ui/phase-12: order composer skeleton

OrderDraftStore persists per-game command drafts in Cache; the
sidebar Order tab renders the list with a per-row delete control.
The layout passes a `historyMode` prop through Sidebar / BottomTabs
as a constant `false`, so Phase 26 only flips the source.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

ui/frontend/src/sync/order-draft.svelte.ts

@@ -0,0 +1,125 @@
+// Per-game runes store that owns the local order draft. Mirrors the
+// Phase 11 `GameStateStore` lifecycle: one instance per game, created
+// in `routes/games/[id]/+layout.svelte`, exposed to descendants via
+// Svelte context, disposed when the layout unmounts.
+//
+// Draft state is persisted into the platform `Cache` under the
+// `order-drafts` namespace with a per-game key, so a reload, a
+// browser restart, or a navigation through the lobby and back into
+// the same game restores the previously composed list. Phase 14
+// will add the submit pipeline that drains the draft to the server;
+// Phase 26 will hide the order tab in history mode through a flag
+// passed by the layout (the store itself remains alive across that
+// transition so the draft survives history-mode round-trips).
+//
+// The store deliberately carries no Svelte component imports so it
+// can be tested directly with a synthetic `Cache` without rendering
+// any UI.
+
+import type { Cache } from "../platform/store/index";
+import type { OrderCommand } from "./order-types";
+
+const NAMESPACE = "order-drafts";
+const draftKey = (gameId: string): string => `${gameId}/draft`;
+
+/**
+ * ORDER_DRAFT_CONTEXT_KEY is the Svelte context key the in-game shell
+ * layout uses to expose its `OrderDraftStore` instance to descendants.
+ * The order tab and any later command-builder UI resolve the store via
+ * `getContext(ORDER_DRAFT_CONTEXT_KEY)`.
+ */
+export const ORDER_DRAFT_CONTEXT_KEY = Symbol("order-draft");
+
+type Status = "idle" | "ready" | "error";
+
+export class OrderDraftStore {
+	commands: OrderCommand[] = $state([]);
+	status: Status = $state("idle");
+	error: string | null = $state(null);
+
+	private cache: Cache | null = null;
+	private gameId = "";
+	private destroyed = false;
+
+	/**
+	 * init loads the persisted draft for `opts.gameId` from `opts.cache`
+	 * into `commands` and flips `status` to `ready`. The call is
+	 * idempotent on the same store instance — the layout always
+	 * constructs a fresh store per game, so there is no need to support
+	 * mid-life game switching here.
+	 */
+	async init(opts: { cache: Cache; gameId: string }): Promise<void> {
+		this.cache = opts.cache;
+		this.gameId = opts.gameId;
+		try {
+			const stored = await opts.cache.get<OrderCommand[]>(
+				NAMESPACE,
+				draftKey(opts.gameId),
+			);
+			if (this.destroyed) return;
+			this.commands = Array.isArray(stored) ? [...stored] : [];
+			this.status = "ready";
+		} catch (err) {
+			if (this.destroyed) return;
+			this.status = "error";
+			this.error = err instanceof Error ? err.message : "load failed";
+		}
+	}
+
+	/**
+	 * add appends a command to the end of the draft and persists the
+	 * updated list. Mutations made before `init` resolves are ignored —
+	 * the layout always awaits `init` before exposing the store.
+	 */
+	async add(command: OrderCommand): Promise<void> {
+		if (this.status !== "ready") return;
+		this.commands = [...this.commands, command];
+		await this.persist();
+	}
+
+	/**
+	 * remove drops the command with the given id from the draft and
+	 * persists the result. A miss is a no-op.
+	 */
+	async remove(id: string): Promise<void> {
+		if (this.status !== "ready") return;
+		const next = this.commands.filter((cmd) => cmd.id !== id);
+		if (next.length === this.commands.length) return;
+		this.commands = next;
+		await this.persist();
+	}
+
+	/**
+	 * move relocates the command at `fromIndex` to `toIndex`, shifting
+	 * the intermediate commands. Out-of-range indices and identical
+	 * positions are no-ops; both indices are clamped against the
+	 * current `commands` length.
+	 */
+	async move(fromIndex: number, toIndex: number): Promise<void> {
+		if (this.status !== "ready") return;
+		const length = this.commands.length;
+		if (fromIndex < 0 || fromIndex >= length) return;
+		if (toIndex < 0 || toIndex >= length) return;
+		if (fromIndex === toIndex) return;
+		const next = [...this.commands];
+		const [picked] = next.splice(fromIndex, 1);
+		if (picked === undefined) return;
+		next.splice(toIndex, 0, picked);
+		this.commands = next;
+		await this.persist();
+	}
+
+	dispose(): void {
+		this.destroyed = true;
+		this.cache = null;
+	}
+
+	private async persist(): Promise<void> {
+		if (this.cache === null || this.destroyed) return;
+		// `commands` is `$state`, so individual entries are proxies.
+		// IndexedDB's structured clone refuses to clone proxies, so the
+		// snapshot must be taken before the put.
+		const snapshot = $state.snapshot(this.commands) as OrderCommand[];
+		await this.cache.put(NAMESPACE, draftKey(this.gameId), snapshot);
+	}
+}