Add mutual exclusivity and k range validation

- Enforce exactly one of k, max_distance, or min_score
- Validate k is in [1, 10000] range
- Add 6 tests: mutual exclusivity (3 combos), k too small, k too
  large, k boundary values (1 and 10000)

Signed-off-by: Eric Wei <mengwei.eric@gmail.com>

Author: mengweieric

opensearch/src/main/java/org/opensearch/sql/opensearch/storage/VectorSearchTableFunctionImplementation.java

@@ -197,9 +197,20 @@ private void validateOptions(Map<String, String> options) {
       throw new ExpressionEvaluationException(
           "Missing required option: one of k, max_distance, or min_score");
     }
+    // Mutual exclusivity: exactly one search mode allowed
+    int modeCount = (hasK ? 1 : 0) + (hasMaxDistance ? 1 : 0) + (hasMinScore ? 1 : 0);
+    if (modeCount > 1) {
+      throw new ExpressionEvaluationException(
+          "Only one of k, max_distance, or min_score may be specified");
+    }
     // Parse and canonicalize numeric values — closes JSON injection via option values
     if (hasK) {
       parseIntOption(options, "k");
+      int k = Integer.parseInt(options.get("k"));
+      if (k < 1 || k > 10000) {
+        throw new ExpressionEvaluationException(
+            String.format("k must be between 1 and 10000, got %d", k));
+      }
     }
     if (hasMaxDistance) {
       parseDoubleOption(options, "max_distance");

opensearch/src/test/java/org/opensearch/sql/opensearch/storage/VectorSearchTableFunctionImplementationTest.java

@@ -233,6 +233,65 @@ void testInfiniteMinScoreThrows() {
     assertTrue(ex.getMessage().contains("must be a finite number"));
   }
 
+  @Test
+  void testMutualExclusivityKAndMaxDistanceThrows() {
+    VectorSearchTableFunctionImplementation impl =
+        createImplWithArgs("my-index", "embedding", "[1.0, 2.0]", "k=5,max_distance=10.0");
+    ExpressionEvaluationException ex =
+        assertThrows(ExpressionEvaluationException.class, () -> impl.applyArguments());
+    assertTrue(ex.getMessage().contains("Only one of"));
+  }
+
+  @Test
+  void testMutualExclusivityKAndMinScoreThrows() {
+    VectorSearchTableFunctionImplementation impl =
+        createImplWithArgs("my-index", "embedding", "[1.0, 2.0]", "k=5,min_score=0.5");
+    ExpressionEvaluationException ex =
+        assertThrows(ExpressionEvaluationException.class, () -> impl.applyArguments());
+    assertTrue(ex.getMessage().contains("Only one of"));
+  }
+
+  @Test
+  void testMutualExclusivityAllThreeThrows() {
+    VectorSearchTableFunctionImplementation impl =
+        createImplWithArgs(
+            "my-index", "embedding", "[1.0, 2.0]", "k=5,max_distance=10.0,min_score=0.5");
+    ExpressionEvaluationException ex =
+        assertThrows(ExpressionEvaluationException.class, () -> impl.applyArguments());
+    assertTrue(ex.getMessage().contains("Only one of"));
+  }
+
+  @Test
+  void testKTooSmallThrows() {
+    VectorSearchTableFunctionImplementation impl =
+        createImplWithArgs("my-index", "embedding", "[1.0, 2.0]", "k=0");
+    ExpressionEvaluationException ex =
+        assertThrows(ExpressionEvaluationException.class, () -> impl.applyArguments());
+    assertTrue(ex.getMessage().contains("k must be between 1 and 10000"));
+  }
+
+  @Test
+  void testKTooLargeThrows() {
+    VectorSearchTableFunctionImplementation impl =
+        createImplWithArgs("my-index", "embedding", "[1.0, 2.0]", "k=10001");
+    ExpressionEvaluationException ex =
+        assertThrows(ExpressionEvaluationException.class, () -> impl.applyArguments());
+    assertTrue(ex.getMessage().contains("k must be between 1 and 10000"));
+  }
+
+  @Test
+  void testKBoundaryValuesAllowed() {
+    // k=1 should work
+    VectorSearchTableFunctionImplementation impl1 =
+        createImplWithArgs("my-index", "embedding", "[1.0, 2.0]", "k=1");
+    assertTrue(impl1.applyArguments() instanceof VectorSearchIndex);
+
+    // k=10000 should work
+    VectorSearchTableFunctionImplementation impl2 =
+        createImplWithArgs("my-index", "embedding", "[1.0, 2.0]", "k=10000");
+    assertTrue(impl2.applyArguments() instanceof VectorSearchIndex);
+  }
+
   @Test
   void testNonNamedArgThrows() {
     FunctionName functionName = FunctionName.of("vectorsearch");