fix(dameng): use ALTER TABLE constraints for unique indexes

agents/common/src/main/java/com/dbx/agent/IndexInfo.java

@@ -18,6 +18,12 @@ public final class IndexInfo {
     // doesn't track this (provenance unknown for that dialect/path). Mirrors
     // crate::types::IndexInfo::key_is_expression on the Rust side (#6312 review).
     private List<Boolean> key_is_expression;
+    // True when this index is the object behind a table constraint (PRIMARY KEY / UNIQUE)
+    // instead of a standalone index. Dameng lists both kinds in ALL_INDEXES but only accepts
+    // index-level DDL for standalone ones, so the SQL builder needs to tell them apart
+    // (#7959). Mirrors crate::types::IndexInfo::constraint_backed on the Rust side; false
+    // when the introspection source doesn't report it.
+    private boolean constraint_backed;
 
     public IndexInfo() {
         this("", Collections.emptyList(), false, false);
@@ -98,6 +104,10 @@ public final class IndexInfo {
         return key_is_expression;
     }
 
+    public boolean getConstraint_backed() {
+        return constraint_backed;
+    }
+
     public void setName(String name) {
         this.name = name;
     }
@@ -134,6 +144,10 @@ public final class IndexInfo {
         this.key_is_expression = key_is_expression;
     }
 
+    public void setConstraint_backed(boolean constraint_backed) {
+        this.constraint_backed = constraint_backed;
+    }
+
     @Override
     public boolean equals(Object other) {
         if (this == other) return true;
@@ -141,6 +155,7 @@ public final class IndexInfo {
         IndexInfo that = (IndexInfo) other;
         return is_unique == that.is_unique
             && is_primary == that.is_primary
+            && constraint_backed == that.constraint_backed
             && Objects.equals(name, that.name)
             && Objects.equals(columns, that.columns)
             && Objects.equals(filter, that.filter)
@@ -153,7 +168,16 @@ public final class IndexInfo {
     @Override
     public int hashCode() {
         return Objects.hash(
-            name, columns, is_unique, is_primary, filter, index_type, included_columns, comment, key_is_expression
+            name,
+            columns,
+            is_unique,
+            is_primary,
+            filter,
+            index_type,
+            included_columns,
+            comment,
+            key_is_expression,
+            constraint_backed
         );
     }
 
@@ -168,6 +192,7 @@ public final class IndexInfo {
             + ", included_columns=" + included_columns
             + ", comment=" + comment
             + ", key_is_expression=" + key_is_expression
+            + ", constraint_backed=" + constraint_backed
             + ")";
     }
 }