Feature: Graph Tool Node Execution (Issue #75)
  As a developer
  I want `type: tool` graph nodes to dispatch to ToolAgent via the `tool:` YAML key
  So that graph-driven tool invocation actually calls real tool handlers

  Scenario: NodeConfig accepts tool and static_config fields
    Given a fresh graph tool node test context (gTN)
    When I create a NodeConfig with tool and static_config fields (gTN)
    Then the NodeConfig should have tool set and static_config preserved (gTN)

  Scenario: tool: key parsed from raw node config in runtime_dispatch
    Given a fresh graph tool node test context (gTN)
    When I parse a node definition with a tool: key through execute_graph (gTN)
    Then the resulting NodeConfig should have tool set and static_config populated (gTN)

  Scenario: ToolAgent.invoke() calls _execute_tool with correct args
    Given a fresh graph tool node test context (gTN)
    When I call ToolAgent.invoke() with a known tool name (gTN)
    Then the tool should execute and return the expected result (gTN)

  Scenario: Node._execute_tool threads previous-node output as input
    Given a fresh graph tool node test context (gTN)
    When I execute a tool node with state containing previous messages (gTN)
    Then the tool should receive the previous output threaded as input (gTN)

  Scenario: Node._execute_tool merges static_config with dynamic input
    Given a fresh graph tool node test context (gTN)
    When I execute a tool node with static_config and previous output (gTN)
    Then the tool args should contain both static config and threaded input (gTN)

  Scenario: Node._execute_tool returns structured error when no agent found
    Given a fresh graph tool node test context (gTN)
    When I execute a tool node with no matching agent (gTN)
    Then it should return metadata with tool_error (gTN)

  Scenario: Node._execute_tool returns empty dict when tool is None
    Given a fresh graph tool node test context (gTN)
    When I execute a tool node without a tool: field (gTN)
    Then it should return an empty dict (gTN)

  Scenario: Node.execute dispatcher passes state to _execute_tool
    Given a fresh graph tool node test context (gTN)
    When I exercise execute() with type TOOL and state (gTN)
    Then the result should include the tool execution response (gTN)

  Scenario: Default behaviour preserved for type:tool nodes with tools: list and no tool: field
    Given a fresh graph tool node test context (gTN)
    When I execute a tool node with tools: list but no tool: field (gTN)
    Then it should return metadata with tool_results (backward compatible) (gTN)

  Scenario: Auto-created ToolAgent handles tool dispatch via invoke
    Given a fresh graph tool node test context (gTN)
    When I exercise a complete tool node pipeline with auto-created agent (gTN)
    Then the tool should execute and return correct result (gTN)

  Scenario: static_config blocks are preserved for tool nodes in YAML nodes processing
    Given a fresh graph tool node test context (gTN)
    When I create NodeConfig via create_pure_langgraph with config block (gTN)
    Then the static_config should match the original config block (gTN)