createFilterBuilderState

Description#

Default factory behind CNGX_FILTER_BUILDER_STATE_FACTORY. Wraps one writable FilterGroup signal as the canonical tree and returns the CngxFilterBuilderState the presenter drives:

• read-only tree / fieldMap / isEmpty signals
• path-keyed mutators (addExpression, setLogic, removeNode, clear, ...)
• the lastMutation event the announcer formats into live-region text

Two-way binding: pass the presenter's model<FilterGroup>() as source, so every mutator write emits through the consumer's [(value)]. Uncontrolled callers omit source and the factory creates its own signal from initial ?? EMPTY_ROOT.

Plain TS, no inject() - testable without TestBed. Override the token to wrap this (logging, undo) rather than reimplementing the mutators.