Reject empty vector payloads in VADD and VSIM

Add a common values.IsEmpty check after all type-specific branches
in both VADD and VSIM to reject zero-dimension vector requests with
a clear error instead of passing them through to DiskANN. The FP32
alignment check remains in the FP32-specific branch.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Author: harsha-simhadri

libs/server/Resp/Vector/RespServerSessionVectors.cs

@@ -142,6 +142,11 @@ private bool NetworkVADD<TGarnetApi>(ref TGarnetApi storageApi)
                     values = asBytes;
                 }
 
+                if (values.IsEmpty)
+                {
+                    return AbortWithErrorMessage("ERR vector values must be non-empty");
+                }
+
                 if (curIx >= parseState.Count)
                 {
                     return AbortWithWrongNumberOfArguments("VADD");
@@ -587,6 +592,11 @@ private bool NetworkVSIM<TGarnetApi>(ref TGarnetApi storageApi)
                     }
                 }
 
+                if (!element.HasValue && values.IsEmpty)
+                {
+                    return AbortWithErrorMessage("ERR vector values must be non-empty");
+                }
+
                 bool? withScores = null;
                 bool? withAttributes = null;
                 int? count = null;

test/Garnet.test/RespVectorSetTests.cs

@@ -405,6 +405,14 @@ public void VADDErrors()
             var exc15 = ClassicAssert.Throws<RedisServerException>(() => db.Execute("VADD", [vectorSetKey, "FP32", blob, "bar"]));
             ClassicAssert.AreEqual("ERR invalid vector specification", exc15.Message);
 
+            // Empty vector payloads should be rejected for all binary types
+            var excEmptyFP32 = ClassicAssert.Throws<RedisServerException>(() => db.Execute("VADD", [vectorSetKey, "FP32", Array.Empty<byte>(), "bar"]));
+            ClassicAssert.AreEqual("ERR vector values must be non-empty", excEmptyFP32.Message);
+            var excEmptyXB8 = ClassicAssert.Throws<RedisServerException>(() => db.Execute("VADD", [vectorSetKey, "XB8", Array.Empty<byte>(), "bar"]));
+            ClassicAssert.AreEqual("ERR vector values must be non-empty", excEmptyXB8.Message);
+            var excEmptySB8 = ClassicAssert.Throws<RedisServerException>(() => db.Execute("VADD", [vectorSetKey, "SB8", Array.Empty<byte>(), "bar"]));
+            ClassicAssert.AreEqual("ERR vector values must be non-empty", excEmptySB8.Message);
+
             // Mismatch after creating a vector set
             _ = db.KeyDelete(vectorSetKey);