feat(events): event log read — getEvents + limit parsing

lib/game/events.ts: the latest N events of the save, newest first (ORDER BY
id DESC), with parseEventLimit for the optional ?limit= param (default 50,
cap 200, 400 otherwise). Unit tests cover default/accept/reject and
newest-first ordering + slicing.

lib/game/events.ts

@@ -0,0 +1,40 @@
+import { desc } from 'drizzle-orm'
+import * as schema from '@/lib/db/schema'
+import type { GameDb } from '@/lib/db/client'
+
+export interface EventDto {
+  id: number
+  turn: number
+  type: string
+  message: string
+  createdAt: string
+}
+
+export const DEFAULT_LIMIT = 50
+export const MAX_LIMIT = 200
+
+export class EventError extends Error {
+  constructor(
+    public readonly status: number,
+    message: string,
+  ) {
+    super(message)
+  }
+}
+
+// Parses the optional ?limit= query param. Absent → default; anything that is not an integer in
+// [1, MAX_LIMIT] is a 400 (the route maps EventError to its status).
+export function parseEventLimit(raw: string | null): number {
+  if (raw === null) return DEFAULT_LIMIT
+  const limit = Number(raw)
+  if (!Number.isInteger(limit) || limit < 1 || limit > MAX_LIMIT) {
+    throw new EventError(400, `limit must be an integer between 1 and ${MAX_LIMIT}`)
+  }
+  return limit
+}
+
+// The latest N events of the save, newest first. Assumes a save exists (the route calls ensureSave).
+export async function getEvents(db: GameDb, limit: number): Promise<EventDto[]> {
+  const rows = await db.db.select().from(schema.events).orderBy(desc(schema.events.id)).limit(limit)
+  return rows.map((e) => ({ id: e.id, turn: e.turn, type: e.type, message: e.message, createdAt: e.createdAt }))
+}