fix: exclude pg_stat_statements functions from Brain schema introspection

- Added EXCLUDED_EXTENSION_FUNCTIONS_SQL constant to filter out pg_stat_statements,
  pg_stat_statements_info, pg_stat_statements_reset, and pg_buffercache functions
- Applied excludeExtensionFunctionsPredicate to getFunctions() query
- Extended tests to verify function exclusion works correctly

The view exclusion was already working but the extension also creates functions
that appeared in Brain. This adds the missing function filter.

Co-authored-by: Venkat SF <venkatesh.sakamuri@stayflexi.com>

Author: cursoragent

backend/src/main/java/com/dbaagent/provider/postgres/PostgresIntrospectionProvider.java

@@ -37,6 +37,13 @@ public class PostgresIntrospectionProvider implements IntrospectionProvider {
     static final String EXCLUDED_EXTENSION_VIEWS_SQL =
         "NOT IN ('pg_stat_statements', 'pg_stat_statements_info', 'pg_buffercache')";
 
+    /**
+     * Extension-created functions that should be excluded from Brain. These are
+     * internal extension functions not useful for application queries.
+     */
+    static final String EXCLUDED_EXTENSION_FUNCTIONS_SQL =
+        "NOT IN ('pg_stat_statements', 'pg_stat_statements_info', 'pg_stat_statements_reset', 'pg_buffercache_pages', 'pg_buffercache_summary')";
+
     static String nonSystemSchemaPredicate(String column) {
         return column + " " + String.format(NON_SYSTEM_SCHEMA_SQL, column);
     }
@@ -45,6 +52,10 @@ static String excludeExtensionViewsPredicate(String column) {
         return column + " " + EXCLUDED_EXTENSION_VIEWS_SQL;
     }
 
+    static String excludeExtensionFunctionsPredicate(String column) {
+        return column + " " + EXCLUDED_EXTENSION_FUNCTIONS_SQL;
+    }
+
     /** Map / snapshot key that survives duplicate table names across schemas. */
     static String qualifiedTableKey(String schema, String table) {
         String s = (schema == null || schema.isBlank()) ? DEFAULT_SCHEMA : schema;
@@ -128,13 +139,15 @@ private List<DatabaseObject> getTablesAndViews(Connection connection) throws SQL
     private List<DatabaseObject> getFunctions(Connection connection) throws SQLException {
         List<DatabaseObject> objects = new ArrayList<>();
 
+        String schemaPred = nonSystemSchemaPredicate("n.nspname");
+        String extFuncPred = excludeExtensionFunctionsPredicate("p.proname");
         String query = """
             SELECT n.nspname as schema_name, p.proname as name, pg_get_functiondef(p.oid) as definition
             FROM pg_proc p
             JOIN pg_namespace n ON p.pronamespace = n.oid
-            WHERE %s AND p.prokind = 'f'
+            WHERE %s AND %s AND p.prokind = 'f'
             ORDER BY n.nspname, p.proname
-            """.formatted(nonSystemSchemaPredicate("n.nspname"));
+            """.formatted(schemaPred, extFuncPred);
 
         try (Statement stmt = connection.createStatement();
              ResultSet rs = stmt.executeQuery(query)) {

backend/src/test/java/com/dbaagent/provider/postgres/PostgresIntrospectionProviderTest.java

@@ -412,4 +412,30 @@ void extensionViewExclusion_isExactMatch() {
         assertTrue(predicate.startsWith("NOT IN"),
             "Predicate should use NOT IN for exact matching");
     }
+
+    @Test
+    void excludeExtensionFunctionsPredicate_excludesPgStatStatementsFunctions() {
+        String predicate = PostgresIntrospectionProvider.excludeExtensionFunctionsPredicate("p.proname");
+        
+        assertTrue(predicate.contains("pg_stat_statements"),
+            "Exclusion predicate should mention pg_stat_statements");
+        assertTrue(predicate.contains("pg_stat_statements_info"),
+            "Exclusion predicate should mention pg_stat_statements_info");
+        assertTrue(predicate.contains("pg_stat_statements_reset"),
+            "Exclusion predicate should mention pg_stat_statements_reset");
+        assertTrue(predicate.contains("NOT IN"),
+            "Exclusion predicate should use NOT IN clause");
+    }
+
+    @Test
+    void extensionFunctionExclusion_isExactMatch() {
+        String predicate = PostgresIntrospectionProvider.EXCLUDED_EXTENSION_FUNCTIONS_SQL;
+        
+        assertTrue(predicate.contains("'pg_stat_statements'"),
+            "Predicate should exclude exactly 'pg_stat_statements'");
+        assertTrue(predicate.contains("'pg_stat_statements_reset'"),
+            "Predicate should exclude exactly 'pg_stat_statements_reset'");
+        assertTrue(predicate.startsWith("NOT IN"),
+            "Predicate should use NOT IN for exact matching");
+    }
 }