fix(rpc): drop a stale connect result after teardown; don't let open() erase a pending abort

Concurrency audit, connect-lifecycle races (no fund-path call touched — connect-result gating + abort-flag
lifetime only):
- The connect task's MainCb ran onConnected() on any successful probe without re-checking that a wallet
  switch / adopt / restore / shutdown had already torn the connection down — so a probe that succeeded
  against the old daemon could start a refresh against one about to be stopped. Capture rpc_session_ when
  posting (main thread) and, in the MainCb, drop the result (requestAbort + disconnect, not a blocking bare
  disconnect) when the session changed or daemon_restarting_/shutting_down_ is set. Same guard on the
  cookie-auth retry post.
- RPCClient::open() called clearAbort(), so a requestAbort() issued while a connect was still queued was
  erased, stalling teardown/shutdown. open() no longer clears it; the two reconnect entry points
  (tryConnect for rpc_, onConnected for fast_rpc_) clear it on the main thread first, skipped while
  shutting_down_ so a shutdown abort survives. A fresh client defaults to not-aborted, so first connects
  are unaffected.

HELD (not in this commit): making abortMaintenanceCalls() abort unconditionally (the UI-freeze-on-disconnect
finding) — it would also abort an in-flight user send during teardown, a send-lifecycle behaviour change
that wants explicit sign-off (it is fund-safe via the lost-reply "outcome unknown" handling, but still a
behaviour change).

Threading fix — clean build + ctest; the races are runtime-only.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

src/rpc/rpc_client.cpp

@@ -216,7 +216,8 @@ bool RPCClient::open(const std::string& host, const std::string& port,
     curl_easy_setopt(impl_->curl, CURLOPT_HTTPHEADER, impl_->headers);
     curl_easy_setopt(impl_->curl, CURLOPT_WRITEFUNCTION, WriteCallback);
     // Progress callback so requestAbort() can unblock an in-flight curl_easy_perform.
-    clearAbort();  // a fresh connection must not start in the aborted state
+    // NOTE: abort is deliberately NOT cleared here: a requestAbort() issued while this connect was queued
+    // must still cut it short. Reconnect callers (App::tryConnect / onConnected) call clearAbort() first.
     curl_easy_setopt(impl_->curl, CURLOPT_NOPROGRESS, 0L);
     curl_easy_setopt(impl_->curl, CURLOPT_XFERINFOFUNCTION, xferInfoCallback);
     curl_easy_setopt(impl_->curl, CURLOPT_XFERINFODATA, this);