diff --git a/docs/evidence/phase4/2026-09-06-phase4g-challenges.md b/docs/evidence/phase4/2026-09-06-phase4g-challenges.md
new file mode 100644
index 0000000..b83a42e
--- /dev/null
+++ b/docs/evidence/phase4/2026-09-06-phase4g-challenges.md
@@ -0,0 +1,11 @@
+# Slice 4g: challenge fixtures and first exhibit visuals
+
+Implemented September 6, 2026. `tools/visual-challenge-fixtures.mjs` authors all fourteen PRD 130 challenge compositions and first visuals for Exhibits A–D. Generated `.xzbt` files are under `exhibits/visual-challenges` and `exhibits/exhibit-{a,b,c,d}.xzbt`.
+
+Each composition uses only existing generic primitives, systems, fields, behaviors, bindings and effects. No subject-specific renderer branch was added. The challenge suite validates every document, executes 120 logical ticks twice with different draw frequencies, verifies finite geometry and nonempty frame plans, compares final plans, and verifies cleanup. A nineteenth test checks deterministic standalone generation, embedded fixture identity and JavaScript syntax.
+
+The standalone `prototypes/phase4/XZBT-visual-acceptance.html` embeds production code and all eighteen fixtures. It provides fixture selection, pause/resume, seed restart, transient spawning, synthetic audio/state sliders and user observation export. Rebuild with `npm run build:visual-acceptance`.
+
+Exhibit D uses static text labels and state-driven geometry/layer presentation under the 0.1 contract. Live numeric string formatting was not added. The audio-reactive fixture uses the shared signal-binding surface; its review-page slider supplies an explicitly synthetic signal. Full A–D audio, cadence, scenario and final reference-suite obligations remain assigned to their later phases.
+
+The PRD 130 visual judgment is still a user-observed gate, and this artifact is not the 4h benchmark. No browser/display judgment or measured GC6 result is claimed by these tests.
diff --git a/exhibits/exhibit-a.xzbt b/exhibits/exhibit-a.xzbt
new file mode 100644
index 0000000..b4fb9d9
--- /dev/null
+++ b/exhibits/exhibit-a.xzbt
@@ -0,0 +1,110 @@
+{
+  "xzbt": "0.1",
+  "meta": {
+    "id": "exhibit-a",
+    "name": "Exhibit A — Procedural Machine",
+    "version": "0.1.0",
+    "description": "First visual composition; full reference exhibit acceptance remains Phase 9."
+  },
+  "runtime": {
+    "seed": 42
+  },
+  "visuals": {
+    "scene": {
+      "coordinateSpace": "virtual",
+      "width": 960,
+      "height": 540,
+      "background": "#101d25"
+    },
+    "systems": {
+      "wheel": {
+        "type": "graphic",
+        "content": {
+          "outer": {
+            "type": "ring",
+            "position": {
+              "x": 480,
+              "y": 270
+            },
+            "radius": 160,
+            "innerRadius": 158,
+            "style": {
+              "fill": "#72c4bd"
+            }
+          },
+          "inner": {
+            "type": "ring",
+            "position": {
+              "x": 480,
+              "y": 270
+            },
+            "radius": 125,
+            "innerRadius": 123,
+            "style": {
+              "fill": "#e1bd7c"
+            }
+          },
+          "hub": {
+            "type": "ring",
+            "position": {
+              "x": 480,
+              "y": 270
+            },
+            "radius": 38,
+            "innerRadius": 36,
+            "style": {
+              "fill": "#e1bd7c"
+            }
+          }
+        }
+      },
+      "spokes": {
+        "type": "repeater",
+        "count": 12,
+        "distribution": {
+          "type": "point",
+          "position": {
+            "x": 480,
+            "y": 270
+          }
+        },
+        "repeat": {
+          "type": "group",
+          "transform": {
+            "rotation": {
+              "op": "multiply",
+              "args": [
+                {
+                  "ref": "repeat.fraction"
+                },
+                330
+              ]
+            }
+          },
+          "behaviors": [
+            {
+              "type": "rotate",
+              "speed": 12
+            }
+          ],
+          "children": {
+            "bar": {
+              "type": "rectangle",
+              "position": {
+                "x": 40,
+                "y": -4
+              },
+              "size": {
+                "width": 85,
+                "height": 8
+              },
+              "style": {
+                "fill": "#e1bd7c"
+              }
+            }
+          }
+        }
+      }
+    }
+  }
+}
diff --git a/exhibits/exhibit-b.xzbt b/exhibits/exhibit-b.xzbt
new file mode 100644
index 0000000..6fc9330
--- /dev/null
+++ b/exhibits/exhibit-b.xzbt
@@ -0,0 +1,178 @@
+{
+  "xzbt": "0.1",
+  "meta": {
+    "id": "exhibit-b",
+    "name": "Exhibit B — Deep Abstract Field",
+    "version": "0.1.0",
+    "description": "First visual composition; full reference exhibit acceptance remains Phase 9."
+  },
+  "runtime": {
+    "seed": 42
+  },
+  "visuals": {
+    "scene": {
+      "coordinateSpace": "virtual",
+      "width": 960,
+      "height": 540,
+      "background": "#101d25"
+    },
+    "systems": {
+      "network": {
+        "type": "particles",
+        "count": 65,
+        "capacity": 96,
+        "distribution": {
+          "type": "rectangle",
+          "center": {
+            "x": 480,
+            "y": 270
+          },
+          "size": {
+            "width": 800,
+            "height": 410
+          }
+        },
+        "render": {
+          "type": "point",
+          "style": {
+            "fill": "#d8e9f5",
+            "pointSize": 4
+          }
+        },
+        "links": {
+          "rule": "nearest",
+          "count": 3,
+          "maxDistance": 180,
+          "maxLinks": 160,
+          "fadeWithDistance": true,
+          "style": {
+            "stroke": "#6899b7",
+            "strokeWidth": 1
+          }
+        },
+        "behaviors": [
+          {
+            "type": "noise-displace",
+            "amplitude": {
+              "x": 25,
+              "y": 25
+            },
+            "scale": 120,
+            "speed": 0.1
+          }
+        ]
+      },
+      "morph": {
+        "type": "graphic",
+        "content": {
+          "shape": {
+            "type": "spline",
+            "points": [
+              {
+                "x": 100,
+                "y": 250
+              },
+              {
+                "x": 195,
+                "y": 344.2081569929845
+              },
+              {
+                "x": 290,
+                "y": 225.72359530745103
+              },
+              {
+                "x": 385,
+                "y": 162.0476051788654
+              },
+              {
+                "x": 480,
+                "y": 296.94076835816776
+              },
+              {
+                "x": 575,
+                "y": 325.85627569923156
+              },
+              {
+                "x": 670,
+                "y": 183.51190467861346
+              },
+              {
+                "x": 765,
+                "y": 191.27697433748185
+              },
+              {
+                "x": 860,
+                "y": 331.6203724113671
+              }
+            ],
+            "style": {
+              "stroke": "#ecbf85",
+              "strokeWidth": 4
+            },
+            "behaviors": [
+              {
+                "type": "morph",
+                "to": "target",
+                "duration": "6s",
+                "loop": "ping-pong"
+              }
+            ]
+          },
+          "target": {
+            "type": "spline",
+            "points": [
+              {
+                "x": 100,
+                "y": 420
+              },
+              {
+                "x": 195,
+                "y": 363.24149524059965
+              },
+              {
+                "x": 290,
+                "y": 235.91968579603693
+              },
+              {
+                "x": 385,
+                "y": 134.38917869744083
+              },
+              {
+                "x": 480,
+                "y": 135.48623754987796
+              },
+              {
+                "x": 575,
+                "y": 238.38063008538305
+              },
+              {
+                "x": 670,
+                "y": 365.2039313913952
+              },
+              {
+                "x": 765,
+                "y": 419.97879545751226
+              },
+              {
+                "x": 860,
+                "y": 361.25269717983815
+              }
+            ],
+            "style": {
+              "stroke": "#82b7c7",
+              "strokeWidth": 2
+            },
+            "visible": false
+          }
+        }
+      }
+    },
+    "effects": [
+      {
+        "type": "bloom",
+        "radius": 5,
+        "intensity": 0.5
+      }
+    ]
+  }
+}
diff --git a/exhibits/exhibit-c.xzbt b/exhibits/exhibit-c.xzbt
new file mode 100644
index 0000000..8c0815e
--- /dev/null
+++ b/exhibits/exhibit-c.xzbt
@@ -0,0 +1,175 @@
+{
+  "xzbt": "0.1",
+  "meta": {
+    "id": "exhibit-c",
+    "name": "Exhibit C — Natural Environment",
+    "version": "0.1.0",
+    "description": "First visual composition; full reference exhibit acceptance remains Phase 9."
+  },
+  "runtime": {
+    "seed": 42
+  },
+  "visuals": {
+    "scene": {
+      "coordinateSpace": "virtual",
+      "width": 960,
+      "height": 540,
+      "background": "#101d25"
+    },
+    "systems": {
+      "landscape": {
+        "type": "graphic",
+        "content": {
+          "sky": {
+            "type": "rectangle",
+            "size": {
+              "width": 960,
+              "height": 540
+            },
+            "style": {
+              "fill": {
+                "type": "linear-gradient",
+                "from": {
+                  "x": 0,
+                  "y": 0
+                },
+                "to": {
+                  "x": 0,
+                  "y": 540
+                },
+                "stops": [
+                  {
+                    "offset": 0,
+                    "color": "#aabcb8"
+                  },
+                  {
+                    "offset": 1,
+                    "color": "#eddcb0"
+                  }
+                ]
+              }
+            }
+          },
+          "sun": {
+            "type": "ellipse",
+            "position": {
+              "x": 735,
+              "y": 120
+            },
+            "radius": 48,
+            "style": {
+              "fill": "#fff1c6"
+            }
+          },
+          "far": {
+            "type": "polygon",
+            "points": [
+              {
+                "x": 0,
+                "y": 390
+              },
+              {
+                "x": 220,
+                "y": 150
+              },
+              {
+                "x": 470,
+                "y": 340
+              },
+              {
+                "x": 660,
+                "y": 200
+              },
+              {
+                "x": 960,
+                "y": 410
+              },
+              {
+                "x": 960,
+                "y": 540
+              },
+              {
+                "x": 0,
+                "y": 540
+              }
+            ],
+            "style": {
+              "fill": "#667e72"
+            }
+          },
+          "near": {
+            "type": "spline",
+            "closed": true,
+            "points": [
+              {
+                "x": 0,
+                "y": 450
+              },
+              {
+                "x": 250,
+                "y": 320
+              },
+              {
+                "x": 580,
+                "y": 480
+              },
+              {
+                "x": 960,
+                "y": 380
+              },
+              {
+                "x": 960,
+                "y": 600
+              },
+              {
+                "x": 0,
+                "y": 600
+              }
+            ],
+            "style": {
+              "fill": "#314c41"
+            }
+          }
+        }
+      },
+      "rain": {
+        "type": "particles",
+        "count": 240,
+        "capacity": 256,
+        "distribution": {
+          "type": "uniform",
+          "min": {
+            "x": 0,
+            "y": 0
+          },
+          "max": {
+            "x": 960,
+            "y": 540
+          }
+        },
+        "render": {
+          "type": "line",
+          "to": {
+            "x": -3,
+            "y": 15
+          },
+          "style": {
+            "stroke": "#90acba",
+            "strokeWidth": 1,
+            "opacity": 0.6
+          }
+        },
+        "velocity": {
+          "x": -35,
+          "y": 220
+        },
+        "behaviors": [
+          {
+            "type": "wrap",
+            "bounds": "scene"
+          }
+        ]
+      }
+    }
+  }
+}
diff --git a/exhibits/exhibit-d.xzbt b/exhibits/exhibit-d.xzbt
new file mode 100644
index 0000000..0969776
--- /dev/null
+++ b/exhibits/exhibit-d.xzbt
@@ -0,0 +1,172 @@
+{
+  "xzbt": "0.1",
+  "meta": {
+    "id": "exhibit-d",
+    "name": "Exhibit D — Instrument Display",
+    "version": "0.1.0",
+    "description": "First visual composition; full reference exhibit acceptance remains Phase 9."
+  },
+  "runtime": {
+    "seed": 42
+  },
+  "visuals": {
+    "scene": {
+      "coordinateSpace": "virtual",
+      "width": 960,
+      "height": 540,
+      "background": "#101d25"
+    },
+    "systems": {
+      "rings": {
+        "type": "graphic",
+        "content": {
+          "a": {
+            "type": "ring",
+            "position": {
+              "x": 480,
+              "y": 270
+            },
+            "radius": 70,
+            "innerRadius": 68,
+            "style": {
+              "fill": "#72c4bd"
+            }
+          },
+          "b": {
+            "type": "ring",
+            "position": {
+              "x": 480,
+              "y": 270
+            },
+            "radius": 130,
+            "innerRadius": 128,
+            "style": {
+              "fill": "#72c4bd"
+            }
+          },
+          "c": {
+            "type": "ring",
+            "position": {
+              "x": 480,
+              "y": 270
+            },
+            "radius": 190,
+            "innerRadius": 188,
+            "style": {
+              "fill": "#72c4bd"
+            }
+          },
+          "label": {
+            "type": "text",
+            "text": "FIELD / 04",
+            "position": {
+              "x": 35,
+              "y": 45
+            },
+            "size": 18,
+            "style": {
+              "fill": "#a7d3c4"
+            }
+          },
+          "sweep": {
+            "type": "group",
+            "position": {
+              "x": 480,
+              "y": 270
+            },
+            "behaviors": [
+              {
+                "type": "rotate",
+                "speed": 40
+              }
+            ],
+            "children": {
+              "ray": {
+                "type": "line",
+                "to": {
+                  "x": 188,
+                  "y": 0
+                },
+                "style": {
+                  "stroke": "#ddf6a0",
+                  "strokeWidth": 3
+                }
+              }
+            }
+          }
+        },
+        "layer": "display"
+      },
+      "ticks": {
+        "type": "repeater",
+        "count": 48,
+        "distribution": {
+          "type": "ring",
+          "center": {
+            "x": 480,
+            "y": 270
+          },
+          "radius": 210,
+          "innerRadius": 209,
+          "mode": "even"
+        },
+        "repeat": {
+          "type": "point",
+          "style": {
+            "fill": "#789f95",
+            "pointSize": 3
+          }
+        },
+        "layer": "display"
+      },
+      "contacts": {
+        "type": "particles",
+        "count": 18,
+        "capacity": 32,
+        "distribution": {
+          "type": "ellipse",
+          "center": {
+            "x": 480,
+            "y": 270
+          },
+          "radius": 170
+        },
+        "render": {
+          "type": "point",
+          "style": {
+            "fill": "#d8e6a7",
+            "pointSize": 5
+          }
+        },
+        "behaviors": [
+          {
+            "type": "twinkle",
+            "min": 0.2,
+            "max": 1,
+            "rate": 0.6
+          }
+        ],
+        "layer": "display"
+      }
+    },
+    "layers": {
+      "display": {}
+    }
+  },
+  "state": {
+    "level": {
+      "type": "number",
+      "initial": 0.7,
+      "min": 0,
+      "max": 1
+    }
+  },
+  "bindings": [
+    {
+      "source": "state.level",
+      "target": "visuals.layers.display.opacity",
+      "scale": 0.7,
+      "offset": 0.3
+    }
+  ]
+}
diff --git a/exhibits/visual-challenges/audio-reactive.xzbt b/exhibits/visual-challenges/audio-reactive.xzbt
new file mode 100644
index 0000000..17ced25
--- /dev/null
+++ b/exhibits/visual-challenges/audio-reactive.xzbt
@@ -0,0 +1,91 @@
+{
+  "xzbt": "0.1",
+  "meta": {
+    "id": "audio-reactive",
+    "name": "Audio-reactive visualization",
+    "version": "1.0.0",
+    "description": "PRD 130 challenge 12; generic visual primitives only."
+  },
+  "runtime": {
+    "seed": 4211
+  },
+  "visuals": {
+    "scene": {
+      "coordinateSpace": "virtual",
+      "width": 960,
+      "height": 540,
+      "background": "#101d25"
+    },
+    "layers": {
+      "field": {}
+    },
+    "systems": {
+      "network": {
+        "type": "particles",
+        "count": 65,
+        "capacity": 96,
+        "distribution": {
+          "type": "rectangle",
+          "center": {
+            "x": 480,
+            "y": 270
+          },
+          "size": {
+            "width": 800,
+            "height": 410
+          }
+        },
+        "render": {
+          "type": "point",
+          "style": {
+            "fill": "#d8e9f5",
+            "pointSize": 4
+          }
+        },
+        "links": {
+          "rule": "nearest",
+          "count": 3,
+          "maxDistance": 180,
+          "maxLinks": 160,
+          "fadeWithDistance": true,
+          "style": {
+            "stroke": "#6899b7",
+            "strokeWidth": 1
+          }
+        },
+        "behaviors": [
+          {
+            "type": "noise-displace",
+            "amplitude": {
+              "x": 25,
+              "y": 25
+            },
+            "scale": 120,
+            "speed": 0.1
+          }
+        ],
+        "layer": "field"
+      }
+    },
+    "effects": [
+      {
+        "type": "bloom",
+        "intensity": 0.4
+      }
+    ]
+  },
+  "bindings": [
+    {
+      "source": "signals.audio.energy",
+      "target": "visuals.layers.field.opacity",
+      "scale": 0.8,
+      "offset": 0.2
+    },
+    {
+      "source": "signals.audio.low",
+      "target": "visuals.camera.zoom",
+      "scale": 0.25,
+      "offset": 1
+    }
+  ]
+}
diff --git a/exhibits/visual-challenges/constellation-network.xzbt b/exhibits/visual-challenges/constellation-network.xzbt
new file mode 100644
index 0000000..11b0a87
--- /dev/null
+++ b/exhibits/visual-challenges/constellation-network.xzbt
@@ -0,0 +1,67 @@
+{
+  "xzbt": "0.1",
+  "meta": {
+    "id": "constellation-network",
+    "name": "Constellation network",
+    "version": "1.0.0",
+    "description": "PRD 130 challenge 8; generic visual primitives only."
+  },
+  "runtime": {
+    "seed": 4207
+  },
+  "visuals": {
+    "scene": {
+      "coordinateSpace": "virtual",
+      "width": 960,
+      "height": 540,
+      "background": "#101d25"
+    },
+    "systems": {
+      "network": {
+        "type": "particles",
+        "count": 65,
+        "capacity": 96,
+        "distribution": {
+          "type": "rectangle",
+          "center": {
+            "x": 480,
+            "y": 270
+          },
+          "size": {
+            "width": 800,
+            "height": 410
+          }
+        },
+        "render": {
+          "type": "point",
+          "style": {
+            "fill": "#d8e9f5",
+            "pointSize": 4
+          }
+        },
+        "links": {
+          "rule": "nearest",
+          "count": 3,
+          "maxDistance": 180,
+          "maxLinks": 160,
+          "fadeWithDistance": true,
+          "style": {
+            "stroke": "#6899b7",
+            "strokeWidth": 1
+          }
+        },
+        "behaviors": [
+          {
+            "type": "noise-displace",
+            "amplitude": {
+              "x": 25,
+              "y": 25
+            },
+            "scale": 120,
+            "speed": 0.1
+          }
+        ]
+      }
+    }
+  }
+}
diff --git a/exhibits/visual-challenges/deep-parallax-starfield.xzbt b/exhibits/visual-challenges/deep-parallax-starfield.xzbt
new file mode 100644
index 0000000..faefb82
--- /dev/null
+++ b/exhibits/visual-challenges/deep-parallax-starfield.xzbt
@@ -0,0 +1,113 @@
+{
+  "xzbt": "0.1",
+  "meta": {
+    "id": "deep-parallax-starfield",
+    "name": "Deep parallax starfield",
+    "version": "1.0.0",
+    "description": "PRD 130 challenge 1; generic visual primitives only."
+  },
+  "runtime": {
+    "seed": 4200
+  },
+  "visuals": {
+    "scene": {
+      "coordinateSpace": "virtual",
+      "width": 960,
+      "height": 540,
+      "background": "#101d25"
+    },
+    "layers": {
+      "far": {
+        "parallax": 0.2
+      },
+      "near": {
+        "parallax": 1
+      }
+    },
+    "camera": {
+      "projection": "perspective",
+      "focalLength": 1000
+    },
+    "automation": [
+      {
+        "target": "camera.x",
+        "loop": {
+          "mode": "ping-pong"
+        },
+        "interpolation": "smooth",
+        "points": [
+          {
+            "at": "0ms",
+            "value": 400
+          },
+          {
+            "at": "12s",
+            "value": 570
+          }
+        ]
+      }
+    ],
+    "systems": {
+      "far": {
+        "type": "particles",
+        "count": 250,
+        "capacity": 256,
+        "distribution": {
+          "type": "uniform",
+          "min": {
+            "x": 0,
+            "y": 0
+          },
+          "max": {
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+        "layer": "far",
+        "z": {
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+            "y": 540
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+        },
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+          "style": {
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+            "pointSize": 3
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+        },
+        "layer": "near",
+        "z": {
+          "random": {
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+            "max": 200
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+        }
+      }
+    }
+  }
+}
diff --git a/exhibits/visual-challenges/flow-field.xzbt b/exhibits/visual-challenges/flow-field.xzbt
new file mode 100644
index 0000000..fd2ee72
--- /dev/null
+++ b/exhibits/visual-challenges/flow-field.xzbt
@@ -0,0 +1,71 @@
+{
+  "xzbt": "0.1",
+  "meta": {
+    "id": "flow-field",
+    "name": "Fog or smoke-like flow field",
+    "version": "1.0.0",
+    "description": "PRD 130 challenge 2; generic visual primitives only."
+  },
+  "runtime": {
+    "seed": 4201
+  },
+  "visuals": {
+    "scene": {
+      "coordinateSpace": "virtual",
+      "width": 960,
+      "height": 540,
+      "background": "#101d25"
+    },
+    "fields": {
+      "flow": {
+        "type": "noise",
+        "mode": "curl",
+        "scale": 160,
+        "amplitude": 25,
+        "speed": 0.12
+      }
+    },
+    "systems": {
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+        "count": 150,
+        "capacity": 256,
+        "distribution": {
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+          "min": {
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+            "y": 0
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+          "max": {
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+            "y": 540
+          }
+        },
+        "render": {
+          "type": "ellipse",
+          "radius": 20,
+          "style": {
+            "fill": "#b5c1c0",
+            "opacity": 0.025
+          }
+        },
+        "fields": [
+          "flow"
+        ],
+        "drag": 0.2,
+        "behaviors": [
+          {
+            "type": "wrap",
+            "bounds": "scene"
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+        ]
+      }
+    },
+    "effects": [
+      {
+        "type": "blur",
+        "radius": 5
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+    ]
+  }
+}
diff --git a/exhibits/visual-challenges/instrument-display.xzbt b/exhibits/visual-challenges/instrument-display.xzbt
new file mode 100644
index 0000000..f2a3917
--- /dev/null
+++ b/exhibits/visual-challenges/instrument-display.xzbt
@@ -0,0 +1,150 @@
+{
+  "xzbt": "0.1",
+  "meta": {
+    "id": "instrument-display",
+    "name": "Instrument and radar display",
+    "version": "1.0.0",
+    "description": "PRD 130 challenge 7; generic visual primitives only."
+  },
+  "runtime": {
+    "seed": 4206
+  },
+  "visuals": {
+    "scene": {
+      "coordinateSpace": "virtual",
+      "width": 960,
+      "height": 540,
+      "background": "#101d25"
+    },
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+            "innerRadius": 68,
+            "style": {
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+              "y": 270
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+            "radius": 130,
+            "innerRadius": 128,
+            "style": {
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+              "y": 270
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+            "radius": 190,
+            "innerRadius": 188,
+            "style": {
+              "fill": "#72c4bd"
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+          },
+          "label": {
+            "type": "text",
+            "text": "FIELD / 04",
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+              "y": 45
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+            "style": {
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+          "mode": "even"
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+          "radius": 170
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+          "style": {
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+        },
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+  }
+}
diff --git a/exhibits/visual-challenges/mechanical-abstraction.xzbt b/exhibits/visual-challenges/mechanical-abstraction.xzbt
new file mode 100644
index 0000000..fad8586
--- /dev/null
+++ b/exhibits/visual-challenges/mechanical-abstraction.xzbt
@@ -0,0 +1,110 @@
+{
+  "xzbt": "0.1",
+  "meta": {
+    "id": "mechanical-abstraction",
+    "name": "Rotating mechanical abstraction",
+    "version": "1.0.0",
+    "description": "PRD 130 challenge 5; generic visual primitives only."
+  },
+  "runtime": {
+    "seed": 4204
+  },
+  "visuals": {
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+      "background": "#101d25"
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+            }
+          }
+        }
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+    }
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+}
diff --git a/exhibits/visual-challenges/morphing-art.xzbt b/exhibits/visual-challenges/morphing-art.xzbt
new file mode 100644
index 0000000..1b9aee0
--- /dev/null
+++ b/exhibits/visual-challenges/morphing-art.xzbt
@@ -0,0 +1,126 @@
+{
+  "xzbt": "0.1",
+  "meta": {
+    "id": "morphing-art",
+    "name": "Morphing geometric art",
+    "version": "1.0.0",
+    "description": "PRD 130 challenge 11; generic visual primitives only."
+  },
+  "runtime": {
+    "seed": 4210
+  },
+  "visuals": {
+    "scene": {
+      "coordinateSpace": "virtual",
+      "width": 960,
+      "height": 540,
+      "background": "#101d25"
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+                "to": "target",
+                "duration": "6s",
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+}
diff --git a/exhibits/visual-challenges/natural-abstraction.xzbt b/exhibits/visual-challenges/natural-abstraction.xzbt
new file mode 100644
index 0000000..c3b3f7f
--- /dev/null
+++ b/exhibits/visual-challenges/natural-abstraction.xzbt
@@ -0,0 +1,179 @@
+{
+  "xzbt": "0.1",
+  "meta": {
+    "id": "natural-abstraction",
+    "name": "Natural meadow abstraction",
+    "version": "1.0.0",
+    "description": "PRD 130 challenge 14; generic visual primitives only."
+  },
+  "runtime": {
+    "seed": 4213
+  },
+  "visuals": {
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+              "height": 540
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diff --git a/exhibits/visual-challenges/organic-pulse.xzbt b/exhibits/visual-challenges/organic-pulse.xzbt
new file mode 100644
index 0000000..ebea07a
--- /dev/null
+++ b/exhibits/visual-challenges/organic-pulse.xzbt
@@ -0,0 +1,102 @@
+{
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+  "meta": {
+    "id": "organic-pulse",
+    "name": "Organic pulsing structure",
+    "version": "1.0.0",
+    "description": "PRD 130 challenge 6; generic visual primitives only."
+  },
+  "runtime": {
+    "seed": 4205
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+  "visuals": {
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+      "coordinateSpace": "virtual",
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+      }
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+}
diff --git a/exhibits/visual-challenges/persistent-landscape.xzbt b/exhibits/visual-challenges/persistent-landscape.xzbt
new file mode 100644
index 0000000..aa54cf9
--- /dev/null
+++ b/exhibits/visual-challenges/persistent-landscape.xzbt
@@ -0,0 +1,137 @@
+{
+  "xzbt": "0.1",
+  "meta": {
+    "id": "persistent-landscape",
+    "name": "Persistent landscape",
+    "version": "1.0.0",
+    "description": "PRD 130 challenge 9; generic visual primitives only."
+  },
+  "runtime": {
+    "seed": 4208
+  },
+  "visuals": {
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+  }
+}
diff --git a/exhibits/visual-challenges/spline-network.xzbt b/exhibits/visual-challenges/spline-network.xzbt
new file mode 100644
index 0000000..7836a9a
--- /dev/null
+++ b/exhibits/visual-challenges/spline-network.xzbt
@@ -0,0 +1,381 @@
+{
+  "xzbt": "0.1",
+  "meta": {
+    "id": "spline-network",
+    "name": "Evolving spline network",
+    "version": "1.0.0",
+    "description": "PRD 130 challenge 3; generic visual primitives only."
+  },
+  "runtime": {
+    "seed": 4202
+  },
+  "visuals": {
+    "scene": {
+      "coordinateSpace": "virtual",
+      "width": 960,
+      "height": 540,
+      "background": "#101d25"
+    },
+    "systems": {
+      "curves": {
+        "type": "graphic",
+        "content": {
+          "c0": {
+            "type": "spline",
+            "points": [
+              {
+                "x": 100,
+                "y": 250
+              },
+              {
+                "x": 195,
+                "y": 344.2081569929845
+              },
+              {
+                "x": 290,
+                "y": 225.72359530745103
+              },
+              {
+                "x": 385,
+                "y": 162.0476051788654
+              },
+              {
+                "x": 480,
+                "y": 296.94076835816776
+              },
+              {
+                "x": 575,
+                "y": 325.85627569923156
+              },
+              {
+                "x": 670,
+                "y": 183.51190467861346
+              },
+              {
+                "x": 765,
+                "y": 191.27697433748185
+              },
+              {
+                "x": 860,
+                "y": 331.6203724113671
+              }
+            ],
+            "style": {
+              "stroke": "#82b7c7",
+              "strokeWidth": 2
+            },
+            "position": {
+              "x": 0,
+              "y": -105
+            },
+            "behaviors": [
+              {
+                "type": "point-wander",
+                "amplitude": {
+                  "x": 30,
+                  "y": 45
+                },
+                "rate": 0.13
+              }
+            ]
+          },
+          "c1": {
+            "type": "spline",
+            "points": [
+              {
+                "x": 100,
+                "y": 250
+              },
+              {
+                "x": 195,
+                "y": 344.2081569929845
+              },
+              {
+                "x": 290,
+                "y": 225.72359530745103
+              },
+              {
+                "x": 385,
+                "y": 162.0476051788654
+              },
+              {
+                "x": 480,
+                "y": 296.94076835816776
+              },
+              {
+                "x": 575,
+                "y": 325.85627569923156
+              },
+              {
+                "x": 670,
+                "y": 183.51190467861346
+              },
+              {
+                "x": 765,
+                "y": 191.27697433748185
+              },
+              {
+                "x": 860,
+                "y": 331.6203724113671
+              }
+            ],
+            "style": {
+              "stroke": "#82b7c7",
+              "strokeWidth": 2
+            },
+            "position": {
+              "x": 0,
+              "y": -70
+            },
+            "behaviors": [
+              {
+                "type": "point-wander",
+                "amplitude": {
+                  "x": 30,
+                  "y": 45
+                },
+                "rate": 0.13
+              }
+            ]
+          },
+          "c2": {
+            "type": "spline",
+            "points": [
+              {
+                "x": 100,
+                "y": 250
+              },
+              {
+                "x": 195,
+                "y": 344.2081569929845
+              },
+              {
+                "x": 290,
+                "y": 225.72359530745103
+              },
+              {
+                "x": 385,
+                "y": 162.0476051788654
+              },
+              {
+                "x": 480,
+                "y": 296.94076835816776
+              },
+              {
+                "x": 575,
+                "y": 325.85627569923156
+              },
+              {
+                "x": 670,
+                "y": 183.51190467861346
+              },
+              {
+                "x": 765,
+                "y": 191.27697433748185
+              },
+              {
+                "x": 860,
+                "y": 331.6203724113671
+              }
+            ],
+            "style": {
+              "stroke": "#82b7c7",
+              "strokeWidth": 2
+            },
+            "position": {
+              "x": 0,
+              "y": -35
+            },
+            "behaviors": [
+              {
+                "type": "point-wander",
+                "amplitude": {
+                  "x": 30,
+                  "y": 45
+                },
+                "rate": 0.13
+              }
+            ]
+          },
+          "c3": {
+            "type": "spline",
+            "points": [
+              {
+                "x": 100,
+                "y": 250
+              },
+              {
+                "x": 195,
+                "y": 344.2081569929845
+              },
+              {
+                "x": 290,
+                "y": 225.72359530745103
+              },
+              {
+                "x": 385,
+                "y": 162.0476051788654
+              },
+              {
+                "x": 480,
+                "y": 296.94076835816776
+              },
+              {
+                "x": 575,
+                "y": 325.85627569923156
+              },
+              {
+                "x": 670,
+                "y": 183.51190467861346
+              },
+              {
+                "x": 765,
+                "y": 191.27697433748185
+              },
+              {
+                "x": 860,
+                "y": 331.6203724113671
+              }
+            ],
+            "style": {
+              "stroke": "#82b7c7",
+              "strokeWidth": 2
+            },
+            "position": {
+              "x": 0,
+              "y": 0
+            },
+            "behaviors": [
+              {
+                "type": "point-wander",
+                "amplitude": {
+                  "x": 30,
+                  "y": 45
+                },
+                "rate": 0.13
+              }
+            ]
+          },
+          "c4": {
+            "type": "spline",
+            "points": [
+              {
+                "x": 100,
+                "y": 250
+              },
+              {
+                "x": 195,
+                "y": 344.2081569929845
+              },
+              {
+                "x": 290,
+                "y": 225.72359530745103
+              },
+              {
+                "x": 385,
+                "y": 162.0476051788654
+              },
+              {
+                "x": 480,
+                "y": 296.94076835816776
+              },
+              {
+                "x": 575,
+                "y": 325.85627569923156
+              },
+              {
+                "x": 670,
+                "y": 183.51190467861346
+              },
+              {
+                "x": 765,
+                "y": 191.27697433748185
+              },
+              {
+                "x": 860,
+                "y": 331.6203724113671
+              }
+            ],
+            "style": {
+              "stroke": "#82b7c7",
+              "strokeWidth": 2
+            },
+            "position": {
+              "x": 0,
+              "y": 35
+            },
+            "behaviors": [
+              {
+                "type": "point-wander",
+                "amplitude": {
+                  "x": 30,
+                  "y": 45
+                },
+                "rate": 0.13
+              }
+            ]
+          },
+          "c5": {
+            "type": "spline",
+            "points": [
+              {
+                "x": 100,
+                "y": 250
+              },
+              {
+                "x": 195,
+                "y": 344.2081569929845
+              },
+              {
+                "x": 290,
+                "y": 225.72359530745103
+              },
+              {
+                "x": 385,
+                "y": 162.0476051788654
+              },
+              {
+                "x": 480,
+                "y": 296.94076835816776
+              },
+              {
+                "x": 575,
+                "y": 325.85627569923156
+              },
+              {
+                "x": 670,
+                "y": 183.51190467861346
+              },
+              {
+                "x": 765,
+                "y": 191.27697433748185
+              },
+              {
+                "x": 860,
+                "y": 331.6203724113671
+              }
+            ],
+            "style": {
+              "stroke": "#82b7c7",
+              "strokeWidth": 2
+            },
+            "position": {
+              "x": 0,
+              "y": 70
+            },
+            "behaviors": [
+              {
+                "type": "point-wander",
+                "amplitude": {
+                  "x": 30,
+                  "y": 45
+                },
+                "rate": 0.13
+              }
+            ]
+          }
+        }
+      }
+    }
+  }
+}
diff --git a/exhibits/visual-challenges/transient-impact.xzbt b/exhibits/visual-challenges/transient-impact.xzbt
new file mode 100644
index 0000000..f7c6f2a
--- /dev/null
+++ b/exhibits/visual-challenges/transient-impact.xzbt
@@ -0,0 +1,78 @@
+{
+  "xzbt": "0.1",
+  "meta": {
+    "id": "transient-impact",
+    "name": "Transient impact burst",
+    "version": "1.0.0",
+    "description": "PRD 130 challenge 10; generic visual primitives only."
+  },
+  "runtime": {
+    "seed": 4209
+  },
+  "visuals": {
+    "scene": {
+      "coordinateSpace": "virtual",
+      "width": 960,
+      "height": 540,
+      "background": "#101d25"
+    },
+    "systems": {
+      "burst": {
+        "type": "particles",
+        "lifecycle": "spawned",
+        "spawn": {
+          "lifetime": "2s",
+          "release": "1s"
+        },
+        "count": 120,
+        "capacity": 128,
+        "distribution": {
+          "type": "point",
+          "position": {
+            "x": 480,
+            "y": 270
+          }
+        },
+        "velocity": {
+          "x": {
+            "random": {
+              "min": -160,
+              "max": 160
+            }
+          },
+          "y": {
+            "random": {
+              "min": -160,
+              "max": 160
+            }
+          }
+        },
+        "lifetime": "3s",
+        "size": {
+          "from": 1.5,
+          "to": 0.1
+        },
+        "opacity": {
+          "from": 1,
+          "to": 0
+        },
+        "render": {
+          "type": "point",
+          "style": {
+            "fill": "#f5c276",
+            "pointSize": 4
+          }
+        },
+        "trail": {
+          "length": 20,
+          "mode": "line",
+          "width": 2,
+          "style": {
+            "stroke": "#d98963",
+            "strokeWidth": 2
+          }
+        }
+      }
+    }
+  }
+}
diff --git a/exhibits/visual-challenges/weather-particles.xzbt b/exhibits/visual-challenges/weather-particles.xzbt
new file mode 100644
index 0000000..2f020d1
--- /dev/null
+++ b/exhibits/visual-challenges/weather-particles.xzbt
@@ -0,0 +1,60 @@
+{
+  "xzbt": "0.1",
+  "meta": {
+    "id": "weather-particles",
+    "name": "Rain particles",
+    "version": "1.0.0",
+    "description": "PRD 130 challenge 4; generic visual primitives only."
+  },
+  "runtime": {
+    "seed": 4203
+  },
+  "visuals": {
+    "scene": {
+      "coordinateSpace": "virtual",
+      "width": 960,
+      "height": 540,
+      "background": "#101d25"
+    },
+    "systems": {
+      "rain": {
+        "type": "particles",
+        "count": 240,
+        "capacity": 256,
+        "distribution": {
+          "type": "uniform",
+          "min": {
+            "x": 0,
+            "y": 0
+          },
+          "max": {
+            "x": 960,
+            "y": 540
+          }
+        },
+        "render": {
+          "type": "line",
+          "to": {
+            "x": -3,
+            "y": 15
+          },
+          "style": {
+            "stroke": "#90acba",
+            "strokeWidth": 1,
+            "opacity": 0.6
+          }
+        },
+        "velocity": {
+          "x": -35,
+          "y": 220
+        },
+        "behaviors": [
+          {
+            "type": "wrap",
+            "bounds": "scene"
+          }
+        ]
+      }
+    }
+  }
+}
diff --git a/exhibits/visual-challenges/window-traffic.xzbt b/exhibits/visual-challenges/window-traffic.xzbt
new file mode 100644
index 0000000..70fb8a3
--- /dev/null
+++ b/exhibits/visual-challenges/window-traffic.xzbt
@@ -0,0 +1,130 @@
+{
+  "xzbt": "0.1",
+  "meta": {
+    "id": "window-traffic",
+    "name": "Window containing procedural traffic",
+    "version": "1.0.0",
+    "description": "PRD 130 challenge 13; generic visual primitives only."
+  },
+  "runtime": {
+    "seed": 4212
+  },
+  "visuals": {
+    "scene": {
+      "coordinateSpace": "virtual",
+      "width": 960,
+      "height": 540,
+      "background": "#101d25"
+    },
+    "systems": {
+      "background": {
+        "type": "graphic",
+        "content": {
+          "wall": {
+            "type": "rectangle",
+            "size": {
+              "width": 960,
+              "height": 540
+            },
+            "style": {
+              "fill": "#c8b69c"
+            }
+          },
+          "window": {
+            "type": "rectangle",
+            "position": {
+              "x": 150,
+              "y": 90
+            },
+            "size": {
+              "width": 660,
+              "height": 360
+            },
+            "style": {
+              "fill": "#273f49"
+            }
+          }
+        }
+      },
+      "traffic": {
+        "type": "repeater",
+        "count": 14,
+        "distribution": {
+          "type": "grid",
+          "columns": 7,
+          "rows": 2,
+          "origin": {
+            "x": 185,
+            "y": 235
+          },
+          "spacing": {
+            "x": 88,
+            "y": 75
+          }
+        },
+        "repeat": {
+          "type": "rectangle",
+          "size": {
+            "width": 24,
+            "height": 8
+          },
+          "style": {
+            "fill": "#eed092"
+          },
+          "behaviors": [
+            {
+              "type": "drift",
+              "velocity": {
+                "x": 20,
+                "y": 0
+              }
+            },
+            {
+              "type": "wrap",
+              "bounds": {
+                "x": -30,
+                "y": -30,
+                "width": 60,
+                "height": 60
+              }
+            }
+          ]
+        }
+      },
+      "frame": {
+        "type": "graphic",
+        "content": {
+          "mullion": {
+            "type": "rectangle",
+            "position": {
+              "x": 470,
+              "y": 85
+            },
+            "size": {
+              "width": 12,
+              "height": 370
+            },
+            "style": {
+              "fill": "#d8c8af"
+            }
+          },
+          "border": {
+            "type": "rectangle",
+            "position": {
+              "x": 145,
+              "y": 85
+            },
+            "size": {
+              "width": 670,
+              "height": 370
+            },
+            "style": {
+              "stroke": "#e8d8bf",
+              "strokeWidth": 12
+            }
+          }
+        }
+      }
+    }
+  }
+}
diff --git a/test/phase4-challenges.test.mjs b/test/phase4-challenges.test.mjs
new file mode 100644
index 0000000..40d4a77
--- /dev/null
+++ b/test/phase4-challenges.test.mjs
@@ -0,0 +1,55 @@
+import test from 'node:test';
+import assert from 'node:assert/strict';
+import { visualChallenges, visualExhibits } from '../tools/visual-challenge-fixtures.mjs';
+import { validateExhibit } from '../src/runtime/validator.js';
+import { VisualEngine } from '../src/runtime/visual-engine.js';
+import { ResolutionEngine } from '../src/runtime/resolution.js';
+import { SeededRNG } from '../src/runtime/rng.js';
+import { Script } from 'node:vm';
+import { readFileSync } from 'node:fs';
+import { buildVisualAcceptance } from '../tools/build-visual-acceptance.mjs';
+
+for (const fixture of [...visualChallenges, ...visualExhibits]) test(`4g ${fixture.id}: validates, executes, draws, and reproduces across frame rates`, () => {
+  assert.deepEqual(validateExhibit(fixture.document).errors, []);
+  const run = cadence => {
+    const rng = new SeededRNG(fixture.document.runtime.seed);
+    const resolution = new ResolutionEngine(fixture.document, rng);
+    const engine = new VisualEngine(fixture.document, { rng, resolution });
+    if (fixture.id === 'transient-impact') engine.spawn('burst');
+    let plan;
+    for (let i = 0; i < 120; i++) {
+      resolution.signals.set('signals.audio.energy', (Math.sin(i / 20) + 1) / 2);
+      resolution.signals.set('signals.audio.low', (Math.cos(i / 30) + 1) / 2);
+      resolution.advance(1000 / 60); engine.advance(1000 / 60);
+      if (i % cadence === 0 || i === 119) plan = engine.planFrame({ width: 960, height: 540 });
+    }
+    assert.equal(plan.deferred.length, 0);
+    assert.ok(plan.layers.some(layer => layer.nodes.length > 0));
+    const finite = object => {
+      if (typeof object === 'number') assert.ok(Number.isFinite(object));
+      else if (object && typeof object === 'object') for (const value of Object.values(object)) finite(value);
+    };
+    finite(plan.layers);
+    engine.dispose(); assert.equal(engine.instances.size, 0); assert.equal(resolution.automation.size, 0);
+    return plan.layers;
+  };
+  assert.deepEqual(run(1), run(4));
+});
+
+test('4g standalone acceptance build is deterministic, contains every fixture and parses as JavaScript', () => {
+  const first = buildVisualAcceptance(), second = buildVisualAcceptance();
+  assert.equal(first.html, second.html); assert.equal(first.count, 18);
+  const script = /<script>([\s\S]*)<\/script>/.exec(first.html)[1];
+  assert.doesNotThrow(() => new Script(script));
+  assert.ok(!/<script[^>]+src=|<link[^>]+href=/.test(first.html));
+  for (const fixture of visualChallenges) assert.deepEqual(JSON.parse(readFileSync(new URL(`../exhibits/visual-challenges/${fixture.id}.xzbt`, import.meta.url))), fixture.document);
+});
+
+test('C6: standalone CLI validator accepts all visual challenges and exhibits', async () => {
+  const { ExhibitValidator } = await import('../tools/validate-exhibit.mjs');
+  for (const fixture of [...visualChallenges, ...visualExhibits]) {
+    const validator = new ExhibitValidator(fixture.document, `${fixture.id}.xzbt`);
+    const result = validator.validate();
+    assert.deepEqual(result.errors, [], `CLI validator errors on ${fixture.id}: ${JSON.stringify(result.errors)}`);
+  }
+});
diff --git a/tools/validate-exhibit.mjs b/tools/validate-exhibit.mjs
index cdb2338..1806705 100644
--- a/tools/validate-exhibit.mjs
+++ b/tools/validate-exhibit.mjs
@@ -9,6 +9,9 @@
 import { readFileSync } from 'node:fs';
 import { resolve } from 'node:path';
 import { validateAudioSubsystem } from '../src/runtime/audio-graph.js';
+import { validateCadenceSubsystem } from '../src/runtime/cadence-validation.js';
+import { matchVisualTarget } from '../src/runtime/visual-contract.js';
+import { validateVisualSubsystem } from '../src/runtime/visual-validation.js';
 
 const ID_REGEX = /^[a-z][a-z0-9_-]*$/;
 const REF_PATH_REGEX = /^[a-z][a-z0-9_-]*(\.[a-z][a-z0-9_-]*)+$/;
@@ -159,6 +162,19 @@ export class ExhibitValidator {
       pushError: (errors, code, path, message) => errors.push({ code, path, message })
     });
 
+    // 8. Visual subsystem (Format Specification sections 17-19)
+    validateVisualSubsystem(this.doc, this.errors, {
+      validateValueSpec: (unusedDocument, spec, path, unusedErrors, scope) => this.validateValueSpec(spec, path, scope),
+      pushError: (errors, code, path, message) => errors.push({ code, path, message })
+    });
+
+    // 9. Cadence and Event subsystems (Format Specification section 20)
+    validateCadenceSubsystem(this.doc, this.errors, {
+      validateValueSpec: (unusedDocument, spec, path, unusedErrors, scope) => this.validateValueSpec(spec, path, scope),
+      validateCondition: (unusedDocument, cond, path, unusedErrors) => this.validateConditionSpec(cond, path),
+      pushError: (errors, code, path, message) => errors.push({ code, path, message })
+    });
+
     return this.getResult();
   }
 
@@ -449,7 +465,7 @@ export class ExhibitValidator {
         this.resolveReference(binding.source, `${path}.source`);
       }
 
-      if (typeof binding.target !== 'string' || !REF_PATH_REGEX.test(binding.target)) {
+      if (typeof binding.target !== 'string') {
         this.addError('ERR_INVALID_REFERENCE', `${path}.target`, `Invalid target reference: '${binding.target}'.`);
       } else {
         this.validateBindingTarget(binding.target, `${path}.target`);
@@ -569,6 +585,16 @@ export class ExhibitValidator {
       return;
     }
 
+    const visual = matchVisualTarget(this.doc, refPath);
+    if (visual) {
+      if (visual.reason === 'reference') {
+        this.addError('ERR_INVALID_REFERENCE', location, `Binding target '${refPath}' does not resolve.`);
+      } else if (visual.reason === 'unsupported') {
+        this.addError('ERR_UNSUPPORTED_TARGET', location, `Binding target '${refPath}' is not exposed. Per-object visual properties are not externally addressable in 0.1.`);
+      }
+      return;
+    }
+
     this.addError('ERR_UNSUPPORTED_TARGET', location, `Target '${refPath}' is not exposed by the shared 0.1 target registry.`);
   }
 
@@ -580,6 +606,8 @@ export class ExhibitValidator {
     if (parts[0] === 'audio' && parts[1] === 'buses' && parts[3] === 'gain') return 'number';
     if (parts[0] === 'signals') return RUNTIME_SIGNAL_TYPES.get(refPath) || null;
     if (parts[0] === 'modulators') return 'number';
+    const visual = matchVisualTarget(this.doc, refPath);
+    if (visual && !visual.reason) return visual.spec?.type || 'number';
     return null;
   }
 
diff --git a/tools/visual-challenge-fixtures.mjs b/tools/visual-challenge-fixtures.mjs
new file mode 100644
index 0000000..7b8df97
--- /dev/null
+++ b/tools/visual-challenge-fixtures.mjs
@@ -0,0 +1,91 @@
+// Authored exhibit data only. Subject names occur here, never in renderer dispatch.
+const random = (min, max) => ({ random: { min, max } });
+const dot = (color = '#cfe8ff', size = 3) => ({ type: 'point', style: { fill: color, pointSize: size } });
+const lineStyle = { stroke: '#82b7c7', strokeWidth: 2 };
+const graphic = content => ({ type: 'graphic', content });
+const ring = (radius, color = '#72c4bd') => ({ type: 'ring', position: { x: 480, y: 270 }, radius, innerRadius: radius - 2, style: { fill: color } });
+const auto = (target, from, to, duration = '12s') => ({ target, loop: { mode: 'ping-pong' }, interpolation: 'smooth', points: [{ at: '0ms', value: from }, { at: duration, value: to }] });
+const uniform = { type: 'uniform', min: { x: 0, y: 0 }, max: { x: 960, y: 540 } };
+const particles = (extra = {}) => ({ type: 'particles', count: 180, capacity: 256, distribution: uniform, render: dot(), ...extra });
+const splinePoints = Array.from({ length: 9 }, (_, i) => ({ x: 100 + i * 95, y: 250 + Math.sin(i * 1.7) * 95 }));
+const curve = { type: 'spline', points: splinePoints, style: lineStyle };
+const wrap = { type: 'wrap', bounds: 'scene' };
+const rain = particles({ count: 240, velocity: { x: -35, y: 220 }, render: { type: 'line', to: { x: -3, y: 15 }, style: { stroke: '#90acba', strokeWidth: 1, opacity: 0.6 } }, behaviors: [wrap] });
+const landscape = graphic({
+  sky: { type: 'rectangle', size: { width: 960, height: 540 }, style: { fill: { type: 'linear-gradient', from: { x: 0, y: 0 }, to: { x: 0, y: 540 }, stops: [{ offset: 0, color: '#aabcb8' }, { offset: 1, color: '#eddcb0' }] } } },
+  sun: { type: 'ellipse', position: { x: 735, y: 120 }, radius: 48, style: { fill: '#fff1c6' } },
+  far: { type: 'polygon', points: [{ x: 0, y: 390 }, { x: 220, y: 150 }, { x: 470, y: 340 }, { x: 660, y: 200 }, { x: 960, y: 410 }, { x: 960, y: 540 }, { x: 0, y: 540 }], style: { fill: '#667e72' } },
+  near: { type: 'spline', closed: true, points: [{ x: 0, y: 450 }, { x: 250, y: 320 }, { x: 580, y: 480 }, { x: 960, y: 380 }, { x: 960, y: 600 }, { x: 0, y: 600 }], style: { fill: '#314c41' } }
+});
+const machine = {
+  wheel: graphic({ outer: ring(160), inner: ring(125, '#e1bd7c'), hub: ring(38, '#e1bd7c') }),
+  spokes: { type: 'repeater', count: 12, distribution: { type: 'point', position: { x: 480, y: 270 } }, repeat: {
+    type: 'group', transform: { rotation: { op: 'multiply', args: [{ ref: 'repeat.fraction' }, 330] } }, behaviors: [{ type: 'rotate', speed: 12 }],
+    children: { bar: { type: 'rectangle', position: { x: 40, y: -4 }, size: { width: 85, height: 8 }, style: { fill: '#e1bd7c' } } }
+  } }
+};
+const radar = {
+  rings: graphic({ a: ring(70), b: ring(130), c: ring(190),
+    label: { type: 'text', text: 'FIELD / 04', position: { x: 35, y: 45 }, size: 18, style: { fill: '#a7d3c4' } },
+    sweep: { type: 'group', position: { x: 480, y: 270 }, behaviors: [{ type: 'rotate', speed: 40 }], children: { ray: { type: 'line', to: { x: 188, y: 0 }, style: { stroke: '#ddf6a0', strokeWidth: 3 } } } }
+  }),
+  ticks: { type: 'repeater', count: 48, distribution: { type: 'ring', center: { x: 480, y: 270 }, radius: 210, innerRadius: 209, mode: 'even' }, repeat: dot('#789f95', 3) },
+  contacts: particles({ count: 18, capacity: 32, distribution: { type: 'ellipse', center: { x: 480, y: 270 }, radius: 170 }, render: dot('#d8e6a7', 5), behaviors: [{ type: 'twinkle', min: 0.2, max: 1, rate: 0.6 }] })
+};
+const organic = graphic({ body: { type: 'spline', closed: true,
+  points: Array.from({ length: 12 }, (_, i) => ({ x: 480 + Math.cos(i * Math.PI / 6) * (110 + i % 3 * 23), y: 270 + Math.sin(i * Math.PI / 6) * 125 })),
+  style: { fill: '#537a63', stroke: '#acd2a0', strokeWidth: 3 },
+  behaviors: [{ type: 'point-wander', amplitude: { x: 28, y: 28 }, rate: 0.15 }, { type: 'pulse', property: 'style.opacity', amplitude: -0.35, frequency: 0.2 }]
+} });
+const network = particles({ count: 65, capacity: 96, distribution: { type: 'rectangle', center: { x: 480, y: 270 }, size: { width: 800, height: 410 } },
+  links: { rule: 'nearest', count: 3, maxDistance: 180, maxLinks: 160, fadeWithDistance: true, style: { stroke: '#6899b7', strokeWidth: 1 } },
+  behaviors: [{ type: 'noise-displace', amplitude: { x: 25, y: 25 }, scale: 120, speed: 0.1 }], render: dot('#d8e9f5', 4) });
+const morph = graphic({
+  shape: { ...curve, style: { stroke: '#ecbf85', strokeWidth: 4 }, behaviors: [{ type: 'morph', to: 'target', duration: '6s', loop: 'ping-pong' }] },
+  target: { ...curve, visible: false, points: splinePoints.map((p, i) => ({ x: p.x, y: 270 + Math.cos(i * 0.9) * 150 })) }
+});
+const burst = { type: 'particles', lifecycle: 'spawned', spawn: { lifetime: '2s', release: '1s' }, count: 120, capacity: 128,
+  distribution: { type: 'point', position: { x: 480, y: 270 } }, velocity: { x: random(-160, 160), y: random(-160, 160) },
+  lifetime: '3s', size: { from: 1.5, to: 0.1 }, opacity: { from: 1, to: 0 }, render: dot('#f5c276', 4),
+  trail: { length: 20, mode: 'line', width: 2, style: { stroke: '#d98963', strokeWidth: 2 } }
+};
+const definitions = [
+  ['deep-parallax-starfield', 'Deep parallax starfield', { layers: { far: { parallax: 0.2 }, near: { parallax: 1 } }, camera: { projection: 'perspective', focalLength: 1000 }, automation: [auto('camera.x', 400, 570)], systems: {
+    far: particles({ layer: 'far', count: 250, z: random(300, 1200), render: dot('#8c9ebf', 2) }), near: particles({ layer: 'near', count: 90, z: random(0, 200), render: dot('#ecdfc1', 3) }) } }],
+  ['flow-field', 'Fog or smoke-like flow field', { fields: { flow: { type: 'noise', mode: 'curl', scale: 160, amplitude: 25, speed: 0.12 } }, systems: { flow: particles({ count: 150, fields: ['flow'], drag: 0.2, render: { type: 'ellipse', radius: 20, style: { fill: '#b5c1c0', opacity: 0.025 } }, behaviors: [wrap] }) }, effects: [{ type: 'blur', radius: 5 }] }],
+  ['spline-network', 'Evolving spline network', { systems: { curves: graphic(Object.fromEntries(Array.from({ length: 6 }, (_, i) => [`c${i}`, { ...curve, position: { x: 0, y: (i - 3) * 35 }, behaviors: [{ type: 'point-wander', amplitude: { x: 30, y: 45 }, rate: 0.13 }] }]))) } }],
+  ['weather-particles', 'Rain particles', { systems: { rain } }],
+  ['mechanical-abstraction', 'Rotating mechanical abstraction', { systems: machine }],
+  ['organic-pulse', 'Organic pulsing structure', { systems: { organic } }],
+  ['instrument-display', 'Instrument and radar display', { systems: radar }],
+  ['constellation-network', 'Constellation network', { systems: { network } }],
+  ['persistent-landscape', 'Persistent landscape', { systems: { landscape } }],
+  ['transient-impact', 'Transient impact burst', { systems: { burst } }],
+  ['morphing-art', 'Morphing geometric art', { systems: { morph } }],
+  ['audio-reactive', 'Audio-reactive visualization', { layers: { field: {} }, systems: { network: { ...network, layer: 'field' } }, effects: [{ type: 'bloom', intensity: 0.4 }] }, { bindings: [{ source: 'signals.audio.energy', target: 'visuals.layers.field.opacity', scale: 0.8, offset: 0.2 }, { source: 'signals.audio.low', target: 'visuals.camera.zoom', scale: 0.25, offset: 1 }] }],
+  ['window-traffic', 'Window containing procedural traffic', { systems: {
+    background: graphic({ wall: { type: 'rectangle', size: { width: 960, height: 540 }, style: { fill: '#c8b69c' } }, window: { type: 'rectangle', position: { x: 150, y: 90 }, size: { width: 660, height: 360 }, style: { fill: '#273f49' } } }),
+    traffic: { type: 'repeater', count: 14, distribution: { type: 'grid', columns: 7, rows: 2, origin: { x: 185, y: 235 }, spacing: { x: 88, y: 75 } }, repeat: { type: 'rectangle', size: { width: 24, height: 8 }, style: { fill: '#eed092' }, behaviors: [{ type: 'drift', velocity: { x: 20, y: 0 } }, { type: 'wrap', bounds: { x: -30, y: -30, width: 60, height: 60 } }] } },
+    frame: graphic({ mullion: { type: 'rectangle', position: { x: 470, y: 85 }, size: { width: 12, height: 370 }, style: { fill: '#d8c8af' } }, border: { type: 'rectangle', position: { x: 145, y: 85 }, size: { width: 670, height: 370 }, style: { stroke: '#e8d8bf', strokeWidth: 12 } } })
+  } }],
+  ['natural-abstraction', 'Natural meadow abstraction', { systems: { landscape, seeds: particles({ count: 70, velocity: { x: 12, y: -4 }, render: dot('#e8daa5', 3), behaviors: [wrap, { type: 'noise-displace', amplitude: { x: 12, y: 24 }, scale: 100, speed: 0.1 }] }) } }]
+];
+
+export const visualChallenges = definitions.map(([id, name, visuals, extra], index) => ({
+  id, challenge: index + 1, document: { xzbt: '0.1', meta: { id, name, version: '1.0.0', description: `PRD 130 challenge ${index + 1}; generic visual primitives only.` }, runtime: { seed: 4200 + index },
+    visuals: { scene: { coordinateSpace: 'virtual', width: 960, height: 540, background: '#101d25' }, ...visuals }, ...extra }
+}));
+export const visualExhibits = [
+  ['exhibit-a', 'Exhibit A — Procedural Machine', { systems: machine }],
+  ['exhibit-b', 'Exhibit B — Deep Abstract Field', { systems: { network, morph }, effects: [{ type: 'bloom', radius: 5, intensity: 0.5 }] }],
+  ['exhibit-c', 'Exhibit C — Natural Environment', { systems: { landscape, rain } }],
+  ['exhibit-d', 'Exhibit D — Instrument Display', { systems: radar, layers: { display: {} } }]
+].map(([id, name, visuals]) => {
+  const document = { xzbt: '0.1', meta: { id, name, version: '0.1.0', description: 'First visual composition; full reference exhibit acceptance remains Phase 9.' }, runtime: { seed: 42 }, visuals: { scene: { coordinateSpace: 'virtual', width: 960, height: 540, background: '#101d25' }, ...structuredClone(visuals) } };
+  if (id === 'exhibit-d') {
+    for (const system of Object.values(document.visuals.systems)) system.layer = 'display';
+    document.state = { level: { type: 'number', initial: 0.7, min: 0, max: 1 } };
+    document.bindings = [{ source: 'state.level', target: 'visuals.layers.display.opacity', scale: 0.7, offset: 0.3 }];
+  }
+  return { id, document };
+});