There is no way to observe cell ID changes via public API

[krassowski]

Description

The public API does not expose ymodel nor propagate the cell ID changes.

jupyter_ydoc/javascript/src/ycell.ts

Lines 367 to 369 in 7234533

	getId(): string {
	return this.ymodel.get('id');
	}

jupyter_ydoc/javascript/src/ycell.ts

Line 190 in 7234533

this.ymodel.observeDeep(this._modelObserver);

jupyter_ydoc/javascript/src/ycell.ts

Lines 570 to 625 in 7234533

	protected getChanges(events: Y.YEvent<any>[]): Partial<CellChange> {
	const changes: CellChange = {};
	const sourceEvent = events.find(
	event => event.target === this.ymodel.get('source')
	);
	if (sourceEvent) {
	changes.sourceChange = sourceEvent.changes.delta as any;
	}
	const metadataEvents = events.find(
	event => event.target === this._ymetadata
	);
	if (metadataEvents) {
	changes.metadataChange = metadataEvents.changes.keys;
	metadataEvents.changes.keys.forEach((change, key) => {
	switch (change.action) {
	case 'add':
	this._metadataChanged.emit({
	key,
	newValue: this._ymetadata.get(key),
	type: 'add'
	});
	break;
	case 'delete':
	this._metadataChanged.emit({
	key,
	oldValue: change.oldValue,
	type: 'remove'
	});
	break;
	case 'update':
	{
	const newValue = this._ymetadata.get(key);
	const oldValue = change.oldValue;
	let equal = true;
	if (typeof oldValue == 'object' && typeof newValue == 'object') {
	equal = JSONExt.deepEqual(oldValue, newValue);
	} else {
	equal = oldValue === newValue;
	}
	if (!equal) {
	this._metadataChanged.emit({
	key,
	type: 'change',
	oldValue,
	newValue
	});
	}
	}
	break;
	}
	});
	}

There is also no way to listen to cell_type changes. If we assume that either or both are immutable then we should document it.

This came up in jupyterlab/jupyterlab#18101.