diff --git a/cache_manager.py b/cache_manager.py
new file mode 100644
index 0000000..5f4f3fa
--- /dev/null
+++ b/cache_manager.py
@@ -0,0 +1,494 @@
+# art-celery/cache_manager.py
+"""
+Cache management for Art DAG L1 server.
+
+Integrates artdag's Cache, ActivityStore, and ActivityManager to provide:
+- Content-addressed caching with both node_id and content_hash
+- Activity tracking for runs (input/output/intermediate relationships)
+- Deletion rules enforcement (shared items protected)
+- L2 ActivityPub integration for "shared" status checks
+"""
+
+import hashlib
+import json
+import logging
+import os
+import shutil
+from dataclasses import dataclass
+from datetime import datetime, timezone
+from pathlib import Path
+from typing import Callable, Dict, List, Optional, Set
+
+import requests
+
+from artdag import Cache, CacheEntry, DAG, Node, NodeType
+from artdag.activities import Activity, ActivityStore, ActivityManager, make_is_shared_fn
+
+logger = logging.getLogger(__name__)
+
+
+def file_hash(path: Path, algorithm: str = "sha3_256") -> str:
+    """Compute SHA3-256 hash of a file."""
+    hasher = hashlib.new(algorithm)
+    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()
+
+
+@dataclass
+class CachedFile:
+    """
+    A cached file with both identifiers.
+
+    Provides a unified view combining:
+    - node_id: computation identity (for DAG caching)
+    - content_hash: file content identity (for external references)
+    """
+    node_id: str
+    content_hash: str
+    path: Path
+    size_bytes: int
+    node_type: str
+    created_at: float
+
+    @classmethod
+    def from_cache_entry(cls, entry: CacheEntry) -> "CachedFile":
+        return cls(
+            node_id=entry.node_id,
+            content_hash=entry.content_hash,
+            path=entry.output_path,
+            size_bytes=entry.size_bytes,
+            node_type=entry.node_type,
+            created_at=entry.created_at,
+        )
+
+
+class L2SharedChecker:
+    """
+    Checks if content is shared (published) via L2 ActivityPub server.
+
+    Caches results to avoid repeated API calls.
+    """
+
+    def __init__(self, l2_server: str, cache_ttl: int = 300):
+        self.l2_server = l2_server
+        self.cache_ttl = cache_ttl
+        self._cache: Dict[str, tuple[bool, float]] = {}
+
+    def is_shared(self, content_hash: str) -> bool:
+        """Check if content_hash has been published to L2."""
+        import time
+        now = time.time()
+
+        # Check cache
+        if content_hash in self._cache:
+            is_shared, cached_at = self._cache[content_hash]
+            if now - cached_at < self.cache_ttl:
+                return is_shared
+
+        # Query L2
+        try:
+            resp = requests.get(
+                f"{self.l2_server}/registry/by-hash/{content_hash}",
+                timeout=5
+            )
+            is_shared = resp.status_code == 200
+        except Exception as e:
+            logger.warning(f"Failed to check L2 for {content_hash}: {e}")
+            # On error, assume not shared (safer for deletion)
+            is_shared = False
+
+        self._cache[content_hash] = (is_shared, now)
+        return is_shared
+
+    def invalidate(self, content_hash: str):
+        """Invalidate cache for a content_hash (call after publishing)."""
+        self._cache.pop(content_hash, None)
+
+    def mark_shared(self, content_hash: str):
+        """Mark as shared without querying (call after successful publish)."""
+        import time
+        self._cache[content_hash] = (True, time.time())
+
+
+class L1CacheManager:
+    """
+    Unified cache manager for Art DAG L1 server.
+
+    Combines:
+    - artdag Cache for file storage
+    - ActivityStore for run tracking
+    - ActivityManager for deletion rules
+    - L2 integration for shared status
+
+    Provides both node_id and content_hash based access.
+    """
+
+    def __init__(
+        self,
+        cache_dir: Path | str,
+        l2_server: str = "http://localhost:8200",
+    ):
+        self.cache_dir = Path(cache_dir)
+        self.cache_dir.mkdir(parents=True, exist_ok=True)
+
+        # artdag components
+        self.cache = Cache(self.cache_dir / "nodes")
+        self.activity_store = ActivityStore(self.cache_dir / "activities")
+
+        # L2 shared checker
+        self.l2_checker = L2SharedChecker(l2_server)
+
+        # Activity manager with L2-based is_shared
+        self.activity_manager = ActivityManager(
+            cache=self.cache,
+            activity_store=self.activity_store,
+            is_shared_fn=self._is_shared_by_node_id,
+        )
+
+        # Content hash index: content_hash -> node_id
+        # This enables lookup by content_hash for API compatibility
+        self._content_index: Dict[str, str] = {}
+        self._load_content_index()
+
+        # Legacy files directory (for files uploaded directly by content_hash)
+        self.legacy_dir = self.cache_dir / "legacy"
+        self.legacy_dir.mkdir(parents=True, exist_ok=True)
+
+    def _index_path(self) -> Path:
+        return self.cache_dir / "content_index.json"
+
+    def _load_content_index(self):
+        """Load content_hash -> node_id index."""
+        if self._index_path().exists():
+            try:
+                with open(self._index_path()) as f:
+                    self._content_index = json.load(f)
+            except (json.JSONDecodeError, IOError) as e:
+                logger.warning(f"Failed to load content index: {e}")
+                self._content_index = {}
+
+        # Also index from existing cache entries
+        for entry in self.cache.list_entries():
+            if entry.content_hash:
+                self._content_index[entry.content_hash] = entry.node_id
+
+    def _save_content_index(self):
+        """Save content_hash -> node_id index."""
+        with open(self._index_path(), "w") as f:
+            json.dump(self._content_index, f, indent=2)
+
+    def _is_shared_by_node_id(self, content_hash: str) -> bool:
+        """Check if a content_hash is shared via L2."""
+        return self.l2_checker.is_shared(content_hash)
+
+    # ============ File Storage ============
+
+    def put(
+        self,
+        source_path: Path,
+        node_type: str = "upload",
+        node_id: str = None,
+        execution_time: float = 0.0,
+        move: bool = False,
+    ) -> CachedFile:
+        """
+        Store a file in the cache.
+
+        Args:
+            source_path: Path to file to cache
+            node_type: Type of node (e.g., "upload", "source", "effect")
+            node_id: Optional node_id; if not provided, uses content_hash
+            execution_time: How long the operation took
+            move: If True, move instead of copy
+
+        Returns:
+            CachedFile with both node_id and content_hash
+        """
+        # Compute content hash first
+        content_hash = file_hash(source_path)
+
+        # Use content_hash as node_id if not provided
+        # This is for legacy/uploaded files that don't have a DAG node
+        if node_id is None:
+            node_id = content_hash
+
+        # Check if already cached (by node_id)
+        existing = self.cache.get_entry(node_id)
+        if existing and existing.output_path.exists():
+            return CachedFile.from_cache_entry(existing)
+
+        # Store in cache
+        self.cache.put(
+            node_id=node_id,
+            source_path=source_path,
+            node_type=node_type,
+            execution_time=execution_time,
+            move=move,
+        )
+
+        entry = self.cache.get_entry(node_id)
+
+        # Update content index
+        self._content_index[entry.content_hash] = node_id
+        self._save_content_index()
+
+        return CachedFile.from_cache_entry(entry)
+
+    def get_by_node_id(self, node_id: str) -> Optional[Path]:
+        """Get cached file path by node_id."""
+        return self.cache.get(node_id)
+
+    def get_by_content_hash(self, content_hash: str) -> Optional[Path]:
+        """Get cached file path by content_hash."""
+        # Check index first
+        node_id = self._content_index.get(content_hash)
+        if node_id:
+            path = self.cache.get(node_id)
+            if path:
+                return path
+
+        # Check legacy directory
+        legacy_path = self.legacy_dir / content_hash
+        if legacy_path.exists():
+            return legacy_path
+
+        # Scan cache entries (fallback)
+        entry = self.cache.find_by_content_hash(content_hash)
+        if entry:
+            self._content_index[content_hash] = entry.node_id
+            self._save_content_index()
+            return entry.output_path
+
+        return None
+
+    def has_content(self, content_hash: str) -> bool:
+        """Check if content exists in cache."""
+        return self.get_by_content_hash(content_hash) is not None
+
+    def get_entry_by_content_hash(self, content_hash: str) -> Optional[CacheEntry]:
+        """Get cache entry by content_hash."""
+        node_id = self._content_index.get(content_hash)
+        if node_id:
+            return self.cache.get_entry(node_id)
+        return self.cache.find_by_content_hash(content_hash)
+
+    def list_all(self) -> List[CachedFile]:
+        """List all cached files."""
+        files = []
+        for entry in self.cache.list_entries():
+            files.append(CachedFile.from_cache_entry(entry))
+
+        # Include legacy files
+        for f in self.legacy_dir.iterdir():
+            if f.is_file():
+                files.append(CachedFile(
+                    node_id=f.name,
+                    content_hash=f.name,
+                    path=f,
+                    size_bytes=f.stat().st_size,
+                    node_type="legacy",
+                    created_at=f.stat().st_mtime,
+                ))
+
+        return files
+
+    # ============ Activity Tracking ============
+
+    def record_activity(self, dag: DAG, run_id: str = None) -> Activity:
+        """
+        Record a DAG execution as an activity.
+
+        Args:
+            dag: The executed DAG
+            run_id: Optional run ID to use as activity_id
+
+        Returns:
+            The created Activity
+        """
+        activity = Activity.from_dag(dag, activity_id=run_id)
+        self.activity_store.add(activity)
+        return activity
+
+    def record_simple_activity(
+        self,
+        input_hashes: List[str],
+        output_hash: str,
+        run_id: str = None,
+    ) -> Activity:
+        """
+        Record a simple (non-DAG) execution as an activity.
+
+        For legacy single-effect runs that don't use full DAG execution.
+        Uses content_hash as node_id.
+        """
+        activity = Activity(
+            activity_id=run_id or str(hash((tuple(input_hashes), output_hash))),
+            input_ids=sorted(input_hashes),
+            output_id=output_hash,
+            intermediate_ids=[],
+            created_at=datetime.now(timezone.utc).timestamp(),
+            status="completed",
+        )
+        self.activity_store.add(activity)
+        return activity
+
+    def get_activity(self, activity_id: str) -> Optional[Activity]:
+        """Get activity by ID."""
+        return self.activity_store.get(activity_id)
+
+    def list_activities(self) -> List[Activity]:
+        """List all activities."""
+        return self.activity_store.list()
+
+    def find_activities_by_inputs(self, input_hashes: List[str]) -> List[Activity]:
+        """Find activities with matching inputs (for UI grouping)."""
+        return self.activity_store.find_by_input_ids(input_hashes)
+
+    # ============ Deletion Rules ============
+
+    def can_delete(self, content_hash: str) -> tuple[bool, str]:
+        """
+        Check if a cached item can be deleted.
+
+        Returns:
+            (can_delete, reason) tuple
+        """
+        # Check if shared via L2
+        if self.l2_checker.is_shared(content_hash):
+            return False, "Item is published to L2"
+
+        # Find node_id for this content
+        node_id = self._content_index.get(content_hash, content_hash)
+
+        # Check if it's an input or output of any activity
+        for activity in self.activity_store.list():
+            if node_id in activity.input_ids:
+                return False, f"Item is input to activity {activity.activity_id}"
+            if node_id == activity.output_id:
+                return False, f"Item is output of activity {activity.activity_id}"
+
+        return True, "OK"
+
+    def can_discard_activity(self, activity_id: str) -> tuple[bool, str]:
+        """
+        Check if an activity can be discarded.
+
+        Returns:
+            (can_discard, reason) tuple
+        """
+        activity = self.activity_store.get(activity_id)
+        if not activity:
+            return False, "Activity not found"
+
+        # Check if any item is shared
+        for node_id in activity.all_node_ids:
+            entry = self.cache.get_entry(node_id)
+            if entry and self.l2_checker.is_shared(entry.content_hash):
+                return False, f"Item {node_id} is published to L2"
+
+        return True, "OK"
+
+    def delete_by_content_hash(self, content_hash: str) -> tuple[bool, str]:
+        """
+        Delete a cached item by content_hash.
+
+        Enforces deletion rules.
+
+        Returns:
+            (success, message) tuple
+        """
+        can_delete, reason = self.can_delete(content_hash)
+        if not can_delete:
+            return False, reason
+
+        # Find and delete
+        node_id = self._content_index.get(content_hash)
+        if node_id:
+            self.cache.remove(node_id)
+            del self._content_index[content_hash]
+            self._save_content_index()
+            return True, "Deleted"
+
+        # Try legacy
+        legacy_path = self.legacy_dir / content_hash
+        if legacy_path.exists():
+            legacy_path.unlink()
+            return True, "Deleted (legacy)"
+
+        return False, "Not found"
+
+    def discard_activity(self, activity_id: str) -> tuple[bool, str]:
+        """
+        Discard an activity and clean up its cache entries.
+
+        Enforces deletion rules.
+
+        Returns:
+            (success, message) tuple
+        """
+        can_discard, reason = self.can_discard_activity(activity_id)
+        if not can_discard:
+            return False, reason
+
+        success = self.activity_manager.discard_activity(activity_id)
+        if success:
+            return True, "Activity discarded"
+        return False, "Failed to discard"
+
+    def cleanup_intermediates(self) -> int:
+        """Delete all intermediate cache entries (reconstructible)."""
+        return self.activity_manager.cleanup_intermediates()
+
+    def get_deletable_items(self) -> List[CachedFile]:
+        """Get all items that can be deleted."""
+        deletable = []
+        for entry in self.activity_manager.get_deletable_entries():
+            deletable.append(CachedFile.from_cache_entry(entry))
+        return deletable
+
+    # ============ L2 Integration ============
+
+    def mark_published(self, content_hash: str):
+        """Mark a content_hash as published to L2."""
+        self.l2_checker.mark_shared(content_hash)
+
+    def invalidate_shared_cache(self, content_hash: str):
+        """Invalidate shared status cache (call if item might be unpublished)."""
+        self.l2_checker.invalidate(content_hash)
+
+    # ============ Stats ============
+
+    def get_stats(self) -> dict:
+        """Get cache statistics."""
+        stats = self.cache.get_stats()
+        return {
+            "total_entries": stats.total_entries,
+            "total_size_bytes": stats.total_size_bytes,
+            "hits": stats.hits,
+            "misses": stats.misses,
+            "hit_rate": stats.hit_rate,
+            "activities": len(self.activity_store),
+        }
+
+
+# Singleton instance (initialized on first import with env vars)
+_manager: Optional[L1CacheManager] = None
+
+
+def get_cache_manager() -> L1CacheManager:
+    """Get the singleton cache manager instance."""
+    global _manager
+    if _manager is None:
+        cache_dir = Path(os.environ.get("CACHE_DIR", str(Path.home() / ".artdag" / "cache")))
+        l2_server = os.environ.get("L2_SERVER", "http://localhost:8200")
+        _manager = L1CacheManager(cache_dir=cache_dir, l2_server=l2_server)
+    return _manager
+
+
+def reset_cache_manager():
+    """Reset the singleton (for testing)."""
+    global _manager
+    _manager = None
diff --git a/server.py b/server.py
index 9e8729d..de3bbe1 100644
--- a/server.py
+++ b/server.py
@@ -27,6 +27,7 @@ from urllib.parse import urlparse
 
 from celery_app import app as celery_app
 from tasks import render_effect
+from cache_manager import L1CacheManager, get_cache_manager
 
 # L2 server for auth verification
 L2_SERVER = os.environ.get("L2_SERVER", "http://localhost:8200")
@@ -37,6 +38,9 @@ L1_PUBLIC_URL = os.environ.get("L1_PUBLIC_URL", "http://localhost:8100")
 CACHE_DIR = Path(os.environ.get("CACHE_DIR", str(Path.home() / ".artdag" / "cache")))
 CACHE_DIR.mkdir(parents=True, exist_ok=True)
 
+# Initialize L1 cache manager with artdag integration
+cache_manager = L1CacheManager(cache_dir=CACHE_DIR, l2_server=L2_SERVER)
+
 # Redis for persistent run storage
 REDIS_URL = os.environ.get('REDIS_URL', 'redis://localhost:6379/5')
 parsed = urlparse(REDIS_URL)
@@ -152,14 +156,14 @@ def file_hash(path: Path) -> str:
     return hasher.hexdigest()
 
 
-def cache_file(source: Path) -> str:
-    """Copy file to cache, return content hash."""
-    content_hash = file_hash(source)
-    cache_path = CACHE_DIR / content_hash
-    if not cache_path.exists():
-        import shutil
-        shutil.copy2(source, cache_path)
-    return content_hash
+def cache_file(source: Path, node_type: str = "output") -> str:
+    """
+    Copy file to cache using L1CacheManager, return content hash.
+
+    Uses artdag's Cache internally for proper tracking.
+    """
+    cached = cache_manager.put(source, node_type=node_type)
+    return cached.content_hash
 
 
 @app.get("/api")
@@ -321,7 +325,15 @@ async def get_run(run_id: str):
                 # Cache the output
                 output_path = Path(result.get("output", {}).get("local_path", ""))
                 if output_path.exists():
-                    cache_file(output_path)
+                    cache_file(output_path, node_type="effect_output")
+
+                # Record activity for deletion tracking
+                if run.output_hash and run.inputs:
+                    cache_manager.record_simple_activity(
+                        input_hashes=run.inputs,
+                        output_hash=run.output_hash,
+                        run_id=run.run_id,
+                    )
             else:
                 run.status = "failed"
                 run.error = str(task.result)
@@ -332,6 +344,42 @@ async def get_run(run_id: str):
     return run
 
 
+@app.delete("/runs/{run_id}")
+async def discard_run(run_id: str, username: str = Depends(get_required_user)):
+    """
+    Discard (delete) a run and its intermediate cache entries.
+
+    Enforces deletion rules:
+    - Cannot discard if any item (input, output) is published to L2
+    - Deletes intermediate cache entries
+    - Keeps inputs (may be used by other runs)
+    - Deletes orphaned outputs
+    """
+    run = load_run(run_id)
+    if not run:
+        raise HTTPException(404, f"Run {run_id} not found")
+
+    # Check ownership
+    actor_id = f"@{username}@{L2_DOMAIN}"
+    if run.username not in (username, actor_id):
+        raise HTTPException(403, "Access denied")
+
+    # Check if run can be discarded
+    can_discard, reason = cache_manager.can_discard_activity(run_id)
+    if not can_discard:
+        raise HTTPException(400, f"Cannot discard run: {reason}")
+
+    # Discard the activity (cleans up cache entries)
+    success, msg = cache_manager.discard_activity(run_id)
+    if not success:
+        raise HTTPException(500, f"Failed to discard: {msg}")
+
+    # Remove from Redis
+    redis_client.delete(f"{RUNS_KEY_PREFIX}{run_id}")
+
+    return {"discarded": True, "run_id": run_id}
+
+
 @app.get("/run/{run_id}")
 async def run_detail(run_id: str, request: Request):
     """Run detail. HTML for browsers, JSON for APIs."""
@@ -1428,31 +1476,45 @@ async def discard_cache(content_hash: str, username: str = Depends(get_required_
     """
     Discard (delete) a cached item.
 
-    Refuses to delete pinned items. Pinned items include:
-    - Published items
-    - Inputs to published items
+    Enforces deletion rules:
+    - Cannot delete items published to L2 (shared)
+    - Cannot delete inputs/outputs of activities (runs)
+    - Cannot delete pinned items
     """
-    cache_path = CACHE_DIR / content_hash
-    if not cache_path.exists():
-        raise HTTPException(404, "Content not found")
+    # Check if content exists (in cache_manager or legacy location)
+    if not cache_manager.has_content(content_hash):
+        cache_path = CACHE_DIR / content_hash
+        if not cache_path.exists():
+            raise HTTPException(404, "Content not found")
 
     # Check ownership
     user_hashes = get_user_cache_hashes(username)
     if content_hash not in user_hashes:
         raise HTTPException(403, "Access denied")
 
-    # Check if pinned
+    # Check if pinned (legacy metadata)
     meta = load_cache_meta(content_hash)
     if meta.get("pinned"):
         pin_reason = meta.get("pin_reason", "unknown")
         raise HTTPException(400, f"Cannot discard pinned item (reason: {pin_reason})")
 
-    # Delete the file and metadata
-    cache_path.unlink()
+    # Check deletion rules via cache_manager
+    can_delete, reason = cache_manager.can_delete(content_hash)
+    if not can_delete:
+        raise HTTPException(400, f"Cannot discard: {reason}")
+
+    # Delete via cache_manager
+    success, msg = cache_manager.delete_by_content_hash(content_hash)
+    if not success:
+        # Fallback to legacy deletion
+        cache_path = CACHE_DIR / content_hash
+        if cache_path.exists():
+            cache_path.unlink()
+
+    # Clean up legacy metadata files
     meta_path = CACHE_DIR / f"{content_hash}.meta.json"
     if meta_path.exists():
         meta_path.unlink()
-    # Also delete transcoded mp4 if exists
     mp4_path = CACHE_DIR / f"{content_hash}.mp4"
     if mp4_path.exists():
         mp4_path.unlink()
@@ -1472,18 +1534,32 @@ async def ui_discard_cache(content_hash: str, request: Request):
     if content_hash not in user_hashes:
         return '<div class="bg-red-900/50 border border-red-700 text-red-300 px-4 py-3 rounded-lg mb-4">Access denied</div>'
 
-    cache_path = CACHE_DIR / content_hash
-    if not cache_path.exists():
-        return '<div class="bg-red-900/50 border border-red-700 text-red-300 px-4 py-3 rounded-lg mb-4">Content not found</div>'
+    # Check if content exists
+    if not cache_manager.has_content(content_hash):
+        cache_path = CACHE_DIR / content_hash
+        if not cache_path.exists():
+            return '<div class="bg-red-900/50 border border-red-700 text-red-300 px-4 py-3 rounded-lg mb-4">Content not found</div>'
 
-    # Check if pinned
+    # Check if pinned (legacy metadata)
     meta = load_cache_meta(content_hash)
     if meta.get("pinned"):
         pin_reason = meta.get("pin_reason", "unknown")
         return f'<div class="bg-red-900/50 border border-red-700 text-red-300 px-4 py-3 rounded-lg mb-4">Cannot discard: item is pinned ({pin_reason})</div>'
 
-    # Delete the file and metadata
-    cache_path.unlink()
+    # Check deletion rules via cache_manager
+    can_delete, reason = cache_manager.can_delete(content_hash)
+    if not can_delete:
+        return f'<div class="bg-red-900/50 border border-red-700 text-red-300 px-4 py-3 rounded-lg mb-4">Cannot discard: {reason}</div>'
+
+    # Delete via cache_manager
+    success, msg = cache_manager.delete_by_content_hash(content_hash)
+    if not success:
+        # Fallback to legacy deletion
+        cache_path = CACHE_DIR / content_hash
+        if cache_path.exists():
+            cache_path.unlink()
+
+    # Clean up legacy metadata files
     meta_path = CACHE_DIR / f"{content_hash}.meta.json"
     if meta_path.exists():
         meta_path.unlink()
diff --git a/tests/test_cache_manager.py b/tests/test_cache_manager.py
new file mode 100644
index 0000000..76446f0
--- /dev/null
+++ b/tests/test_cache_manager.py
@@ -0,0 +1,397 @@
+# tests/test_cache_manager.py
+"""Tests for the L1 cache manager."""
+
+import tempfile
+import time
+from pathlib import Path
+from unittest.mock import Mock, patch
+
+import pytest
+
+from cache_manager import (
+    L1CacheManager,
+    L2SharedChecker,
+    CachedFile,
+    file_hash,
+)
+
+
+@pytest.fixture
+def temp_dir():
+    """Create a temporary directory for tests."""
+    with tempfile.TemporaryDirectory() as tmpdir:
+        yield Path(tmpdir)
+
+
+@pytest.fixture
+def mock_l2():
+    """Mock L2 server responses."""
+    with patch("cache_manager.requests") as mock_requests:
+        mock_requests.get.return_value = Mock(status_code=404)
+        yield mock_requests
+
+
+@pytest.fixture
+def manager(temp_dir, mock_l2):
+    """Create a cache manager instance."""
+    return L1CacheManager(
+        cache_dir=temp_dir / "cache",
+        l2_server="http://mock-l2:8200",
+    )
+
+
+def create_test_file(path: Path, content: str = "test content") -> Path:
+    """Create a test file with content."""
+    path.parent.mkdir(parents=True, exist_ok=True)
+    path.write_text(content)
+    return path
+
+
+class TestFileHash:
+    """Tests for file_hash function."""
+
+    def test_consistent_hash(self, temp_dir):
+        """Same content produces same hash."""
+        file1 = create_test_file(temp_dir / "f1.txt", "hello")
+        file2 = create_test_file(temp_dir / "f2.txt", "hello")
+
+        assert file_hash(file1) == file_hash(file2)
+
+    def test_different_content_different_hash(self, temp_dir):
+        """Different content produces different hash."""
+        file1 = create_test_file(temp_dir / "f1.txt", "hello")
+        file2 = create_test_file(temp_dir / "f2.txt", "world")
+
+        assert file_hash(file1) != file_hash(file2)
+
+    def test_sha3_256_length(self, temp_dir):
+        """Hash is SHA3-256 (64 hex chars)."""
+        f = create_test_file(temp_dir / "f.txt", "test")
+        assert len(file_hash(f)) == 64
+
+
+class TestL2SharedChecker:
+    """Tests for L2 shared status checking."""
+
+    def test_not_shared_returns_false(self, mock_l2):
+        """Non-existent content returns False."""
+        checker = L2SharedChecker("http://mock:8200")
+        mock_l2.get.return_value = Mock(status_code=404)
+
+        assert checker.is_shared("abc123") is False
+
+    def test_shared_returns_true(self, mock_l2):
+        """Published content returns True."""
+        checker = L2SharedChecker("http://mock:8200")
+        mock_l2.get.return_value = Mock(status_code=200)
+
+        assert checker.is_shared("abc123") is True
+
+    def test_caches_result(self, mock_l2):
+        """Results are cached to avoid repeated API calls."""
+        checker = L2SharedChecker("http://mock:8200", cache_ttl=60)
+        mock_l2.get.return_value = Mock(status_code=200)
+
+        checker.is_shared("abc123")
+        checker.is_shared("abc123")
+
+        # Should only call API once
+        assert mock_l2.get.call_count == 1
+
+    def test_mark_shared(self, mock_l2):
+        """mark_shared updates cache without API call."""
+        checker = L2SharedChecker("http://mock:8200")
+
+        checker.mark_shared("abc123")
+
+        assert checker.is_shared("abc123") is True
+        assert mock_l2.get.call_count == 0
+
+    def test_invalidate(self, mock_l2):
+        """invalidate clears cache for a hash."""
+        checker = L2SharedChecker("http://mock:8200")
+        mock_l2.get.return_value = Mock(status_code=200)
+
+        checker.is_shared("abc123")
+        checker.invalidate("abc123")
+
+        mock_l2.get.return_value = Mock(status_code=404)
+        assert checker.is_shared("abc123") is False
+
+    def test_error_returns_false(self, mock_l2):
+        """API errors return False (safe for deletion)."""
+        checker = L2SharedChecker("http://mock:8200")
+        mock_l2.get.side_effect = Exception("Network error")
+
+        assert checker.is_shared("abc123") is False
+
+
+class TestL1CacheManagerStorage:
+    """Tests for cache storage operations."""
+
+    def test_put_and_get_by_content_hash(self, manager, temp_dir):
+        """Can store and retrieve by content hash."""
+        test_file = create_test_file(temp_dir / "input.txt", "hello world")
+
+        cached = manager.put(test_file, node_type="test")
+
+        retrieved_path = manager.get_by_content_hash(cached.content_hash)
+        assert retrieved_path is not None
+        assert retrieved_path.read_text() == "hello world"
+
+    def test_put_with_custom_node_id(self, manager, temp_dir):
+        """Can store with custom node_id."""
+        test_file = create_test_file(temp_dir / "input.txt", "content")
+
+        cached = manager.put(test_file, node_id="custom-node-123", node_type="test")
+
+        assert cached.node_id == "custom-node-123"
+        assert manager.get_by_node_id("custom-node-123") is not None
+
+    def test_has_content(self, manager, temp_dir):
+        """has_content checks existence."""
+        test_file = create_test_file(temp_dir / "input.txt", "data")
+
+        cached = manager.put(test_file, node_type="test")
+
+        assert manager.has_content(cached.content_hash) is True
+        assert manager.has_content("nonexistent") is False
+
+    def test_list_all(self, manager, temp_dir):
+        """list_all returns all cached files."""
+        f1 = create_test_file(temp_dir / "f1.txt", "one")
+        f2 = create_test_file(temp_dir / "f2.txt", "two")
+
+        manager.put(f1, node_type="test")
+        manager.put(f2, node_type="test")
+
+        all_files = manager.list_all()
+        assert len(all_files) == 2
+
+    def test_deduplication(self, manager, temp_dir):
+        """Same content is not stored twice."""
+        f1 = create_test_file(temp_dir / "f1.txt", "identical")
+        f2 = create_test_file(temp_dir / "f2.txt", "identical")
+
+        cached1 = manager.put(f1, node_type="test")
+        cached2 = manager.put(f2, node_type="test")
+
+        assert cached1.content_hash == cached2.content_hash
+        assert len(manager.list_all()) == 1
+
+
+class TestL1CacheManagerActivities:
+    """Tests for activity tracking."""
+
+    def test_record_simple_activity(self, manager, temp_dir):
+        """Can record a simple activity."""
+        input_file = create_test_file(temp_dir / "input.txt", "input")
+        output_file = create_test_file(temp_dir / "output.txt", "output")
+
+        input_cached = manager.put(input_file, node_type="source")
+        output_cached = manager.put(output_file, node_type="effect")
+
+        activity = manager.record_simple_activity(
+            input_hashes=[input_cached.content_hash],
+            output_hash=output_cached.content_hash,
+            run_id="run-001",
+        )
+
+        assert activity.activity_id == "run-001"
+        assert input_cached.content_hash in activity.input_ids
+        assert activity.output_id == output_cached.content_hash
+
+    def test_list_activities(self, manager, temp_dir):
+        """Can list all activities."""
+        for i in range(3):
+            inp = create_test_file(temp_dir / f"in{i}.txt", f"input{i}")
+            out = create_test_file(temp_dir / f"out{i}.txt", f"output{i}")
+            inp_c = manager.put(inp, node_type="source")
+            out_c = manager.put(out, node_type="effect")
+            manager.record_simple_activity([inp_c.content_hash], out_c.content_hash)
+
+        activities = manager.list_activities()
+        assert len(activities) == 3
+
+    def test_find_activities_by_inputs(self, manager, temp_dir):
+        """Can find activities with same inputs."""
+        input_file = create_test_file(temp_dir / "shared_input.txt", "shared")
+        input_cached = manager.put(input_file, node_type="source")
+
+        # Two activities with same input
+        out1 = create_test_file(temp_dir / "out1.txt", "output1")
+        out2 = create_test_file(temp_dir / "out2.txt", "output2")
+        out1_c = manager.put(out1, node_type="effect")
+        out2_c = manager.put(out2, node_type="effect")
+
+        manager.record_simple_activity([input_cached.content_hash], out1_c.content_hash, "run1")
+        manager.record_simple_activity([input_cached.content_hash], out2_c.content_hash, "run2")
+
+        found = manager.find_activities_by_inputs([input_cached.content_hash])
+        assert len(found) == 2
+
+
+class TestL1CacheManagerDeletionRules:
+    """Tests for deletion rules enforcement."""
+
+    def test_can_delete_orphaned_item(self, manager, temp_dir):
+        """Orphaned items can be deleted."""
+        test_file = create_test_file(temp_dir / "orphan.txt", "orphan")
+        cached = manager.put(test_file, node_type="test")
+
+        can_delete, reason = manager.can_delete(cached.content_hash)
+        assert can_delete is True
+
+    def test_cannot_delete_activity_input(self, manager, temp_dir):
+        """Activity inputs cannot be deleted."""
+        input_file = create_test_file(temp_dir / "input.txt", "input")
+        output_file = create_test_file(temp_dir / "output.txt", "output")
+
+        input_cached = manager.put(input_file, node_type="source")
+        output_cached = manager.put(output_file, node_type="effect")
+
+        manager.record_simple_activity(
+            [input_cached.content_hash],
+            output_cached.content_hash,
+        )
+
+        can_delete, reason = manager.can_delete(input_cached.content_hash)
+        assert can_delete is False
+        assert "input" in reason.lower()
+
+    def test_cannot_delete_activity_output(self, manager, temp_dir):
+        """Activity outputs cannot be deleted."""
+        input_file = create_test_file(temp_dir / "input.txt", "input")
+        output_file = create_test_file(temp_dir / "output.txt", "output")
+
+        input_cached = manager.put(input_file, node_type="source")
+        output_cached = manager.put(output_file, node_type="effect")
+
+        manager.record_simple_activity(
+            [input_cached.content_hash],
+            output_cached.content_hash,
+        )
+
+        can_delete, reason = manager.can_delete(output_cached.content_hash)
+        assert can_delete is False
+        assert "output" in reason.lower()
+
+    def test_cannot_delete_shared_item(self, manager, temp_dir, mock_l2):
+        """Published items cannot be deleted."""
+        test_file = create_test_file(temp_dir / "shared.txt", "shared")
+        cached = manager.put(test_file, node_type="test")
+
+        # Mark as published
+        mock_l2.get.return_value = Mock(status_code=200)
+        manager.l2_checker.invalidate(cached.content_hash)
+
+        can_delete, reason = manager.can_delete(cached.content_hash)
+        assert can_delete is False
+        assert "L2" in reason
+
+    def test_delete_orphaned_item(self, manager, temp_dir):
+        """Can delete orphaned items."""
+        test_file = create_test_file(temp_dir / "orphan.txt", "orphan")
+        cached = manager.put(test_file, node_type="test")
+
+        success, msg = manager.delete_by_content_hash(cached.content_hash)
+
+        assert success is True
+        assert manager.has_content(cached.content_hash) is False
+
+    def test_delete_protected_item_fails(self, manager, temp_dir):
+        """Cannot delete protected items."""
+        input_file = create_test_file(temp_dir / "input.txt", "input")
+        output_file = create_test_file(temp_dir / "output.txt", "output")
+
+        input_cached = manager.put(input_file, node_type="source")
+        output_cached = manager.put(output_file, node_type="effect")
+
+        manager.record_simple_activity(
+            [input_cached.content_hash],
+            output_cached.content_hash,
+        )
+
+        success, msg = manager.delete_by_content_hash(input_cached.content_hash)
+
+        assert success is False
+        assert manager.has_content(input_cached.content_hash) is True
+
+
+class TestL1CacheManagerActivityDiscard:
+    """Tests for activity discard functionality."""
+
+    def test_can_discard_unshared_activity(self, manager, temp_dir):
+        """Activities with no shared items can be discarded."""
+        input_file = create_test_file(temp_dir / "input.txt", "input")
+        output_file = create_test_file(temp_dir / "output.txt", "output")
+
+        input_cached = manager.put(input_file, node_type="source")
+        output_cached = manager.put(output_file, node_type="effect")
+
+        activity = manager.record_simple_activity(
+            [input_cached.content_hash],
+            output_cached.content_hash,
+            "run-001",
+        )
+
+        can_discard, reason = manager.can_discard_activity("run-001")
+        assert can_discard is True
+
+    def test_cannot_discard_activity_with_shared_output(self, manager, temp_dir, mock_l2):
+        """Activities with shared outputs cannot be discarded."""
+        input_file = create_test_file(temp_dir / "input.txt", "input")
+        output_file = create_test_file(temp_dir / "output.txt", "output")
+
+        input_cached = manager.put(input_file, node_type="source")
+        output_cached = manager.put(output_file, node_type="effect")
+
+        manager.record_simple_activity(
+            [input_cached.content_hash],
+            output_cached.content_hash,
+            "run-001",
+        )
+
+        # Mark output as shared
+        manager.l2_checker.mark_shared(output_cached.content_hash)
+
+        can_discard, reason = manager.can_discard_activity("run-001")
+        assert can_discard is False
+        assert "L2" in reason
+
+    def test_discard_activity_cleans_up(self, manager, temp_dir):
+        """Discarding activity cleans up orphaned items."""
+        input_file = create_test_file(temp_dir / "input.txt", "input")
+        output_file = create_test_file(temp_dir / "output.txt", "output")
+
+        input_cached = manager.put(input_file, node_type="source")
+        output_cached = manager.put(output_file, node_type="effect")
+
+        manager.record_simple_activity(
+            [input_cached.content_hash],
+            output_cached.content_hash,
+            "run-001",
+        )
+
+        success, msg = manager.discard_activity("run-001")
+
+        assert success is True
+        assert manager.get_activity("run-001") is None
+
+
+class TestL1CacheManagerStats:
+    """Tests for cache statistics."""
+
+    def test_get_stats(self, manager, temp_dir):
+        """get_stats returns cache statistics."""
+        f1 = create_test_file(temp_dir / "f1.txt", "content1")
+        f2 = create_test_file(temp_dir / "f2.txt", "content2")
+
+        manager.put(f1, node_type="test")
+        manager.put(f2, node_type="test")
+
+        stats = manager.get_stats()
+
+        assert stats["total_entries"] == 2
+        assert stats["total_size_bytes"] > 0
+        assert "activities" in stats