feat: add GachaEvent schema and stable event IDs

Schema-level invariants enforce that endsAt is null exactly when
endPrecision is "unknown", and that regionEnds is populated exactly when
regionScoped is set, so an event object cannot be constructed in a state
the UI would misrender.

Event IDs double as localStorage keys on the client, so slugify() and
eventId() carry a warning: changing them orphans every user's completion
marks with no server-side recovery.

Co-Authored-By: Claude Opus 5 (1M context) <[email protected]>

src/shared/schema.ts

@@ -0,0 +1,106 @@
+import { z } from "zod";
+
+export const GameId = z.enum([
+  "genshin",
+  "hsr",
+  "zzz",
+  "wuwa",
+  "arknights",
+  "endfield",
+  "nte", // Neverness to Everness
+]);
+export type GameId = z.infer<typeof GameId>;
+
+export const EventType = z.enum([
+  "banner", // limited character/weapon rate-up
+  "story", // main or side story chapter, limited-time
+  "rerun", // returning event
+  "challenge", // combat/endgame cycle (Abyss, Onslaught, Trial, ...)
+  "login", // login rewards / check-in
+  "shop", // limited shop or exchange window
+  "maintenance", // server downtime
+  "other",
+]);
+export type EventType = z.infer<typeof EventType>;
+
+export const Region = z.enum(["asia", "america", "europe"]);
+export type Region = z.infer<typeof Region>;
+
+/**
+ * How much we actually know about a boundary timestamp.
+ * - "exact"   sourced to the minute
+ * - "day"     date known, time-of-day not stated by the source
+ * - "unknown" not announced; the paired timestamp is null
+ */
+export const Precision = z.enum(["exact", "day", "unknown"]);
+export type Precision = z.infer<typeof Precision>;
+
+export const GachaEvent = z
+  .object({
+    id: z.string(),
+    game: GameId,
+    title: z.string().min(1).max(200),
+    type: EventType,
+    summary: z.string().max(500).nullable(),
+
+    startsAt: z.string().datetime(),
+    startPrecision: Precision,
+    endsAt: z.string().datetime().nullable(),
+    endPrecision: Precision,
+
+    regionScoped: z.boolean(),
+    regionEnds: z.record(Region, z.string().datetime()).nullable(),
+
+    sourceUrl: z.string().url(),
+    sourceId: z.string(),
+
+    status: z.enum(["published", "delisted"]),
+    confidence: z.number().min(0).max(1),
+    extractionMethod: z.enum(["parser", "manual"]),
+
+    version: z.number().int().positive(),
+    firstSeenAt: z.string().datetime(),
+    updatedAt: z.string().datetime(),
+  })
+  // These invariants are cheap here and prevent a whole class of wrong-date bugs
+  // reaching the feed. See docs/INGESTION.md § Stage 4.
+  .refine((e) => (e.endsAt === null) === (e.endPrecision === "unknown"), {
+    message: "endsAt null must pair with endPrecision 'unknown'",
+    path: ["endPrecision"],
+  })
+  .refine((e) => (e.regionEnds === null) === !e.regionScoped, {
+    message: "regionEnds must be populated exactly when regionScoped is true",
+    path: ["regionEnds"],
+  })
+  .refine((e) => e.endsAt === null || e.endsAt > e.startsAt, {
+    message: "endsAt must be after startsAt",
+    path: ["endsAt"],
+  });
+
+export type GachaEvent = z.infer<typeof GachaEvent>;
+
+/**
+ * Stable, deterministic event ID.
+ *
+ * WARNING: these are localStorage keys on the client. Changing this function —
+ * including the slug rules — orphans every completion mark every user has, with
+ * no server-side recovery. See docs/DATA-MODEL.md § ID stability.
+ */
+export function slugify(input: string): string {
+  return input
+    .normalize("NFKD")
+    .replace(/[̀-ͯ]/g, "")
+    .toLowerCase()
+    .replace(/['‘’]/g, "")
+    .replace(/[^a-z0-9]+/g, "-")
+    .replace(/^-+|-+$/g, "")
+    .slice(0, 80);
+}
+
+export function eventId(
+  game: GameId,
+  title: string,
+  startsAt: string,
+): string {
+  return `${game}:${slugify(title)}:${startsAt.slice(0, 10)}`;
+}