feat(fullnode): auto-reconcile wallet after bootstrap; runtime rescan for pruned nodes

A wallet bootstrapped from a snapshot keeps its wallet.dat but never rescans, so
its spent-state is stale and the first send tries to spend already-spent notes and
is rejected. The startup -rescan flag can't fix it either: the snapshot lacks the
pre-snapshot block history -rescan needs, so it errors. The working fix is a runtime
rescanblockchain RPC from a height the snapshot actually has.

- Add App::runtimeRescan(startHeight): runs rescanblockchain via the worker, drives
  the rescanning UI state, and owns completion via the RPC callback (getrescaninfo
  is unavailable on this daemon). Suppresses the per-second mining/rescan pollers
  and the Core/balance/tx refreshes while the daemon holds cs_main for the scan.
- Add App::detectLowestAvailableBlockHeight(): async binary search via getblock for
  the lowest height whose block data is on disk → the snapshot base, and whether the
  node still has full history.
- Auto-reconcile after bootstrap: both completion sites (wizard + Settings download
  dialog) mark a pending rescan; once the daemon is back up and the tip is known,
  detect the base and runtimeRescan() from it (or -rescan restart on a full node).
- Settings "Rescan Blockchain" now probes first: full-history nodes get the existing
  -rescan restart; bootstrapped/pruned nodes get a prompt pre-filled with the
  detected base height that runs the runtime rescan.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

src/app.h

@@ -305,7 +305,19 @@ public:
     bool isEmbeddedDaemonRunning() const;
     bool isUsingEmbeddedDaemon() const { return supportsEmbeddedDaemon() && use_embedded_daemon_; }
     void setUseEmbeddedDaemon(bool use) { use_embedded_daemon_ = use && supportsEmbeddedDaemon(); }
-    void rescanBlockchain();  // restart daemon with -rescan flag
+    void rescanBlockchain();  // restart daemon with -rescan flag (full-history nodes)
+    // Runtime rescanblockchain RPC starting at a snapshot-available height. Unlike the
+    // -rescan restart, this works on bootstrapped/pruned nodes (which lack pre-snapshot
+    // block data), reconciling the wallet's stale spent-state without a daemon restart.
+    void runtimeRescan(int startHeight);
+    // Async binary-search probe for the lowest block height the node still has on disk.
+    // cb(ok, lowestHeight, fullHistory): fullHistory==true when genesis is present (a normal,
+    // non-bootstrapped node). Runs on the UI thread via the RPC worker callbacks.
+    void detectLowestAvailableBlockHeight(std::function<void(bool ok, int lowestHeight, bool fullHistory)> cb);
+    // Flag that a bootstrap just finished so the wallet auto-reconciles spent-state once the
+    // daemon is back up (consumed in update()).
+    void markPostBootstrapRescanPending() { post_bootstrap_rescan_pending_ = true; }
+    bool runtimeRescanActive() const { return runtime_rescan_active_; }
     void repairWallet();  // restart daemon with -zapwallettxes=2 (wipe & rebuild wallet tx records)
     void reinstallBundledDaemon();  // stop daemon, overwrite installed binary with the bundled one, restart
     void deleteBlockchainData();  // stop daemon, delete chain data, restart fresh
@@ -616,6 +628,13 @@ private:
     // Gates the "rescan complete" detection so a getrescaninfo poll that hits the still-running
     // pre-restart daemon (which reports rescanning=false) can't fire a false "complete" instantly.
     bool rescan_confirmed_active_ = false;
+    // A runtime rescanblockchain RPC is in flight (vs the -rescan daemon restart). While set,
+    // the per-second mining/rescan-status pollers are suppressed (the daemon holds cs_main for
+    // the whole scan and would block them); completion is signalled by the rescan RPC callback.
+    bool runtime_rescan_active_ = false;
+    // Set when a bootstrap completes; consumed once the daemon is connected to auto-run a rescan
+    // that reconciles the preserved wallet.dat against the freshly-imported chain.
+    bool post_bootstrap_rescan_pending_ = false;
     bool opid_poll_in_progress_ = false;
     // Consecutive Core-refresh cycles where BOTH core RPCs failed → likely a dead
     // connection. After kCoreFailuresBeforeDisconnect, tear down and reconnect.