format_version: "0.1"
id: g_two_hand_fb
name: "two-hand control as a function block"
domain: manufacturing
language: LD-graphical
source:
  origin: authored
  reference: "The ISO 13851 Type II logic of g_two_hand moved into a reusable function block, the shape certified safety libraries ship it in"
  license: CC-BY-4.0
properties_file: props.yaml
safety_intent: "The ram must descend only while both hand actuators are held; releasing either one must stop the stroke."
validation_status: candidate
syntax_pair_of: g_two_hand
variants:
  - file: program.xml
    expected_verdict: true
    ground_truth:
      method: expert
      witness: "Ground truth is the ladder twin g_two_hand, which both builds verify. Here both builds fail the ingestion gate: Stroke is never driven, because the frontend does not bind the block's actual parameters."
  - file: type_i.xml
    expected_verdict: true
    ground_truth:
      method: fault-injection
      base_variant: program.xml
      seeded_defect: "The arming latch is dropped from the block body, leaving the Type I conjunction, exactly as in g_two_hand/type_i.xml."
      witness: "Expected SAFE by construction and confirmed on the ladder twin. Both builds report VIOLATION here, because a binary boolean in a function-block body is reduced to its first operand."
features: [function_block, multi_pou, latch]
difficulty: medium
tags: [safety-function, frontend-gap, syntax-pair]