Fix cache file serving after cache_manager integration

- Update get_cached endpoint to check cache_manager first, then legacy
- Update get_cached_mp4 endpoint similarly
- Make cache_file() create symlink in legacy location for backward compat

Fixes issue where newly cached outputs weren't being served because
they were stored in new location but served from legacy location.

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

server.py

@@ -161,8 +161,21 @@ 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.
+    Also creates a symlink in legacy location for backward compatibility.
     """
     cached = cache_manager.put(source, node_type=node_type)
+
+    # Create symlink in legacy location for backward compatibility
+    legacy_path = CACHE_DIR / cached.content_hash
+    if not legacy_path.exists():
+        try:
+            legacy_path.symlink_to(cached.path)
+        except (OSError, FileExistsError):
+            # Symlink failed, try copy
+            import shutil
+            if not legacy_path.exists():
+                shutil.copy2(cached.path, legacy_path)
+
     return cached.content_hash
 
 
@@ -754,9 +767,16 @@ async def list_runs(request: Request, page: int = 1, limit: int = 20):
 @app.get("/cache/{content_hash}")
 async def get_cached(content_hash: str):
     """Get cached content by hash."""
-    cache_path = CACHE_DIR / content_hash
+    # Try cache_manager first (new location)
+    cache_path = cache_manager.get_by_content_hash(content_hash)
 
-    if not cache_path.exists():
+    # Fallback to legacy location
+    if not cache_path:
+        legacy_path = CACHE_DIR / content_hash
+        if legacy_path.exists():
+            cache_path = legacy_path
+
+    if not cache_path or not cache_path.exists():
         raise HTTPException(404, f"Content {content_hash} not in cache")
 
     return FileResponse(cache_path)
@@ -765,10 +785,18 @@ async def get_cached(content_hash: str):
 @app.get("/cache/{content_hash}/mp4")
 async def get_cached_mp4(content_hash: str):
     """Get cached content as MP4 (transcodes MKV on first request, caches result)."""
-    cache_path = CACHE_DIR / content_hash
+    # Try cache_manager first (new location)
+    cache_path = cache_manager.get_by_content_hash(content_hash)
+
+    # Fallback to legacy location
+    if not cache_path:
+        legacy_path = CACHE_DIR / content_hash
+        if legacy_path.exists():
+            cache_path = legacy_path
+
     mp4_path = CACHE_DIR / f"{content_hash}.mp4"
 
-    if not cache_path.exists():
+    if not cache_path or not cache_path.exists():
         raise HTTPException(404, f"Content {content_hash} not in cache")
 
     # If MP4 already cached, serve it