feat: DWH connectivity probe at startup — modal alert within 5s if unreachable

Backend: GET /health/dwh (unauthenticated) calls tht db ping with a 5s
timeout. Frontend: checkDwhHealth() races a 5s timer against the fetch;
on failure a non-dismissable Dialog with Retry appears immediately.

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

backend/src/app.ts

@@ -86,10 +86,11 @@ export function buildApp(config: AppConfig, deps?: BuildAppDeps): FastifyInstanc
   const authenticate = authPreHandler(config.authMode);
   app.addHook("preHandler", async (req, reply) => {
     // Process readiness is intentionally unauthenticated for local container/proxy probes.
-    if (req.url === "/health") return;
+    if (req.url === "/health" || req.url === "/health/dwh") return;
     return authenticate(req, reply);
   });
   app.get("/health", async () => ({ status: "ok" }));
+  app.get("/health/dwh", async () => tht.dbPing());
   app.get("/me", async (req) => getPrincipal(req));
   sessionRoutes(app, {
     mgr, tht: tht as ThtRunner, hub, getSettings, readiness, dwhPrecheck: config.dwhPrecheck,

backend/src/routes/sessions.ts

@@ -14,7 +14,7 @@ const READINESS_FAILURE_MESSAGE =
 const RESUME_FAILURE_MESSAGE =
   "Session could not be resumed. Check configuration and connectivity, then try again.";
 const DWH_UNREACHABLE_MESSAGE =
-  "Cannot start a session: the data warehouse is unreachable. Check the VPN connection and try again.";
+  "Cannot start a session: the database is unreachable. Check the VPN connection and try again.";
 
 export function sessionRoutes(
   app: FastifyInstance,

backend/src/tht/tht-runner.ts

@@ -154,7 +154,7 @@ export class ThtRunner {
    * cleanly. Timed out to keep POST /sessions responsive when the host hangs.
    */
   async dbPing(workspace?: string): Promise<{ ok: boolean; detail: string }> {
-    const { code, stdout, stderr } = await this.run(["db", "ping"], workspace, 10_000);
+    const { code, stdout, stderr } = await this.run(["db", "ping"], workspace, 5_000);
     if (code === 0) return { ok: true, detail: stdout.trim() };
     return { ok: false, detail: (stderr || stdout).trim() };
   }