perf: run the contiguous UPDATE/DELETE fast paths on plaintext default-config tables

The bulk fast paths previously required DatabaseConfig.NoEncryptMode, although per-record encryption is opt-in (EnableAtRestRecordEncryption): default-config databases already store plaintext records. Gate on the storage layer's runtime AreRecordsEncrypted (UseRecordEncryption && file carries the encrypted magic header) instead of the config flag, so default-config users get the single-pass UPDATE/DELETE path too; genuinely encrypted tables still fall back to the generic loop.

Author: MPCoreDeveloper

src/SharpCoreDB/DataStructures/Table.CRUD.cs

@@ -2356,15 +2356,16 @@ private bool TryBulkUpdateContiguousFixedWidth(
         }
 
         // Narrow, conservative gate: fixed-width columnar table with an explicit PK, plaintext
-        // records only (a raw contiguous read must equal the logical record bytes), no buffered
-        // overwrites for this file, and no CHECK constraints (mirrors the generic fastPatch gate).
+        // records only (no per-record encryption magic — a raw contiguous read must equal the
+        // logical record bytes), no buffered overwrites for this file, and no CHECK constraints
+        // (mirrors the generic fastPatch gate).
         if (!_fixedWidthRecords ||
             StorageMode != StorageMode.Columnar ||
             this.PrimaryKeyIndex < 0 ||
             this.TableCheckConstraints.Count > 0 ||
             HasColumnCheckConstraints() ||
             this.storage is null ||
-            this._config is not { NoEncryptMode: true } ||
+            this.storage.AreRecordsEncrypted(DataFile) ||
             this.storage.HasBufferedOverwrite(DataFile))
         {
             return false;
@@ -3047,13 +3048,14 @@ private bool TryBulkDeleteContiguousFixedWidth(List<string> whereConditions)
         }
 
         // Identical safety gate to the UPDATE fast path: fixed-width columnar table with an explicit
-        // PK, plaintext records only, and no buffered overwrites (a raw range read must equal the
-        // logical record bytes). DeleteMultiple loads every registered hash index before calling this.
+        // PK, plaintext records only (no per-record encryption magic — a raw range read must equal
+        // the logical record bytes), and no buffered overwrites. DeleteMultiple loads every
+        // registered hash index before calling this.
         if (!_fixedWidthRecords ||
             StorageMode != StorageMode.Columnar ||
             this.PrimaryKeyIndex < 0 ||
             this.storage is null ||
-            this._config is not { NoEncryptMode: true } ||
+            this.storage.AreRecordsEncrypted(DataFile) ||
             this.storage.HasBufferedOverwrite(DataFile))
         {
             return false;

src/SharpCoreDB/Interfaces/IStorage.cs

@@ -163,6 +163,13 @@ bool OverwriteRecordAtSameLength(string path, long offset, byte[] data) =>
     /// </summary>
     byte[]? ReadBytesRange(string path, long offset, int length) => null;
 
+    /// <summary>
+    /// True when the file at <paramref name="path"/> stores per-record encrypted (ciphertext)
+    /// payloads (it carries the encrypted-table magic header). Raw range reads must never be used on
+    /// such files; the default returns false (plaintext / legacy layouts).
+    /// </summary>
+    bool AreRecordsEncrypted(string path) => false;
+
     /// <summary>
     /// Enumerates every record in a table data file, yielding the literal file offset of the
     /// 4-byte length prefix (the offset returned by <see cref="AppendBytes"/>) together with the

src/SharpCoreDB/Services/Storage.Append.cs

@@ -560,6 +560,9 @@ public bool OverwriteRecordAtSameLength(string path, long offset, byte[] data)
     public bool HasBufferedOverwrite(string path) =>
         !bufferedOverwrites.IsEmpty && bufferedOverwrites.ContainsKey(path);
 
+    /// <inheritdoc />
+    public bool AreRecordsEncrypted(string path) => UseRecordEncryption && FileHasEncryptedHeader(path);
+
     /// <inheritdoc />
     [MethodImpl(MethodImplOptions.AggressiveOptimization)]
     public long[] AppendBytesMultiple(string path, List<byte[]> dataBlocks)

tests/SharpCoreDB.Tests/FixedWidthBulkUpdateTests.cs

@@ -42,6 +42,9 @@ public void Dispose()
     private IDatabase CreateDb(bool noEncrypt = true) => _factory.Create(_dirPath, "pw", isReadOnly: false,
         config: new DatabaseConfig { NoEncryptMode = noEncrypt });
 
+    private IDatabase CreateEncryptedDb() => _factory.Create(_dirPath, "pw", isReadOnly: false,
+        config: new DatabaseConfig { NoEncryptMode = false, EnableAtRestRecordEncryption = true });
+
     private static Table TableOf(IDatabase db, string tableName)
     {
         Assert.True(db.TryGetTable(tableName, out var t));
@@ -209,9 +212,11 @@ public void IndexedColumnUpdate_FallsBack_AndRepointsIndex()
     }
 
     [Fact]
-    public void EncryptedOrDefaultConfig_FallsBack_AndStaysCorrect()
+    public void DefaultPlaintextConfig_EngagesBulkPath_AndStaysCorrect()
     {
-        var db = CreateDb(noEncrypt: false); // default config: the gate requires NoEncryptMode
+        // Default config (no NoEncryptMode) stores plaintext records unless per-record encryption
+        // is opted in, so the runtime magic-header gate now admits the fast path here too.
+        var db = CreateDb(noEncrypt: false);
         try
         {
             db.ExecuteSQL("CREATE TABLE docs (id INTEGER PRIMARY KEY, name TEXT, score REAL)");
@@ -221,7 +226,29 @@ public void EncryptedOrDefaultConfig_FallsBack_AndStaysCorrect()
             var table = TableOf(db, "docs");
             db.ExecuteBatchSQL(BuildUpdates(1, 300, "score = 4.25"));
             db.Flush();
-            Assert.Equal(0, table.BulkContiguousUpdateBatches);
+            Assert.Equal(1, table.BulkContiguousUpdateBatches);
+
+            var rows = db.ExecuteQuery("SELECT score FROM docs WHERE id = 300");
+            Assert.Single(rows);
+            Assert.Equal(4.25, Convert.ToDouble(rows[0]["score"]));
+        }
+        finally { (db as IDisposable)?.Dispose(); }
+    }
+
+    [Fact]
+    public void PerRecordEncryption_FallsBackToGenericLoop_AndStaysCorrect()
+    {
+        var db = CreateEncryptedDb();
+        try
+        {
+            db.ExecuteSQL("CREATE TABLE docs (id INTEGER PRIMARY KEY, name TEXT, score REAL)");
+            InsertDocs(db, 1, 300);
+            db.Flush();
+
+            var table = TableOf(db, "docs");
+            db.ExecuteBatchSQL(BuildUpdates(1, 300, "score = 4.25"));
+            db.Flush();
+            Assert.Equal(0, table.BulkContiguousUpdateBatches); // ciphertext records → generic loop
 
             var rows = db.ExecuteQuery("SELECT score FROM docs WHERE id = 300");
             Assert.Single(rows);