fix: prevent duplicate edges between same nodes

[yasir-ali9]

Description

Fixes an issue where users could create multiple edges between the same two nodes, causing duplicate connections in the workflow data.

Problem

Users could drag from a node handle multiple times to create duplicate edges between the same source and target nodes. This created redundant data and visual clutter in the workflow canvas.

Example of the issue:

"edges": [
  {"id": "edge1", "source": "nodeA", "target": "nodeB"},
  {"id": "edge2", "source": "nodeA", "target": "nodeB"},  // Duplicate
  {"id": "edge3", "source": "nodeA", "target": "nodeB"}   // Duplicate
]

Solution

Added duplicate edge prevention in the onConnect and handleConnectionToNewNode functions in workflow-canvas.tsx:

Check for existing edges between the same source and target before creating new ones
Early return if a duplicate edge already exists
Maintains existing UX while preventing data integrity issues

[vercel]

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