feat: complete remaining Go backend modules

tests/assets-http-contract.test.ts

@@ -0,0 +1,21 @@
+import { readFile } from "node:fs/promises";
+import { describe, expect, it } from "vitest";
+
+describe("assets HTTP v1 compatibility contract", () => {
+  it("freezes route, limit, safe-error, and binary-cache semantics", async () => {
+    const contract = JSON.parse(await readFile(new URL("../contracts/assets/http-v1.json", import.meta.url), "utf8"));
+    expect(contract.version).toBe(1);
+    expect(contract.limits).toEqual({ jsonBytes: 1_048_576, uploadBytes: 20_971_520, remoteBytes: 20_971_520 });
+    expect(contract.routes.map((route: { path: string }) => route.path)).toEqual([
+      "/api/assets", "/api/assets/upload", "/api/assets/{id}", "/api/assets/{id}/download",
+      "/api/v1/assets", "/api/v1/assets/{id}", "/api/v1/assets/{id}/download",
+      "/uploads/{path...}", "/generated-results/{path...}"
+    ]);
+    expect(contract.errors.internal.body).toEqual({ error: "Internal server error." });
+    expect(contract.methods).toEqual({ headExecutesGet: true, optionsStatus: 204, unsupportedStatus: 405, unsupportedBody: "empty" });
+    expect(contract.binary).toEqual({
+      downloadCacheControl: "private, no-store",
+      servedCacheControl: "public, max-age=31536000, immutable"
+    });
+  });
+});