feat(isolation): process isolation for custom nodes via pyisolate

Adds opt-in process isolation for custom nodes using pyisolate's
bwrap sandbox and JSON-RPC bridge. Each isolated node pack runs in
its own child process with zero-copy tensor transfer via shared memory.

Core infrastructure:
- CLI flag --use-process-isolation to enable isolation
- Host/child startup fencing via PYISOLATE_CHILD env var
- Manifest-driven node discovery and extension loading
- JSON-RPC bridge between host and child processes
- Shared memory forensics for leak detection

Proxy layer:
- ModelPatcher, CLIP, VAE, and ModelSampling proxies
- Host service proxies (folder_paths, model_management, progress, etc.)
- Proxy base with automatic method forwarding

Execution integration:
- Extension wrapper with V3 hidden param mapping
- Runtime helpers for isolated node execution
- Host policy for node isolation decisions
- Fenced sampler device handling and model ejection parity

Serializers for cross-process data transfer:
- File3D (GLB), PLY (structured + gaussian), NPZ (streaming frames),
  VIDEO (VideoFromFile + VideoFromComponents) serializers
- data_type flag in SerializerRegistry for type-aware dispatch
- Isolated get_temp_directory() fence

New core save nodes:
- SavePLY and SaveNPZ with comfytype registrations (Ply, Npz)

DynamicVRAM compatibility:
- comfy-aimdo early init gated by isolation fence

Tests:
- Integration and policy tests for isolation lifecycle
- Manifest loader, host policy, proxy, and adapter unit tests

Depends on: pyisolate >= 0.9.2

tests/test_adapter.py

@@ -0,0 +1,51 @@
+import os
+import sys
+from pathlib import Path
+
+repo_root = Path(__file__).resolve().parents[1]
+pyisolate_root = repo_root.parent / "pyisolate"
+if pyisolate_root.exists():
+    sys.path.insert(0, str(pyisolate_root))
+
+from comfy.isolation.adapter import ComfyUIAdapter
+from pyisolate._internal.serialization_registry import SerializerRegistry
+
+
+def test_identifier():
+    adapter = ComfyUIAdapter()
+    assert adapter.identifier == "comfyui"
+
+
+def test_get_path_config_valid():
+    adapter = ComfyUIAdapter()
+    path = os.path.join("/opt", "ComfyUI", "custom_nodes", "demo")
+    cfg = adapter.get_path_config(path)
+    assert cfg is not None
+    assert cfg["preferred_root"].endswith("ComfyUI")
+    assert "custom_nodes" in cfg["additional_paths"][0]
+
+
+def test_get_path_config_invalid():
+    adapter = ComfyUIAdapter()
+    assert adapter.get_path_config("/random/path") is None
+
+
+def test_provide_rpc_services():
+    adapter = ComfyUIAdapter()
+    services = adapter.provide_rpc_services()
+    names = {s.__name__ for s in services}
+    assert "PromptServerService" in names
+    assert "FolderPathsProxy" in names
+
+
+def test_register_serializers():
+    adapter = ComfyUIAdapter()
+    registry = SerializerRegistry.get_instance()
+    registry.clear()
+
+    adapter.register_serializers(registry)
+    assert registry.has_handler("ModelPatcher")
+    assert registry.has_handler("CLIP")
+    assert registry.has_handler("VAE")
+
+    registry.clear()