    Then I should get 3 Invariants

  Scenario: Query inactive invariants
    Given 3 active Invariants and 2 inactive Invariants
    When I query Invariants filtered by is_active False
    Then I should get 2 Invariants

  Scenario: Deactivate an Invariant
    Given a persisted active Invariant
    When I set is_active to False on the Invariant
    Then the Invariant is_active should be False

  Scenario: Migration upgrade creates invariants table
    Given a fresh in-memory invariant database
    Then the invariants table should exist

  Scenario: Migration creates index on is_active
    Given a fresh in-memory invariant database
    Then the invariants table should have an index on is_active