For Loops don't work in latest ComfyUI in --cache-none mode

[wallentri88]

Custom Node Testing

• I have tried disabling custom nodes and the issue persists (see how to disable custom nodes if you need help)

Expected Behavior

For Loops work in --cache-none mode

Actual Behavior

Traceback (most recent call last):
  File "/home/.../ComfyUI/execution.py", line 548, in execute
    subcache = await cache.ensure_subcache_for(unique_id, new_node_ids)
               ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/home/.../ComfyUI/comfy_execution/caching.py", line 423, in ensure_subcache_for
    self.ancestors[child_id].add(node_id)
    ~~~~~~~~~~~~~~^^^^^^^^^^
KeyError: '4.0.0.1'```

I tried to replace it on `setdefault`, but got index out of range error in other place

### Steps to Reproduce

Use any custom nodes which implement For Loops, for example from here, using this workflow (embedded): https://github.com/BadCafeCode/execution-inversion-demo-comfyui/blob/main/examples/SimpleForLoop.png

### Debug Logs

```powershell
!!! Exception during processing !!!

Other

using comfyui commit 4ffea0e

[HelloClyde]

I recently discovered a bug in cache-none as well, and I'm not sure if it's related to your issue.

The comfyui cache-none uses DependencyAwareCache, but the associated hash method is CacheKeySetInputSignature. This means that if two nodes have the same inputs, they actually share the same cached entry—for example, Node 1 and Node 2 both point to the same cache slot.

However, when DependencyAwareCache detects that Node 1 has no further dependencies, it removes the corresponding cache entry, which unfortunately also deletes the cache that Node 2 relies on.

You can fix this by modifying the relevant code in execution.py.

    # only hold cached items while the decendents have not executed
    def init_dependency_aware_cache(self):
        self.outputs = DependencyAwareCache(CacheKeySetInputSignature)
        self.ui = DependencyAwareCache(CacheKeySetInputSignature)
        self.objects = DependencyAwareCache(CacheKeySetID)

to

    # only hold cached items while the decendents have not executed
    def init_dependency_aware_cache(self):
        self.outputs = DependencyAwareCache(CacheKeySetID)
        self.ui = DependencyAwareCache(CacheKeySetID)
        self.objects = DependencyAwareCache(CacheKeySetID)

Additional note: After reviewing the code again, I found that the issue is caused by an incomplete implementation of the method DependencyAwareCache.ensure_subcache_for.
This problem can be fixed with a simple patch:

    async def ensure_subcache_for(self, node_id, children_ids):
        """
        Ensure a subcache exists for a node and update dependencies.

        Args:
            node_id: The ID of the parent node.
            children_ids: List of child node IDs to associate with the parent node.

        Returns:
            The subcache object for the node.
        """
        subcache = await super()._ensure_subcache(node_id, children_ids)
        await self.cache_key_set.add_keys(children_ids)
        for child_id in children_ids:
            self.descendants[node_id].add(child_id)
            if child_id not in self.ancestors:
                self.ancestors[child_id] = set()
            self.ancestors[child_id].add(node_id)
        return subcache

[Kosinkadink]

@wallentri88 the issue should now be fixed, let me know if all is good on your end now!