Revert "Revert "feat: Add CacheProvider API for external distributed caching"" (#12915)

* Revert "Revert "feat: Add CacheProvider API for external distributed caching …"

This reverts commit d1d53c14be.

* fix: gate provider lookups to outputs cache and fix UI coercion

- Add `enable_providers` flag to BasicCache so only the outputs cache
  triggers external provider lookups/stores. The objects cache stores
  node class instances, not CacheEntry values, so provider calls were
  wasted round-trips that always missed.
- Remove `or {}` coercion on `result.ui` — an empty dict passes the
  `is not None` gate in execution.py and causes KeyError when the
  history builder indexes `["output"]` and `["meta"]`. Preserving
  `None` correctly skips the ui_node_outputs addition.

comfy_api/latest/__init__.py

@@ -25,6 +25,7 @@ class ComfyAPI_latest(ComfyAPIBase):
         super().__init__()
         self.node_replacement = self.NodeReplacement()
         self.execution = self.Execution()
+        self.caching = self.Caching()
 
     class NodeReplacement(ProxiedSingleton):
         async def register(self, node_replace: io.NodeReplace) -> None:
@@ -84,6 +85,36 @@ class ComfyAPI_latest(ComfyAPIBase):
                 image=to_display,
             )
 
+    class Caching(ProxiedSingleton):
+        """
+        External cache provider API for sharing cached node outputs
+        across ComfyUI instances.
+
+        Example::
+
+            from comfy_api.latest import Caching
+
+            class MyCacheProvider(Caching.CacheProvider):
+                async def on_lookup(self, context):
+                    ...  # check external storage
+
+                async def on_store(self, context, value):
+                    ...  # store to external storage
+
+            Caching.register_provider(MyCacheProvider())
+        """
+        from ._caching import CacheProvider, CacheContext, CacheValue
+
+        async def register_provider(self, provider: "ComfyAPI_latest.Caching.CacheProvider") -> None:
+            """Register an external cache provider. Providers are called in registration order."""
+            from comfy_execution.cache_provider import register_cache_provider
+            register_cache_provider(provider)
+
+        async def unregister_provider(self, provider: "ComfyAPI_latest.Caching.CacheProvider") -> None:
+            """Unregister a previously registered cache provider."""
+            from comfy_execution.cache_provider import unregister_cache_provider
+            unregister_cache_provider(provider)
+
 class ComfyExtension(ABC):
     async def on_load(self) -> None:
         """
@@ -116,6 +147,9 @@ class Types:
     VOXEL = VOXEL
     File3D = File3D
 
+
+Caching = ComfyAPI_latest.Caching
+
 ComfyAPI = ComfyAPI_latest
 
 # Create a synchronous version of the API
@@ -135,6 +169,7 @@ __all__ = [
     "Input",
     "InputImpl",
     "Types",
+    "Caching",
     "ComfyExtension",
     "io",
     "IO",