feat: initial recipes repo with identity-cat

- Recipe schema using artdag primitives (SOURCE, EFFECT)
- identity-cat: applies identity effect to cat image
- Test verifying identity property: output_hash == input_hash
- Demonstrates content-addressed DAG execution

Owner: @giles@artdag.rose-ash.com

🤖 Generated with [Claude Code](https://claude.com/claude-code)

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

.gitignore

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+__pycache__/
+*.py[cod]
+.env
+.venv

README.md

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+# Art DAG Recipes
+
+Recipes that transform assets using effects from [art-dag](https://github.com/gilesbradshaw/art-dag).
+
+## Structure
+
+```
+recipes/
+└── identity-cat/
+    ├── recipe.yaml    # DAG definition
+    └── README.md      # Description
+```
+
+## Registry References
+
+Recipes reference assets and effects by content hash from:
+- **Assets**: https://github.com/gilesbradshaw/art-dag/blob/main/registry/registry.json
+- **Effects**: https://github.com/gilesbradshaw/art-dag/tree/main/effects
+
+## Recipe Schema
+
+A recipe is a DAG with:
+- `name`: Unique recipe identifier
+- `inputs`: Assets referenced by content_hash
+- `nodes`: DAG nodes using primitives (SOURCE, TRANSFORM, etc.) and effects
+- `output`: Expected output hash (for verification)
+
+## Owner
+
+Recipes owned by `@giles@artdag.rose-ash.com`

recipes/identity-cat/README.md

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+# identity-cat
+
+The simplest possible recipe: apply the identity effect to the foundational cat image.
+
+## DAG
+
+```
+┌─────────────┐     ┌────────────────┐     ┌────────────┐
+│ SOURCE(cat) │ ──▶ │ EFFECT(identity)│ ──▶ │   output   │
+└─────────────┘     └────────────────┘     └────────────┘
+     33268b...           passthrough            33268b...
+```
+
+## Properties
+
+Since `identity(x) = x`:
+- Input hash: `33268b6e167deaf018cc538de12dbe562612b33e89a749391cef855b320a269b`
+- Output hash: `33268b6e167deaf018cc538de12dbe562612b33e89a749391cef855b320a269b`
+
+The hashes are identical, proving the identity property.
+
+## References
+
+- **Asset**: [cat](https://rose-ash.com/content/images/2026/01/cat.jpg)
+- **Effect**: [identity](https://github.com/gilesbradshaw/art-dag/tree/main/effects/identity)
+
+## Owner
+
+`@giles@artdag.rose-ash.com`

recipes/identity-cat/recipe.yaml

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+# identity-cat recipe
+# Applies the identity effect to the foundational cat image
+# Demonstrates: SOURCE → EFFECT → output
+
+name: identity-cat
+version: "1.0"
+description: "Apply identity effect to cat - output equals input"
+
+# Registry references (by content hash)
+registry:
+  assets:
+    cat:
+      hash: "33268b6e167deaf018cc538de12dbe562612b33e89a749391cef855b320a269b"
+      url: "https://rose-ash.com/content/images/2026/01/cat.jpg"
+  effects:
+    identity:
+      hash: "640ea11ee881ebf4101af0a955439105ab11e763682b209e88ea08fc66e1cc03"
+      url: "https://github.com/gilesbradshaw/art-dag/tree/main/effects/identity"
+
+# DAG definition
+dag:
+  nodes:
+    - id: source_cat
+      type: SOURCE
+      config:
+        asset: cat
+
+    - id: apply_identity
+      type: EFFECT
+      config:
+        effect: identity
+      inputs:
+        - source_cat
+
+  output: apply_identity
+
+# Verification
+output:
+  # Identity property: output hash equals input hash
+  expected_hash: "33268b6e167deaf018cc538de12dbe562612b33e89a749391cef855b320a269b"
+
+# Ownership
+owner: "@giles@artdag.rose-ash.com"

test_identity_cat.py

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+#!/usr/bin/env python3
+"""
+Test the identity-cat recipe.
+
+Verifies that identity(cat) produces the same content hash as cat.
+"""
+
+import hashlib
+import sys
+import tempfile
+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()
+    # Resolve symlinks to get actual content
+    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():
+    # Cat image location (from registry)
+    cat_url = "https://rose-ash.com/content/images/2026/01/cat.jpg"
+    cat_hash = "33268b6e167deaf018cc538de12dbe562612b33e89a749391cef855b320a269b"
+
+    # Try to find cat locally
+    cat_paths = [
+        Path("/home/giles/Pictures/cat.jpg"),
+        Path.home() / "Pictures" / "cat.jpg",
+    ]
+
+    cat_path = None
+    for p in cat_paths:
+        if p.exists():
+            cat_path = p
+            break
+
+    if not cat_path:
+        print(f"Cat image not found locally. Download from: {cat_url}")
+        sys.exit(1)
+
+    # Verify input hash
+    input_hash = file_hash(cat_path)
+    print(f"Input: {cat_path}")
+    print(f"Input hash: {input_hash}")
+
+    if input_hash != cat_hash:
+        print(f"WARNING: Input hash doesn't match registry!")
+        print(f"Expected: {cat_hash}")
+
+    # Build the DAG: SOURCE -> EFFECT(identity) -> output
+    dag = DAG()
+
+    # Node 1: SOURCE(cat)
+    source_node = Node(
+        node_type=NodeType.SOURCE,
+        config={"path": str(cat_path)},
+        inputs=[],
+        name="source_cat",
+    )
+    source_id = dag.add_node(source_node)
+
+    # Node 2: EFFECT(identity)
+    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
+    with tempfile.TemporaryDirectory() as cache_dir:
+        engine = Engine(cache_dir)
+        result = engine.execute(dag)
+
+        if not result.success:
+            print(f"FAILED: {result.error}")
+            sys.exit(1)
+
+        # Verify output hash
+        output_hash = file_hash(result.output_path)
+        print(f"\nOutput: {result.output_path}")
+        print(f"Output hash: {output_hash}")
+
+        # The identity property: output hash == input hash
+        if output_hash == input_hash:
+            print("\n✓ PASS: identity(cat) == cat")
+            print("  Output hash equals input hash - identity property verified!")
+        else:
+            print("\n✗ FAIL: identity(cat) != cat")
+            print(f"  Expected: {input_hash}")
+            print(f"  Got:      {output_hash}")
+            sys.exit(1)
+
+
+if __name__ == "__main__":
+    main()