feat(h12): WS drop+reconnect mid-train recovery e2e

Closes V5-G08 honesty gap: V5 only added the bottom-strip
'bottom-strip-reconnecting' testid; nobody had asserted the actual
recovery path. The new scenario:

  1. Patches window.WebSocket with an init script that records every
     instance on `window.__vbgui_sockets`.
  2. Starts an N=32 Train.
  3. Calls page.evaluate to force-close every open socket → useRpc's
     onclose handler fires → backend.status="disconnected"; the 2s
     reconnect timer schedules a fresh attempt.
  4. Polls backend-status until it shows "Reconnecting/Disconnected".
  5. Polls until "Backend connected" returns (real backend stayed up;
     the reconnect succeeds on the next attempt).
  6. Asserts the pipeline.run HTTP request still completed — Train
     row in the result modal shows status "ok".

Tests:
- vbgui e2e 66_ws_reconnect.spec.ts: 1/1 passing (~3.4s).
- vbgui e2e V6 suite (55–66): 13/13 passing — no regression.

Backend WS 1Hz heartbeat (H12.7) was already in place
(cppmega_v4/jsonrpc/server.py:117), so no backend changes needed.

Author: apstenku123

vbgui/e2e/scenarios/66_ws_reconnect.spec.ts

@@ -0,0 +1,76 @@
+// H12: simulate a WS drop mid-training (via Playwright's routeWebSocket
+// to close the open ws://…/ws connection after a short delay) and
+// assert the BottomStrip transitions through reconnecting →
+// connected once the network/route recovers, while the Train
+// pipeline.run HTTP request still completes (modal shows train ok).
+// No spurious error modal should surface during the offline window —
+// the WS lives on its own reconnect timer (useRpc).
+
+import { test, expect } from "@playwright/test";
+import { gotoApp, selectPreset, closeModal } from "../fixtures";
+
+test("H12: WS drop+reconnect during Train preserves modal completion",
+  async ({ page }) => {
+    test.setTimeout(180_000);
+
+    // Wrap WebSocket so the test can close all open instances on demand.
+    // useRpc's onclose handler then fires → disconnected → 2s reconnect.
+    await page.addInitScript(() => {
+      const NativeWS = window.WebSocket;
+      const all: WebSocket[] = [];
+      (window as unknown as { __vbgui_sockets: WebSocket[] }).__vbgui_sockets
+        = all;
+      class TrackedWS extends NativeWS {
+        constructor(url: string | URL, protocols?: string | string[]) {
+          super(url, protocols);
+          all.push(this as unknown as WebSocket);
+        }
+      }
+      // @ts-expect-error - overwriting global ctor is intentional
+      window.WebSocket = TrackedWS;
+    });
+
+    await gotoApp(page);
+
+    // Wait for initial backend.status=connected.
+    await expect.poll(async () =>
+      await page.getByTestId("backend-status").textContent(),
+      { timeout: 8_000 },
+    ).toContain("Backend connected");
+
+    await selectPreset(page, "llama3_8b");
+
+    // Kick off a Train.
+    await page.getByTestId("run-pipeline-toggle").click();
+    await page.getByTestId("train-num-steps").fill("32");
+    await page.getByTestId("run-pipeline-train").click();
+    await page.waitForTimeout(200);
+
+    // Force-close every open WebSocket on the page → useRpc.onclose
+    // fires → fire("disconnected") → 2s reconnect timer.
+    await page.evaluate(() => {
+      const w = window as unknown as { __vbgui_sockets: WebSocket[] };
+      for (const s of w.__vbgui_sockets) {
+        try { s.close(); } catch { /* ignore */ }
+      }
+    });
+
+    // UI acknowledges the drop.
+    await expect.poll(async () =>
+      await page.getByTestId("backend-status").textContent(),
+      { timeout: 8_000 },
+    ).toMatch(/Reconnecting|Disconnected/);
+
+    // useRpc retries on a 2s timer → reconnects to the real backend.
+    await expect.poll(async () =>
+      await page.getByTestId("backend-status").textContent(),
+      { timeout: 15_000 },
+    ).toContain("Backend connected");
+
+    // The pipeline.run HTTP call should still complete; modal shows up.
+    await page.getByTestId("run-result-modal").waitFor({ timeout: 90_000 });
+    const trainRow = page.getByTestId("run-result-stage-train");
+    await expect(trainRow).toBeVisible();
+    await expect(trainRow).toContainText("ok");
+    await closeModal(page);
+  });