feat: distributed rendering with Celery

- celery_app.py: Celery configuration with Redis broker
- tasks.py: render_effect task with full provenance tracking
- render.py: CLI for submitting render jobs
- Successfully renders cat → dog with provenance chain

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

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

tasks.py

@@ -0,0 +1,151 @@
+"""
+Art DAG Celery Tasks
+
+Distributed rendering tasks for the Art DAG system.
+"""
+
+import hashlib
+import json
+import sys
+from datetime import datetime, timezone
+from pathlib import Path
+
+from celery import Task
+from celery_app import app
+
+# Add effects to path
+EFFECTS_PATH = Path.home() / "artdag-effects"
+sys.path.insert(0, str(EFFECTS_PATH / "dog"))
+
+
+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()
+
+
+class RenderTask(Task):
+    """Base task with provenance tracking."""
+
+    def on_success(self, retval, task_id, args, kwargs):
+        """Record successful render."""
+        print(f"Task {task_id} completed: {retval}")
+
+    def on_failure(self, exc, task_id, args, kwargs, einfo):
+        """Record failed render."""
+        print(f"Task {task_id} failed: {exc}")
+
+
+@app.task(base=RenderTask, bind=True)
+def render_effect(self, input_hash: str, effect_name: str, output_name: str) -> dict:
+    """
+    Render an effect on an input asset.
+
+    Args:
+        input_hash: SHA3-256 hash of input asset
+        effect_name: Name of effect (e.g., "dog", "identity")
+        output_name: Name for output asset
+
+    Returns:
+        Provenance record with output hash
+    """
+    # Registry hashes
+    REGISTRY = {
+        "cat": {
+            "hash": "33268b6e167deaf018cc538de12dbe562612b33e89a749391cef855b320a269b",
+            "path": Path.home() / "artdag-art" / "cat.jpg"
+        },
+        "effect:dog": {
+            "hash": "d048fe313433eb4e38f0e24194ffae91b896ca3e6eed3e50b2cc37b7be495555"
+        },
+        "effect:identity": {
+            "hash": "640ea11ee881ebf4101af0a955439105ab11e763682b209e88ea08fc66e1cc03"
+        },
+        "infra:artdag": {
+            "hash": "96a5972de216aee12ec794dcad5f9360da2e676171eabf24a46dfe1ee5fee4b0"
+        },
+        "infra:giles-hp": {
+            "hash": "964bf6e69dc4e2493f42375013caffe26404ec3cf8eb5d9bc170cd42a361523b"
+        }
+    }
+
+    # Find input by hash
+    input_asset = None
+    input_name = None
+    for name, data in REGISTRY.items():
+        if data.get("hash") == input_hash and "path" in data:
+            input_asset = data
+            input_name = name
+            break
+
+    if not input_asset:
+        raise ValueError(f"Unknown input hash: {input_hash}")
+
+    input_path = input_asset["path"]
+    output_dir = Path.home() / "artdag-art"
+
+    # Verify input
+    actual_hash = file_hash(input_path)
+    if actual_hash != input_hash:
+        raise ValueError(f"Input hash mismatch: expected {input_hash}, got {actual_hash}")
+
+    self.update_state(state='RENDERING', meta={'effect': effect_name, 'input': input_name})
+
+    # Load and apply effect
+    if effect_name == "dog":
+        from effect import effect_dog, DOG_HASH
+        output_path = output_dir / f"{output_name}.mkv"
+        result = effect_dog(input_path, output_path, {})
+        expected_hash = DOG_HASH
+    elif effect_name == "identity":
+        from artdag.nodes.effect import effect_identity
+        output_path = output_dir / f"{output_name}{input_path.suffix}"
+        result = effect_identity(input_path, output_path, {})
+        expected_hash = input_hash
+    else:
+        raise ValueError(f"Unknown effect: {effect_name}")
+
+    # Verify output
+    output_hash = file_hash(result)
+    if output_hash != expected_hash:
+        raise ValueError(f"Output hash mismatch: expected {expected_hash}, got {output_hash}")
+
+    # Build provenance
+    provenance = {
+        "task_id": self.request.id,
+        "rendered_at": datetime.now(timezone.utc).isoformat(),
+        "rendered_by": "@giles@artdag.rose-ash.com",
+        "output": {
+            "name": output_name,
+            "content_hash": output_hash,
+            "local_path": str(result)
+        },
+        "inputs": [
+            {"name": input_name, "content_hash": input_hash}
+        ],
+        "effects": [
+            {"name": f"effect:{effect_name}", "content_hash": REGISTRY[f"effect:{effect_name}"]["hash"]}
+        ],
+        "infrastructure": {
+            "software": {"name": "infra:artdag", "content_hash": REGISTRY["infra:artdag"]["hash"]},
+            "hardware": {"name": "infra:giles-hp", "content_hash": REGISTRY["infra:giles-hp"]["hash"]}
+        }
+    }
+
+    # Save provenance
+    provenance_path = result.with_suffix(".provenance.json")
+    with open(provenance_path, "w") as f:
+        json.dump(provenance, f, indent=2)
+
+    return provenance
+
+
+@app.task
+def render_dog_from_cat() -> dict:
+    """Convenience task: render cat through dog effect."""
+    CAT_HASH = "33268b6e167deaf018cc538de12dbe562612b33e89a749391cef855b320a269b"
+    return render_effect.delay(CAT_HASH, "dog", "dog-from-cat-celery").get()