de: Simplify serialization

[aMayzner]

Node graph serialization in Data Explorer previously required every node type to manually include connection IDs in its serializeState() (e.g. leftNodeId, primaryInputId, unionNodes) and a corresponding deserializeConnections hook to restore them. This was error-prone and meant adding a new node type required remembering to handle connections in multiple places.

Connections are now captured automatically at the graph level in serializeNode() and restored generically in deserializeState(). Node serializeState() methods only need to handle their own configuration data.

Backward compatibility with old saved graphs (where connection IDs lived inside node state) is handled by a single declarative lookup table in legacy_connections.ts, keeping it out of core_nodes.ts entirely.

[github-actions]

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• 9e7d782 (2026-03-30 15:20 UTC): https://storage.googleapis.com/perfetto-ci-artifacts/gh-23752372495-1-ui/ui/index.html