chore: dev-stack switches, shared e2e harness, and desktop shell rules

- `LIVE_RELOAD=false npm run dev` keeps the renderer alive across a machine
  suspend; the reload client otherwise destroys the session under test.
- `dev-peer.sh` plus a separate userdata dir runs a second local peer.
- `tools/voice-probe.js` samples peer state and RTP counters from a live
  window, persisting to localStorage so a renderer reload cannot erase it.
- e2e helpers for voice pairs, peer-role election, and a TURN relay.
- Electron single-instance and dev-client-load decisions move into rules
  files with colocated specs.

electron/window/dev-client-load.rules.ts

@@ -0,0 +1,49 @@
+export const DEV_CLIENT_LOAD_ATTEMPTS = 10;
+export const DEV_CLIENT_RETRY_DELAY_MS = 500;
+
+export type DevClientLoadOutcome = 'loaded' | 'aborted' | 'failed';
+
+export interface DevClientLoadDeps {
+  load: () => Promise<void>;
+  isAborted: () => boolean;
+  wait: (delayMs: number) => Promise<void>;
+  onRetry: (attempt: number, error: unknown) => void;
+  onGiveUp: (attempts: number, error: unknown) => void;
+}
+
+/**
+ * The dev client is served by a watch-mode build, so a load can fail for
+ * reasons that resolve on their own: a rebuild in flight, or a shutdown that
+ * aborted the navigation. Failing hard skipped every window listener
+ * registered after the load and left a blank window with no message, so this
+ * retries and always reports instead of throwing.
+ */
+export async function loadDevelopmentClientWithRetry(deps: DevClientLoadDeps): Promise<DevClientLoadOutcome> {
+  for (let attempt = 1; attempt <= DEV_CLIENT_LOAD_ATTEMPTS; attempt += 1) {
+    if (deps.isAborted()) {
+      return 'aborted';
+    }
+
+    try {
+      await deps.load();
+
+      return 'loaded';
+    } catch (error) {
+      if (deps.isAborted()) {
+        return 'aborted';
+      }
+
+      if (attempt === DEV_CLIENT_LOAD_ATTEMPTS) {
+        deps.onGiveUp(attempt, error);
+
+        return 'failed';
+      }
+
+      deps.onRetry(attempt, error);
+
+      await deps.wait(DEV_CLIENT_RETRY_DELAY_MS);
+    }
+  }
+
+  return 'failed';
+}