Feature: LangGraph nodes coverage boost
  Scenarios targeting specific uncovered lines in nodes.py

  # Line 130 – execute() else branch when NodeType is unrecognised
  Scenario: Unknown node type falls through to empty result
    Given a node whose type is patched to an unrecognised value
    When I execute the unknown-type node
    Then the result should contain current_node and nothing else

  # Line 176 – ToolAgent branch with empty current_message falls back to last message
  Scenario: ToolAgent with empty current_message falls back to last message content
    Given a ToolAgent node with an empty current_message and messages in state
    When I execute the ToolAgent fallback node
    Then the ToolAgent should receive the last message content as input

  # Line 270 – _execute_function raises when function is not callable
  Scenario: Function node raises when the registered object is not callable
    Given a function node whose registered object is not callable
    When I execute the non-callable function node
    Then the result should report a not-callable error

  # Lines 319, 321-322 – message router rules with null target / null condition
  Scenario: Message router skips rules with null target
    Given a message router with a rule that has no target
    When I execute the null-target router
    Then the router should return routed_to as None

  Scenario: Message router matches unconditional rule
    Given a message router with an unconditional rule targeting "default_dest"
    When I execute the unconditional router
    Then the router should route to "default_dest"

  Scenario: Message router skips null-target then matches unconditional rule
    Given a message router with a null-target rule followed by an unconditional rule to "fallback"
    When I execute the mixed-rules router
    Then the router should route to "fallback"

  # Line 337 – evaluate_edge_condition returns True for edge without condition
  Scenario: Edge without condition evaluates to true
    Given an edge with no condition
    When I evaluate the unconditioned edge
    Then the edge evaluation should return true