fix(bindx): support direct field access on PlaceholderHandle proxy (#7)

PlaceholderHandle.wrapProxy used createAliasProxy which only strips the
$ prefix but does not delegate unknown properties to target.fields.
This caused entity.fieldName to return undefined for placeholder
entities (e.g. when creating new entities via HasOne).

Switch to createHandleProxy so that direct field access (entity.name)
resolves through the fields proxy, matching EntityHandle behavior.

Also transition disconnected relations to 'creating' state when
SET_PLACEHOLDER_DATA is dispatched, ensuring placeholder data is
properly tracked for new entities.

Author: vparys

packages/bindx/src/core/ActionDispatcher.ts

@@ -265,11 +265,15 @@ export class ActionDispatcher {
 					action.fieldPath,
 					action.value,
 				)
+				// When setting placeholder data on a disconnected relation, transition to 'creating'
+				const stateUpdate = (!relation || relation.state === 'disconnected')
+					? { state: 'creating' as const, placeholderData: newPlaceholderData }
+					: { placeholderData: newPlaceholderData }
 				this.store.setRelation(
 					action.entityType,
 					action.entityId,
 					action.fieldName,
-					{ placeholderData: newPlaceholderData },
+					stateUpdate,
 				)
 				break
 			}

packages/bindx/src/handles/PlaceholderHandle.ts

@@ -18,7 +18,7 @@ import type {
 	EntityPersistedEvent,
 	EntityPersistingEvent,
 } from '../events/types.js'
-import { createAliasProxy } from './proxyFactory.js'
+import { createHandleProxy } from './proxyFactory.js'
 import type { SchemaRegistry } from '../schema/SchemaRegistry.js'
 
 /**
@@ -77,7 +77,7 @@ export class PlaceholderHandle<TEntity extends object = object, TSelected = TEnt
 	}
 
 	static wrapProxy<TEntity extends object, TSelected>(handle: PlaceholderHandle<TEntity, TSelected>): EntityAccessor<TEntity, TSelected> {
-		return createAliasProxy<PlaceholderHandle<TEntity, TSelected>, EntityAccessor<TEntity, TSelected>>(handle)
+		return createHandleProxy<PlaceholderHandle<TEntity, TSelected>, EntityAccessor<TEntity, TSelected>>(handle, (target) => target.fields)
 	}
 
 	/**