Feature request: Change source/origin tracking in onChange

[AleksY1991]

Use case:
Building custom sync logic with Supabase Realtime. Need to distinguish:

• User changes → sync to database
• Realtime changes → update local state, skip re-sync to avoid loops

Current workaround:
Module-scoped flags checked in onChange:
let isRemote = false;

store$.nodes.onChange(({ changes }) => {
if (isRemote) return; // skip sync
syncToDatabase(changes);
});

// Realtime handler:
isRemote = true;
store$.nodes[id].set(data);
isRemote = false;

Problems:

• Flags are module-scoped, not composable
• Any code can write to observables without setting flags
• No enforcement, purely convention-based

Proposed solution:
Optional source or context parameter on writes that flows through to onChange:

store$.nodes[id].set(data, { source: 'remote' });

store$.nodes.onChange(({ changes, source }) => {
if (source === 'remote') return;
syncToDatabase(changes);
});