fix(resilience,perf): gate send on a known tip, surface dropped/stale txs, advance cached confs, memoize explorer

Backlog mediums (display/gating/caching only — no send/sweep/encrypt call or args changed):

Resilience:
- Gate Send/Review on a KNOWN peer-derived tip (SyncInfo::sendTipReady): a fresh reconnect or peerless node
  has tip_known=false, so its local height isn't a trustworthy network tip — sending is disabled with a
  clear tooltip until it is. Lite is exempt (its own sync gate). The z_sendmany call is untouched.
- History now shows "Dropped" for a conflicted tx (confirmations < 0) and "Expired?" for one unconfirmed
  > 1h, instead of "Pending" forever (new TransactionInfo::isConflicted/isStalePending; the tab inlines the
  check on its DisplayTx fields).
- A cached z_viewtransaction row's confirmations now advance by the blocks mined since it was sampled
  (observed_height), instead of freezing at the cached value; never goes backwards; pending (0) isn't
  extrapolated.

Performance:
- Explorer block list uses loadRangeCached() (memoized on the cache revision) instead of loadRange(), so it
  only hits SQLite after the cache changes, not every frame.

Tests: testResilienceMediums (tip gate, confirmations-advance, dropped/stale predicates) + loadRangeCached
memoization in testExplorerBlockCache (isolated on its own cache). Held: Overview/Balance per-frame list
cache, peers clippers, off-thread tx-history cache load (larger refactors).

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

src/ui/windows/explorer_tab.cpp

@@ -846,7 +846,8 @@ static void renderRecentBlocks(App* app, float availWidth) {
 
     std::map<int, BlockSummary> cachedBlocks;
     if (!pageHeights.empty()) {
-        cachedBlocks = s_recent_block_cache.loadRange(pageHeights.back(), pageHeights.front());
+        // Memoized on the cache revision: SQLite is only hit after the cache changed, not every frame.
+        cachedBlocks = s_recent_block_cache.loadRangeCached(pageHeights.back(), pageHeights.front());
     }
 
     // Fuzzy mode: a non-numeric, non-full-hash query filters the list to cached blocks whose hash
@@ -890,7 +891,7 @@ static void renderRecentBlocks(App* app, float availWidth) {
                 }
                 std::map<int, BlockSummary> nextCachedBlocks;
                 if (!nextPageHeights.empty()) {
-                    nextCachedBlocks = s_recent_block_cache.loadRange(nextPageHeights.back(), nextPageHeights.front());
+                    nextCachedBlocks = s_recent_block_cache.loadRangeCached(nextPageHeights.back(), nextPageHeights.front());
                 }
                 for (int height : nextPageHeights) {
                     if (nextCachedBlocks.find(height) == nextCachedBlocks.end()) {

src/ui/windows/send_tab.cpp

@@ -917,7 +917,8 @@ void RenderSendConfirmPopup(App* app) {
               // since Review. Don't broadcast a now-invalid transaction.
               const auto& liveState = app->getWalletState();
               double liveAvail = GetAvailableBalance(app);
-              if (!app->isConnected() || liveState.sync.syncing || s_amount <= 0 ||
+              if (!app->isConnected() || liveState.sync.syncing ||
+                  !liveState.sync.sendTipReady(app->isLiteBuild()) || s_amount <= 0 ||
                   !util::canAfford(s_amount, s_fee, liveAvail)) {
                 s_tx_status = TR("send_cannot_send_now");
                 s_status_success = false;
@@ -1048,6 +1049,7 @@ static void RenderActionButtons(App* app, float width, float vScale,
     }
     bool can_send = app->isConnected() &&
                     !state.sync.syncing &&
+                    state.sync.sendTipReady(app->isLiteBuild()) &&
                     is_valid_address &&
                     s_amount > 0 &&
                     s_from_address[0] != '\0' &&
@@ -1072,7 +1074,7 @@ static void RenderActionButtons(App* app, float width, float vScale,
     float btnH = std::max(schema::UI().drawElement("tabs.send", "action-btn-min-height").size, schema::UI().drawElement("tabs.send", "action-btn-height").size * vScale);
 
     // Explain why Review/Send is greyed while syncing (the fields above are usable now).
-    if (state.sync.syncing) {
+    if (state.sync.syncing || (app->isConnected() && !state.sync.sendTipReady(app->isLiteBuild()))) {
         Type().textColored(TypeStyle::Caption, Warning(), TR("send_available_when_synced"));
         ImGui::Dummy(ImVec2(0, Layout::spacingXs()));
     }
@@ -1101,6 +1103,8 @@ static void RenderActionButtons(App* app, float width, float vScale,
             material::Tooltip("%s", TR(app->isLiteBuild() ? "lite_no_wallet_short" : "send_tooltip_not_connected"));
         else if (state.sync.syncing)
             material::Tooltip("%s", TR("send_tooltip_syncing"));
+        else if (!state.sync.sendTipReady(app->isLiteBuild()))
+            material::Tooltip("%s", TR("send_tooltip_no_tip"));
         else if (s_from_address[0] == '\0')
             material::Tooltip("%s", TR("send_tooltip_select_source"));
         else if (is_mining_addr)

src/ui/windows/transactions_tab.cpp

@@ -855,7 +855,12 @@ void RenderTransactionsTab(App* app)
                     {
                         const char* statusStr;
                         ImU32 statusCol;
-                        if (tx.confirmations == 0) {
+                        const int64_t nowSec = static_cast<int64_t>(std::time(nullptr));
+                        if (tx.confirmations < 0) {   // gettransaction < 0: conflicted / double-spent / reorged out
+                            statusStr = TR("tx_dropped"); statusCol = Error();
+                        } else if (tx.confirmations == 0 && tx.timestamp > 0 && nowSec - tx.timestamp > 3600) {
+                            statusStr = TR("tx_stale_pending"); statusCol = Warning();
+                        } else if (tx.confirmations == 0) {
                             statusStr = TR("pending"); statusCol = Warning();
                         } else if (tx.confirmations < 10) {
                             snprintf(buf, sizeof(buf), TR("conf_count"), tx.confirmations);