feat(backend): scaffold Fastify+TS + /health

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

backend/package.json

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+{
+  "name": "thothii-backend",
+  "private": true,
+  "type": "module",
+  "scripts": {
+    "dev": "tsx watch src/server.ts",
+    "build": "tsc -p tsconfig.json",
+    "test": "vitest run",
+    "start": "node dist/server.js"
+  },
+  "dependencies": { "fastify": "^5.0.0" },
+  "devDependencies": { "typescript": "^5.6.0", "tsx": "^4.19.0", "vitest": "^2.1.0", "@types/node": "^22.0.0" }
+}

backend/src/app.ts

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+import Fastify, { type FastifyInstance } from "fastify";
+import type { AppConfig } from "./config.js";
+export function buildApp(_config: AppConfig): FastifyInstance {
+  const app = Fastify({ logger: false });
+  app.get("/health", async () => ({ status: "ok" }));
+  return app;
+}

backend/src/config.ts

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+export interface AppConfig {
+  port: number; harnessDir: string; thtBin: string; piBin: string;
+  authMode: "none" | "mock" | "oidc";
+  defaults: { provider?: string; model?: string; thinking?: string };
+  maxPiProcesses: number;
+}
+export function loadConfig(env: Record<string, string | undefined>): AppConfig {
+  return {
+    port: Number(env.PORT ?? 8787),
+    harnessDir: env.THT_HARNESS_DIR ?? "../harness",
+    thtBin: env.THT_BIN ?? "tht",
+    piBin: env.PI_BIN ?? "pi",
+    authMode: (env.AUTH_MODE as AppConfig["authMode"]) ?? "none",
+    defaults: { provider: env.PI_PROVIDER, model: env.PI_MODEL, thinking: env.PI_THINKING },
+    maxPiProcesses: Number(env.MAX_PI_PROCESSES ?? 4),
+  };
+}

backend/src/server.ts

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+import { buildApp } from "./app.js";
+import { loadConfig } from "./config.js";
+const config = loadConfig(process.env);
+const app = buildApp(config);
+app.listen({ port: config.port, host: "127.0.0.1" })
+  .then((addr) => console.log(`backend listening on ${addr}`));

backend/test/health.test.ts

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+import { test, expect } from "vitest";
+import { buildApp } from "../src/app.js";
+import { loadConfig } from "../src/config.js";
+
+test("GET /health ritorna ok", async () => {
+  const app = buildApp(loadConfig({ THT_HARNESS_DIR: "/tmp/h" }));
+  const res = await app.inject({ method: "GET", url: "/health" });
+  expect(res.statusCode).toBe(200);
+  expect(res.json()).toEqual({ status: "ok" });
+});

backend/tsconfig.json

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+{ "compilerOptions": { "target": "ES2022", "module": "ES2022", "moduleResolution": "Bundler",
+  "strict": true, "outDir": "dist", "rootDir": "src", "esModuleInterop": true, "skipLibCheck": true },
+  "include": ["src"] }

backend/vitest.config.ts

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+import { defineConfig } from "vitest/config";
+export default defineConfig({ test: { environment: "node", include: ["test/**/*.test.ts"] } });