feat(core): add error feature (#713)

packages/store/src/core/selector.ts

@@ -7,6 +7,7 @@ import type { AnySlice, InferSliceState, StateContext } from './slice';
 const stateContext: StateContext<unknown> = {
   target: throwNoTargetError,
   signals: new AbortControllerRegistry(),
+  set: throwNoTargetError,
 };
 
 /**

packages/store/src/core/slice.ts

@@ -40,6 +40,8 @@ export interface StateContext<Target> {
    *   (e.g., loading a new source cancels pending seeks).
    */
   signals: AbortControllerRegistry;
+  /** Patch the slice state. Safe to use inside action closures (not during `state()` init). */
+  set: (partial: Record<string, unknown>) => void;
 }
 
 // ----------------------------------------

packages/store/src/core/store.ts

@@ -38,6 +38,7 @@ export function createStore<Target = unknown>(): <State>(
         return target!;
       },
       signals,
+      set: (partial) => state.patch(partial as Partial<State>),
     } satisfies StateContext<Target>);
 
     state = createState(initialState);