* [bugfix] Fix widget disconnection issue in subgraphs
When disconnecting a node from a SubgraphInput, the target input's link
reference was not being cleared in LLink.disconnect(). This caused
widgets to remain greyed out because they still thought they were
connected (slot.link was not null).
The fix ensures that when a link is disconnected, the target node's
input slot is properly cleaned up by setting input.link = null.
Fixes#4922🤖 Generated with [Claude Code](https://claude.ai/code)
* [test] Add tests for LLink disconnect fix for widget issue
Add comprehensive tests for the LLink.disconnect() method to verify
that target input link references are properly cleared when disconnecting.
This prevents widgets from remaining greyed out after disconnection.
Tests cover:
- Basic disconnect functionality with link reference cleanup
- Edge cases with invalid target nodes
- Preventing interference between different connections
Related to #4922🤖 Generated with [Claude Code](https://claude.ai/code)
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Co-authored-by: Christian Byrne <cbyrne@comfy.org>
Co-authored-by: Claude <noreply@anthropic.com>
