desloppify: code health overhaul plus abuse hardening (140 green, strict 87.2)

Honest baseline after removing 45 gaming suppressions. Structural: lib/game plus root hooks extraction, CORS origin echo, DEV_ORIGINS layering. Fixes: error-cause binding, discord 5xx split, null-cache guard, co-located tests, rejecting-fetch coverage, naming and typing cleanup, socket controller, cache bound, cascade helpers, latch resets. Hardening: per-IP rate limit on API routes, deterministic-miss UX, retry cooldown plus cap. Suite 140 green, build plus lint clean.

app/api/discord-app/[id]/route.ts

@@ -1,37 +1,32 @@
-import { NextResponse } from "next/server";
-import { corsHeaders, forbidden, isAllowedOrigin } from "@/lib/api-cors";
-import { getDiscordAppInfo } from "@/lib/lanyard";
+import { getDiscordAppInfo } from "@/lib/game/discord-app";
+import {
+    invalidIdResponse,
+    jsonErrorWithCors,
+    jsonWithCors,
+    parseAppId,
+    requestOrigin,
+} from "@/lib/api-route";
+import { warnDev } from "@/lib/log";
+import type { NextResponse } from "next/server";
 
-export async function OPTIONS(request: Request) {
-    if (!isAllowedOrigin(request)) {
-        return forbidden();
+export async function GET(
+    request: Request,
+    context: { params: Promise<{ id: string }> },
+): Promise<NextResponse> {
+    const origin = requestOrigin(request);
+    const id = await parseAppId(context);
+    if (!id) {
+        return invalidIdResponse(origin);
     }
-    return new NextResponse(null, {
-        status: 204,
-        headers: {
-            ...corsHeaders(),
-            "Access-Control-Allow-Methods": "GET, OPTIONS",
-            "Access-Control-Max-Age": "86400",
-        },
-    });
-}
-
-export async function GET(request: Request, context: { params: Promise<{ id: string }> }) {
-    if (!isAllowedOrigin(request)) {
-        return forbidden();
+    let info;
+    try {
+        info = await getDiscordAppInfo(id);
+    } catch (error) {
+        warnDev(`discord-app upstream failed: ${id} -> ${error instanceof Error ? error.message : error}`);
+        return jsonErrorWithCors({ error: "Upstream unavailable" }, 502, 60, origin);
     }
-    const { id } = await context.params;
-    if (!/^\d+$/.test(id)) {
-        return NextResponse.json({ error: "Invalid application id" }, { status: 400 });
-    }
-    const info = await getDiscordAppInfo(id);
     if (!info) {
-        return NextResponse.json({ error: "Application not found" }, { status: 404 });
+        return jsonErrorWithCors({ error: "Application not found" }, 404, 60, origin);
     }
-    return NextResponse.json(info, {
-        headers: {
-            "Cache-Control": "public, s-maxage=86400, stale-while-revalidate=86400",
-            ...corsHeaders(),
-        },
-    });
+    return jsonWithCors(info, 86400, origin);
 }