Feature: PureGraph coverage
  As a developer
  I want to cover uncovered lines in PureGraph
  So that code coverage improves for pure_graph.py

  Scenario: Topological order keeps start and end boundaries
    Given a pure graph with nodes "alpha" and "beta"
    When I list its topological order
    Then the order should be start alpha beta end

  Scenario: Execute applies registered node functions sequentially
    Given a pure graph with function nodes "double" and "increment"
    And registered functions that double then increment
    When I execute the pure graph starting with 1
    Then the final result should be 3
    And the functions should run in declaration order

  Scenario: Execute skips unregistered functions
    Given a pure graph with a missing function node
    When I execute the pure graph starting with 5
    Then the result should remain 5

  Scenario: Nodes without functions do not change value
    Given a pure graph with non-functional nodes "alpha" and "beta"
    When I execute the pure graph starting with 7
    Then the result should remain 7