Fix relay E2EE reconnect races (#973)

* Fix relay E2EE reconnect races

* fix(relay): use WebSocket protocol ping for daemon control keepalive

The daemon's control socket pinged the relay every 10s with a JSON
`{type:"ping"}` message. Every JSON message wakes a hibernated Cloudflare
Durable Object via `webSocketMessage`, so an idle daemon was billing
relay DO CPU 24/7 just to echo `pong`.

Switch to `socket.ping()` (RFC 6455 protocol ping frames). Cloudflare's
runtime auto-responds at the edge without waking hibernated DOs, so an
idle daemon-to-relay connection now costs zero DO CPU.

Liveness still works: the `ws` library emits a `pong` event on the
daemon when the edge replies, which refreshes `controlLastSeenAt`.
`markControlReady` stays tied to DO-originated messages (sync,
connected, disconnected), so we still detect a broken DO at connect.

The DO keeps its JSON ping handler tagged `COMPAT(relay-json-ping)` so
old daemons (< v0.1.76) continue to work.

* test(relay): assert protocol-ping pongs arrive in e2e idle test

Adds a `relay_control_pong_received` debug log to the daemon's pong
handler, then asserts in the existing idle-relay e2e test that:

  - at least one pong arrived during the 12s idle wait (proving the
    Cloudflare edge auto-responds to RFC 6455 protocol pings)
  - no stale terminations fired (proving the keepalive path is healthy)

If the daemon ever regresses to JSON-level keepalive pings (which wake
the hibernated relay Durable Object and incur CPU billing), this test
will catch it: the `pong` event would never fire because the DO's reply
would arrive via `message`, not as a protocol pong frame.

The test's capturing logger is bumped to `debug` level so the assertion
can read the new debug log; production daemons stay at `info`.

Confirmed locally against wrangler-hosted relay: 2 pongs / 0 stale per
12s window.

* test(relay): catch dual-ping regression via DO-side legacy ping log

The existing idle-test assertion catches "revert to JSON ping only" via
the missing pong event, but misses the dual-ping regression where
someone adds `socket.send(JSON.stringify({type:"ping"}))` alongside
`socket.ping()`. Both paths would work, the pong assertion still
passes, and DO CPU billing silently returns.

Add a console.log in the DO's handleControlKeepalive (which only runs
when a JSON ping reaches the DO), then assert in the idle e2e test
that no such log appeared during the 12s idle window.

Verified the assertion catches the regression: temporarily injected a
`socket.send(JSON.stringify({type:"ping"}))` next to socket.ping(),
test failed with `expected 1 to be 0` and the relay logged
`legacy_json_ping_received`. Removed the injection.

Log noise during the COMPAT window doubles as useful telemetry: it
counts how many old daemons are still pinging, which informs the
removal date for the COMPAT shim.

packages/app/src/runtime/host-runtime.test.ts

@@ -302,6 +302,58 @@ function makeProbeMap(
 }
 
 describe("HostRuntimeController", () => {
+  it("replaces the active relay client when re-pairing changes the daemon public key", async () => {
+    const oldRelay: HostConnection = {
+      id: "relay:wss:relay.paseo.sh:443",
+      type: "relay",
+      relayEndpoint: "relay.paseo.sh:443",
+      useTls: true,
+      daemonPublicKeyB64: "pk_old",
+    };
+    const newRelay: HostConnection = {
+      ...oldRelay,
+      daemonPublicKeyB64: "pk_new",
+    };
+    const createdClients: Array<{ client: FakeDaemonClient; connection: HostConnection }> = [];
+    const controller = new HostRuntimeController({
+      host: makeHost({
+        connections: [oldRelay],
+        preferredConnectionId: oldRelay.id,
+      }),
+      deps: {
+        createClient: ({ connection }) => {
+          const client = new FakeDaemonClient();
+          createdClients.push({ client, connection });
+          return client as unknown as DaemonClient;
+        },
+        connectToDaemon: async ({ host, connection }) => ({
+          client: makeConnectedProbeClient(5) as unknown as DaemonClient,
+          serverId: host.serverId,
+          hostname: connection.id,
+        }),
+        getClientId: async () => "cid_test_runtime",
+      },
+    });
+
+    await (
+      controller as unknown as {
+        switchToConnection: (input: { connectionId: string }) => Promise<void>;
+      }
+    ).switchToConnection({ connectionId: oldRelay.id });
+    expect(controller.getSnapshot().client).toBe(createdClients[0]?.client);
+
+    await controller.updateHost(
+      makeHost({
+        connections: [newRelay],
+        preferredConnectionId: newRelay.id,
+      }),
+    );
+
+    expect(createdClients.map((entry) => entry.connection)).toEqual([oldRelay, newRelay]);
+    expect(createdClients[0]?.client.closeCalls).toBe(1);
+    expect(controller.getSnapshot().client).toBe(createdClients[1]?.client);
+  });
+
   it("keeps known hosts in connecting when a created client reports idle during connect", async () => {
     const host = makeHost({
       connections: [