fix(explorer): commit the loadRangeCached/revision memoization the perf fix depends on

Repairs dev: 3ee9099 switched the Explorer call sites (and a test) to ExplorerBlockCache::loadRangeCached()
/ revision(), but those definitions were sitting uncommitted in the working tree (left over from the
explorer block-search feature, ebbeb84) and were not staged with that commit — so dev as pushed referenced
undefined members and would not compile on a clean checkout.

The infra: loadRangeCached() memoizes loadRange() per (min,max), invalidated by revision_, which is bumped
on every mutation that can change what loadRange returns (open/close/store/clear/prune/spill-reset); the
memo is capped at 16 ranges. My local builds passed only because the working tree already had these.

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

src/ui/explorer/explorer_block_cache.h

@@ -5,6 +5,7 @@
 #include <cstdint>
 #include <map>
 #include <string>
+#include <utility>
 #include <vector>
 
 struct sqlite3;
@@ -44,6 +45,11 @@ public:
     const std::string& databasePath() const { return database_path_; }
 
     std::map<int, ExplorerBlockSummary> loadRange(int minHeight, int maxHeight);
+    // loadRange memoized per (min,max) and invalidated by revision() so the per-frame Explorer list only hits SQLite
+    // after the cache actually changed (store / clear / prune / spill reset / open / close). The reference is valid
+    // until the next call; copy it if you call again before using it.
+    const std::map<int, ExplorerBlockSummary>& loadRangeCached(int minHeight, int maxHeight);
+    std::uint64_t revision() const { return revision_; }
     // Fuzzy search over cached blocks: matches when the query is a substring of the height (as text)
     // or the block hash (case-insensitive). Returns newest-first, capped at `limit`.
     std::vector<ExplorerBlockSummary> searchBlocks(const std::string& query, int limit);
@@ -102,6 +108,11 @@ private:
     int open_attempts_ = 0;
     int stores_since_prune_ = 0;
 
+    // Bumped by every mutation that can change what loadRange returns; keys the loadRangeCached memo.
+    std::uint64_t revision_ = 1;
+    std::uint64_t range_cache_revision_ = 0;
+    std::map<std::pair<int, int>, std::map<int, ExplorerBlockSummary>> range_cache_;
+
     // Blocks the DB refused, bounded and UI-thread only. Evicts the entry farthest from the last spilled height
     // (the Explorer fetches around the visible window). Cleared with clearBlocks() and when the chain tip regresses.
     static constexpr std::size_t kMaxSpillBlocks = 512;