fix: auto-download UTXO snapshot when chain DB missing (3 root causes)

Three bugs prevented the wallet from automatically downloading the UTXO
snapshot when starting with stale blk0001.dat but no chain database:

1. NeedsBootstrap() only checked for blk0001.dat existence, not the chain
   DB. If blk0001.dat was present (leftover from old version) but
   txleveldb/chainstate was missing, it reported "no bootstrap needed"
   and the snapshot download never triggered.

   Fix: check for txleveldb/ or blocks/chainstate/ instead.

2. Bootstrap HTTP download was skipped when snapshotMode was true (the
   default). The code deferred to P2P snapshot fetch (Step 11.6), but
   that runs AFTER Step 7 which errored out on the FastImport gate.

   Fix: always attempt HTTP bootstrap when NeedsBootstrap is true,
   regardless of snapshotMode. The UTXO snapshot HTTP download IS the
   fast path — no reason to defer to P2P when HTTP is available.

3. FastImport gate (Step 7) was a hard InitError that killed the daemon
   before it ever reached the snapshot fetch path. blk0001.dat present
   + no chain index + FastImport disabled = immediate crash.

   Fix: instead of erroring, remove the stale blk0001.dat and continue.
   The daemon syncs from the snapshot that was already loaded in Step 6b,
   or from P2P if that somehow failed.

src/bootstrap.cpp

@@ -50,7 +50,14 @@ namespace Bootstrap {
 
 bool NeedsBootstrap(const fs::path& dataDir)
 {
-    return !fs::exists(dataDir / "blk0001.dat");
+    // Need bootstrap if there's no chain database (the UTXO set / block index).
+    // blk0001.dat alone is NOT sufficient — it's raw block data that requires
+    // FastImport to build an index, and FastImport is disabled by default.
+    // Check for both LevelDB (txleveldb/) and RocksDB (chainstate/) backends.
+    bool hasChainDb = fs::exists(dataDir / "txleveldb")
+                   || fs::exists(dataDir / "blocks" / "chainstate")
+                   || fs::exists(dataDir / "chainstate");
+    return !hasChainDb;
 }
 
 // Direct TCP connection bypassing Tor SOCKS proxy.

src/init.cpp

@@ -1030,14 +1030,11 @@ bool AppInit2()
         fs::path dataPath = GetDataDir();
         bool needsBootstrap = Bootstrap::NeedsBootstrap(dataPath);
 
-        if (needsBootstrap && !noBootstrap && !snapshotMode) {
-            printf("Bootstrap: no blockchain data found — downloading automatically.\n");
+        if (needsBootstrap && !noBootstrap) {
+            printf("Bootstrap: no blockchain data found — downloading UTXO snapshot automatically.\n");
             printf("Bootstrap: (use -nobootstrap to skip)\n");
-            uiInterface.InitMessage(_("Downloading blockchain data..."));
+            uiInterface.InitMessage(_("Downloading UTXO snapshot..."));
             wantsBootstrap = true;
-        } else if (needsBootstrap && snapshotMode && !wantsBootstrap) {
-            printf("Bootstrap: no blockchain data found — will fetch UTXO snapshot via P2P after network start.\n");
-            printf("Bootstrap: (use -bootstrap for legacy clearnet HTTP bootstrap, or -snapshot=0 to disable P2P fetcher)\n");
         }
 
     if (wantsBootstrap)
@@ -1229,20 +1226,20 @@ bool AppInit2()
     {
         if (!GetBoolArg("-allowfastimport", false))
         {
-            return InitError(_(
-                "Block index empty and blk0001.dat is present, but FastImport is disabled "
-                "(default). The snapshot path is the only supported sync start.\n\n"
-                "To recover:\n"
-                "  1. Place a signed utxo-snapshot.bin in the data directory and restart, OR\n"
-                "  2. Delete blk0001.dat (the snapshot path will sync from network), OR\n"
-                "  3. Pass -allowfastimport=1 to permit FastImport (operator opt-in only)."));
+            printf("FastImport: blk0001.dat present but -allowfastimport not set — "
+                   "ignoring block file, will sync from network via UTXO snapshot.\n");
+            // Remove the stale blk0001.dat so it doesn't trigger again
+            std::filesystem::remove(GetDataDir() / "blk0001.dat");
         }
+        else
+        {
         printf("FastImport: WARNING -allowfastimport is set; rebuilding from local blk0001.dat.\n");
         uiInterface.InitMessage(_("Importing bootstrap blocks..."));
         printf("Block index empty but blk0001.dat exists - running fast import...\n");
         int64_t nFastImportStart = GetTimeMillis();
         FastImportBlockFile();
         StartupPerfLog("bootstrap_fast_import", GetTimeMillis() - nFastImportStart, strprintf("bestheight=%d", nBestHeight));
+        }
     }
 
     // as LoadBlockIndex can take several minutes, it's possible the user