feat: add BaseQueryStore for reactive query observers

src/shared/lib/helpers/BaseQueryStore.svelte.ts

@@ -0,0 +1,51 @@
+import { queryClient } from '$shared/api/queryClient';
+import {
+    QueryObserver,
+    type QueryObserverResult,
+    type QueryOptions,
+} from '@tanstack/query-core';
+
+/**
+ * Abstract base class for reactive Svelte 5 stores backed by TanStack Query.
+ *
+ * Provides a unified way to use TanStack Query observers within Svelte 5 classes
+ * using runes for reactivity. Handles subscription lifecycle automatically.
+ *
+ * @template TData - The type of data returned by the query.
+ * @template TError - The type of error that can be thrown.
+ */
+export abstract class BaseQueryStore<TData, TError = Error> {
+    #result = $state<QueryObserverResult<TData, TError>>({} as QueryObserverResult<TData, TError>);
+    #observer: QueryObserver<TData, TError>;
+    #unsubscribe: () => void;
+
+    constructor(options: QueryOptions<TData, TError, any, any, any>) {
+        this.#observer = new QueryObserver(queryClient, options);
+        this.#unsubscribe = this.#observer.subscribe(result => {
+            this.#result = result;
+        });
+    }
+
+    /**
+     * Current query result (reactive)
+     */
+    protected get result(): QueryObserverResult<TData, TError> {
+        return this.#result;
+    }
+
+    /**
+     * Updates observer options dynamically.
+     * Use this when query parameters or dependencies change.
+     */
+    protected updateOptions(options: QueryOptions<TData, TError, any, any, any>): void {
+        this.#observer.setOptions(options);
+    }
+
+    /**
+     * Cleans up the observer subscription.
+     * Should be called when the store is no longer needed.
+     */
+    destroy(): void {
+        this.#unsubscribe();
+    }
+}