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.test.ts

@@ -0,0 +1,68 @@
+import { mkdtemp, rm } from 'node:fs/promises'
+import { tmpdir } from 'node:os'
+import path from 'node:path'
+import { afterAll, describe, expect, it } from 'vitest'
+import { openGameDb, type GameDb } from '@/lib/db/client'
+import * as schema from '@/lib/db/schema'
+import { getWorldState } from './save'
+import { DEFAULT_LIMIT, EventError, MAX_LIMIT, getEvents, parseEventLimit } from './events'
+
+const dirs: string[] = []
+
+async function freshFile(): Promise<{ db: GameDb; file: string }> {
+  const dir = await mkdtemp(path.join(tmpdir(), 'sw-events-test-'))
+  dirs.push(dir)
+  const file = path.join(dir, 'test.db')
+  return { db: await openGameDb(file), file }
+}
+
+afterAll(async () => {
+  for (const d of dirs) await rm(d, { recursive: true, force: true })
+})
+
+// Appends `count` synthetic events (turns 1..count) on top of the turn-0 new_game event.
+async function seedEvents(db: GameDb, count: number): Promise<void> {
+  const [save] = await db.db.select().from(schema.saves).limit(1)
+  for (let i = 1; i <= count; i++) {
+    await db.db.insert(schema.events).values({ saveId: save.id, turn: i, type: 'test', message: `event ${i}`, createdAt: new Date(Date.UTC(2026, 8, 29, 0, i)).toISOString() })
+  }
+}
+
+describe('parseEventLimit', () => {
+  it('defaults to DEFAULT_LIMIT when the param is absent', () => {
+    expect(parseEventLimit(null)).toBe(DEFAULT_LIMIT)
+  })
+
+  it('accepts integers in [1, MAX_LIMIT]', () => {
+    expect(parseEventLimit('1')).toBe(1)
+    expect(parseEventLimit(String(MAX_LIMIT))).toBe(MAX_LIMIT)
+    expect(parseEventLimit('25')).toBe(25)
+  })
+
+  it('rejects non-integers and out-of-range values with a 400', () => {
+    for (const bad of ['abc', '', '0', '-3', String(MAX_LIMIT + 1), '2.5']) {
+      try {
+        parseEventLimit(bad)
+        expect.unreachable(`limit ${JSON.stringify(bad)} should have been rejected`)
+      } catch (err) {
+        expect(err).toBeInstanceOf(EventError)
+        expect((err as EventError).status).toBe(400)
+      }
+    }
+  })
+})
+
+describe('getEvents', () => {
+  it('returns the latest events newest-first, sliced to limit', async () => {
+    const { db } = await freshFile()
+    await getWorldState(db) // auto-initializes the save (turn-0 new_game event)
+    await seedEvents(db, 5)
+
+    const all = await getEvents(db, DEFAULT_LIMIT)
+    expect(all.map((e) => e.turn)).toEqual([5, 4, 3, 2, 1, 0]) // newest first, turn-0 line included
+    expect(all[all.length - 1].type).toBe('new_game')
+
+    const two = await getEvents(db, 2)
+    expect(two.map((e) => [e.turn, e.message])).toEqual([[5, 'event 5'], [4, 'event 4']])
+  })
+})

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 }))
+}