Fix duplicated inputs on loading nested subgraphs

[AustinMroz]

Subgraphs are loaded in order of creation. Under most circumstances, this means newer subgraphs are loaded first. With nested subgraphs, this means a subgraph node has it's inputs connected before it's inside is loaded. When the inner subgraph is loaded, input-added events are triggered even though inputs already exist on the subgraph node.

This is resolved by adding a check for if an input of the corresponding name already exists when adding an input.

[christian-byrne]

Testing Recommendation

This bug highlights a gap in our test coverage for subgraph deserialization scenarios. We should add unit tests to prevent regression:

Suggested Test Cases

1. Test loading nested subgraphs with pre-existing connections

   it('should not duplicate inputs when loading nested subgraphs with existing connections', () => {
     // Create a subgraph node with inputs already connected
     // Then trigger subgraph definition loading
     // Verify no duplicate inputs are created
   })

2. Test the idempotency of input-added event handler

   it('should handle input-added events idempotently during deserialization', () => {
     // Create SubgraphNode with existing inputs
     // Manually dispatch input-added events for same inputs
     // Verify input count remains unchanged
   })

3. Test the complete serialization/deserialization cycle

   it('should correctly restore nested subgraphs without duplication', () => {
     // Create nested subgraph structure
     // Serialize to JSON
     // Deserialize and verify structure integrity
   })

These tests would help catch similar issues in the future and ensure the event system handles both runtime and loading scenarios correctly.

[christian-byrne]

This PR fixes a loading order issue where nested subgraphs loaded in creation order can cause duplicate inputs.

The problem occurs when:

• SubgraphNode has inputs connected before its inner subgraph loads
• Inner subgraph loading triggers input-added events for already-existing inputs
• The event handler adds duplicate inputs

The SubgraphNode constructor listens for input-added events:
subgraphEvents.addEventListener("input-added", (e) => {
const { name, type } = e.detail.input
this.addInput(name, type) // Runs even if input exists
})

The fix adds a guard to check for existing inputs:
if (this.inputs.find((i) => i.name == name))
return

This minimal fix preserves runtime synchronization while preventing duplication during loading. The event system was designed for runtime changes, not deserialization scenarios where state already exists.

Approved - clean fix that addresses the root cause.

[christian-byrne]

Can we change the find to some to satisfy the linter?

[AustinMroz]

Absolutely. Will look into fixing my setup so it happens automatically like it does for frontend.

[christian-byrne]

Thank you. Soon, we will merge litegraph and frontend into a single repo. Details here: Comfy-Org/ComfyUI_frontend#4667. We should make an ADR as well so all contributors are involved in the change.