Add identity-then-dog recipe

Chains identity effect followed by dog effect on cat input.
Demonstrates effect chaining: SOURCE → EFFECT → EFFECT → output

Since identity(cat) = cat, the result is dog(cat) = dog video.

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

mint_cat_copy.py

@@ -0,0 +1,140 @@
+#!/usr/bin/env python3
+"""
+Mint cat-copy.jpg by running the identity-cat recipe through artdag.
+
+Records full provenance: inputs, effects, software, hardware, owner.
+"""
+
+import hashlib
+import json
+import shutil
+import sys
+from datetime import datetime, timezone
+from pathlib import Path
+
+# Add artdag to path
+sys.path.insert(0, str(Path(__file__).parent.parent / "artdag"))
+
+from artdag.dag import DAG, Node, NodeType
+from artdag.engine import Engine
+from artdag import nodes  # Register executors
+
+
+def file_hash(path: Path) -> str:
+    """Compute SHA3-256 hash of a file."""
+    hasher = hashlib.sha3_256()
+    actual_path = path.resolve() if path.is_symlink() else path
+    with open(actual_path, "rb") as f:
+        for chunk in iter(lambda: f.read(65536), b""):
+            hasher.update(chunk)
+    return hasher.hexdigest()
+
+
+def main():
+    # Registry hashes (from git.rose-ash.com/art-dag/registry)
+    CAT_HASH = "33268b6e167deaf018cc538de12dbe562612b33e89a749391cef855b320a269b"
+    IDENTITY_HASH = "640ea11ee881ebf4101af0a955439105ab11e763682b209e88ea08fc66e1cc03"
+    ARTDAG_HASH = "96a5972de216aee12ec794dcad5f9360da2e676171eabf24a46dfe1ee5fee4b0"
+    WORKSTATION_HASH = "964bf6e69dc4e2493f42375013caffe26404ec3cf8eb5d9bc170cd42a361523b"
+
+    # Input
+    cat_path = Path("/home/giles/Pictures/cat.jpg")
+    output_path = Path("/home/giles/Pictures/cat-copy.jpg")
+
+    print("=== Minting cat-copy.jpg via identity-cat recipe ===\n")
+
+    # Verify input
+    input_hash = file_hash(cat_path)
+    print(f"Input: {cat_path}")
+    print(f"Input hash: {input_hash}")
+    assert input_hash == CAT_HASH, "Input hash mismatch!"
+
+    # Build DAG: SOURCE -> EFFECT(identity) -> output
+    dag = DAG(metadata={
+        "recipe": "identity-cat",
+        "recipe_url": "https://git.rose-ash.com/art-dag/recipes",
+    })
+
+    source_node = Node(
+        node_type=NodeType.SOURCE,
+        config={"path": str(cat_path)},
+        inputs=[],
+        name="source_cat",
+    )
+    source_id = dag.add_node(source_node)
+
+    effect_node = Node(
+        node_type="EFFECT",
+        config={"effect": "identity"},
+        inputs=[source_id],
+        name="apply_identity",
+    )
+    effect_id = dag.add_node(effect_node)
+
+    dag.set_output(effect_id)
+
+    # Execute through artdag engine
+    print(f"\nExecuting DAG through artdag engine...")
+    cache_dir = Path.home() / ".artdag" / "cache"
+    engine = Engine(cache_dir)
+    result = engine.execute(dag)
+
+    if not result.success:
+        print(f"FAILED: {result.error}")
+        sys.exit(1)
+
+    # Copy output to final location
+    shutil.copy2(result.output_path, output_path)
+    output_hash = file_hash(output_path)
+
+    print(f"\nOutput: {output_path}")
+    print(f"Output hash: {output_hash}")
+
+    # Verify identity property
+    assert output_hash == input_hash, "Identity property violated!"
+    print(f"\n✓ Identity property verified: output == input")
+
+    # Record provenance
+    provenance = {
+        "minted_at": datetime.now(timezone.utc).isoformat(),
+        "minted_by": "@giles@artdag.rose-ash.com",
+        "output": {
+            "name": "cat-copy",
+            "content_hash": output_hash,
+            "local_path": str(output_path),
+            "url": None,  # To be filled in after upload
+        },
+        "inputs": [
+            {"name": "cat", "content_hash": CAT_HASH}
+        ],
+        "recipe": {
+            "name": "identity-cat",
+            "url": "https://git.rose-ash.com/art-dag/recipes"
+        },
+        "effects": [
+            {"name": "effect:identity", "content_hash": IDENTITY_HASH}
+        ],
+        "infrastructure": {
+            "software": {"name": "infra:artdag", "content_hash": ARTDAG_HASH},
+            "hardware": {"name": "infra:giles-hp", "content_hash": WORKSTATION_HASH}
+        },
+        "execution": {
+            "time_seconds": result.execution_time,
+            "nodes_executed": result.nodes_executed,
+            "nodes_cached": result.nodes_cached
+        }
+    }
+
+    # Save provenance
+    provenance_path = output_path.with_suffix(".provenance.json")
+    with open(provenance_path, "w") as f:
+        json.dump(provenance, f, indent=2)
+
+    print(f"\nProvenance saved: {provenance_path}")
+    print(f"\nUpload {output_path} to rose-ash.com, then provide URL to complete minting.")
+
+    return provenance
+
+
+if __name__ == "__main__":
+    main()