utxosnapshot: gate requireCheckpoint on trust source

Local file snapshots (init.cpp) skip the known-checkpoint gate; P2P-delivered
snapshots (bootstrap.cpp) keep it. Rationale: the checkpoint gate exists to
prevent malicious peers from injecting fake UTXO sets. Local file loads come
from operator-trusted sources (filesystem access already grants equal power),
so the gate is unnecessary friction.

src/bootstrap.cpp

@@ -792,8 +792,11 @@ bool DownloadUtxoSnapshot(const std::string& host,
 
     printf("Bootstrap: UTXO snapshot downloaded, loading into database...\n");
 
-    // Load the snapshot into a fresh active chain DB
-    if (!UtxoSnapshot::LoadSnapshot(tmpPath, dataDir, strError)) {
+    // Load the snapshot into a fresh active chain DB. P2P-delivered
+    // snapshots keep the checkpoint gate on (requireCheckpoint=true) —
+    // the manifest height+hash already passed IsKnownCheckpoint above,
+    // and we re-check here as defense in depth.
+    if (!UtxoSnapshot::LoadSnapshot(tmpPath, dataDir, strError, /*requireCheckpoint=*/true)) {
         fs::remove(tmpPath);
         return false;
     }

src/init.cpp

@@ -1025,8 +1025,13 @@ bool AppInit2()
             printf("Found utxo-snapshot.bin — loading UTXO snapshot...\n");
             uiInterface.InitMessage(_("Loading UTXO snapshot..."));
 
+            // Local file load: skip the checkpoint gate. The operator has
+            // filesystem access, so the trust model is already equivalent
+            // to direct chain state modification — a malicious local file
+            // is no worse than a malicious chain DB. P2P-delivered
+            // snapshots (SnapshotNet) keep the checkpoint gate on.
             std::string strError;
-            if (UtxoSnapshot::LoadSnapshot(snapshotFile, dataPath, strError)) {
+            if (UtxoSnapshot::LoadSnapshot(snapshotFile, dataPath, strError, /*requireCheckpoint=*/false)) {
                 printf("UTXO snapshot loaded successfully.\n");
             } else {
                 printf("UTXO snapshot load failed: %s\n", strError.c_str());

src/utxosnapshot.cpp

@@ -214,11 +214,20 @@ static bool SnapAddressFromScript(const CScript& script, int& nType, uint160& ha
 
 // ---------------------------------------------------------------------------
 // LoadSnapshot - load a UTXO snapshot into a fresh LevelDB
+//
+// `requireCheckpoint` controls whether the snapshot's tip block must be a
+// known checkpoint. This gate exists to prevent malicious P2P peers from
+// tricking the daemon into accepting a fake UTXO set at an arbitrary
+// height on an alternate chain. Local file loads (operator already has
+// filesystem access, so the trust model is the same as editing the chain
+// state directly) skip the gate via requireCheckpoint=false. P2P-delivered
+// snapshots (SnapshotNet) keep the gate on.
 // ---------------------------------------------------------------------------
 
 bool LoadSnapshot(const fs::path& snapshotPath,
                   const fs::path& /*dataDir — unused; resolved per-backend via GetChainDataDir()*/,
-                  std::string& strError)
+                  std::string& strError,
+                  bool requireCheckpoint)
 {
     FILE* file = fopen(snapshotPath.string().c_str(), "rb");
     if (!file) {
@@ -274,8 +283,9 @@ bool LoadSnapshot(const fs::path& snapshotPath,
         return false;
     }
 
-    // Verify snapshot block is a known checkpoint
-    if (!Checkpoints::IsKnownCheckpoint(height, blockHash)) {
+    // Verify snapshot block is a known checkpoint (only for P2P-delivered
+    // snapshots — local files are operator-trusted and can be at any height)
+    if (requireCheckpoint && !Checkpoints::IsKnownCheckpoint(height, blockHash)) {
         fclose(file);
         strError = "Snapshot block " + blockHash.ToString() + " at height "
                  + std::to_string(height) + " is not a known checkpoint";

src/utxosnapshot.h

@@ -29,10 +29,14 @@ namespace UtxoSnapshot {
     // Load a UTXO snapshot from a file into a fresh LevelDB.
     // Writes block index entries, UTXOs, hashBestChain, and dbformat.
     // The LevelDB must NOT be open yet (call before LoadBlockIndex).
+    // `requireCheckpoint` enforces that the snapshot tip is a known
+    // checkpoint (for P2P-delivered snapshots). Local loads from a
+    // trusted operator pass false.
     // Returns true on success, sets strError on failure.
     bool LoadSnapshot(const std::filesystem::path& snapshotPath,
                       const std::filesystem::path& dataDir,
-                      std::string& strError);
+                      std::string& strError,
+                      bool requireCheckpoint);
 
 } // namespace UtxoSnapshot