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() };
   }

frontend/src/api/sessions.ts

@@ -53,3 +53,15 @@ export const deleteSession = (id: string) =>
 
 export const getSessionDocuments = (id: string) =>
   apiFetch<SessionDocument[]>(`/sessions/${id}/documents`);
+
+export async function checkDwhHealth(): Promise<{ ok: boolean }> {
+  const timeout = new Promise<{ ok: false }>((r) => setTimeout(() => r({ ok: false }), 5000));
+  try {
+    return await Promise.race([
+      apiFetch<{ ok: boolean; detail: string }>("/health/dwh"),
+      timeout,
+    ]);
+  } catch {
+    return { ok: false };
+  }
+}

frontend/src/shell/AppShell.new-session.test.tsx

@@ -100,7 +100,7 @@ test("a DWH-unreachable precheck shows a specific alert and preserves the questi
     http.post("http://localhost:8787/sessions", () =>
       HttpResponse.json(
         {
-          error: "Cannot start a session: the data warehouse is unreachable. Check the VPN connection and try again.",
+          error: "Cannot start a session: the database is unreachable. Check the VPN connection and try again.",
           code: "dwh_unreachable",
         },
         { status: 503 },
@@ -113,7 +113,7 @@ test("a DWH-unreachable precheck shows a specific alert and preserves the questi
   await userEvent.click(screen.getByRole("button", { name: /send/i }));
 
   // Specific alert, not the generic "failed to create session" hint.
-  expect(await screen.findByText(/data warehouse is unreachable/i)).toBeInTheDocument();
+  expect(await screen.findByText(/database is unreachable/i)).toBeInTheDocument();
   expect(screen.queryByText(/failed to create session/i)).not.toBeInTheDocument();
   // No session was created: landing view stays and the question is kept for retry.
   expect(screen.getByText(/type your question/i)).toBeInTheDocument();

frontend/src/shell/AppShell.tsx

@@ -20,7 +20,11 @@ import { toast } from "sonner";
 import {
   closeSession, getMe, listSessions, resumeSession, getSession,
   renameSession, setSessionGroup, archiveSession, unarchiveSession, deleteSession, prewarmRuntime,
+  checkDwhHealth,
 } from "../api/sessions";
+import {
+  Dialog, DialogContent, DialogDescription, DialogFooter, DialogHeader, DialogTitle,
+} from "../components/ui/dialog";
 import type { Principal, SessionScope, SessionSummary } from "../api/types";
 import { useQuery, useQueryClient } from "@tanstack/react-query";
 import { useEffect, useMemo, useRef, useState } from "react";
@@ -89,6 +93,19 @@ export function AppShell() {
   const [stopConfirm, setStopConfirm] = useState(false);
   const [collapsedGroups, setCollapsedGroups] = useState<Record<string, boolean>>({});
   const [renameGroupTarget, setRenameGroupTarget] = useState<string | null>(null);
+  const [dwhDown, setDwhDown] = useState(false);
+  const [dwhChecking, setDwhChecking] = useState(true);
+  const [dwhCheckEpoch, setDwhCheckEpoch] = useState(0);
+  useEffect(() => {
+    let cancelled = false;
+    setDwhChecking(true);
+    checkDwhHealth().then((r) => {
+      if (cancelled) return;
+      setDwhDown(!r.ok);
+      setDwhChecking(false);
+    });
+    return () => { cancelled = true; };
+  }, [dwhCheckEpoch]);
 
   const groups = useMemo(
     () => [...new Set(sessions.map((s) => s.group).filter((g): g is string => !!g))].sort(),
@@ -759,6 +776,26 @@ export function AppShell() {
           }}
         />
       )}
+      {dwhDown && (
+        <Dialog open onOpenChange={() => {}}>
+          <DialogContent showCloseButton={false} className="sm:max-w-md">
+            <DialogHeader>
+              <DialogTitle>Connection unavailable</DialogTitle>
+              <DialogDescription>
+                The database is unreachable. Check the VPN connection and try again.
+              </DialogDescription>
+            </DialogHeader>
+            <DialogFooter>
+              <Button
+                disabled={dwhChecking}
+                onClick={() => setDwhCheckEpoch((e) => e + 1)}
+              >
+                {dwhChecking ? "Checking…" : "Retry"}
+              </Button>
+            </DialogFooter>
+          </DialogContent>
+        </Dialog>
+      )}
     </div>
   );
 }
@@ -770,7 +807,7 @@ function EmptyState() {
         Thoth<span className="text-primary">II</span>
       </span>
       <p className="mt-4 max-w-md text-balance text-[0.95rem] leading-relaxed text-muted-foreground">
-        Build datamarts from your data warehouse through a guided,
+        Build datamarts from your database through a guided,
         human-in-the-loop workflow. Type your question in the box below to begin
         a session.
       </p>

frontend/src/test/msw.ts

@@ -1,2 +1,5 @@
 import { setupServer } from "msw/node";
-export const server = setupServer();
+import { http, HttpResponse } from "msw";
+export const server = setupServer(
+  http.get("http://localhost:8787/health/dwh", () => HttpResponse.json({ ok: true, detail: "ok" })),
+);