Update error messages for the AI agent

Author: sualeh

schemacrawler-ai-mcpserver/src/main/java/schemacrawler/tools/ai/mcpserver/EmptyCatalog.java

@@ -32,6 +32,25 @@ public class EmptyCatalog implements Catalog {
 
   private static final long serialVersionUID = -8018517276190501450L;
 
+  private final String errorMessage;
+
+  public EmptyCatalog(final Exception e) {
+    final String baseErrorMessage =
+        """
+        The MCP server is in an error state, since it could not
+        make a connection to the database. Database schema metadata
+        is not available.
+        """
+                .strip()
+                .trim()
+            + "\n";
+    if (e != null) {
+      errorMessage = baseErrorMessage + e.getMessage();
+    } else {
+      errorMessage = baseErrorMessage;
+    }
+  }
+
   @Override
   public int compareTo(final NamedObject o) {
     return -1;
@@ -64,12 +83,12 @@ public Collection<ColumnDataType> getColumnDataTypes(final Schema schema) {
 
   @Override
   public CrawlInfo getCrawlInfo() {
-    throw new UnsupportedOperationException("No supported in an empty catalog");
+    throw new UnsupportedOperationException(errorMessage);
   }
 
   @Override
   public DatabaseInfo getDatabaseInfo() {
-    throw new UnsupportedOperationException("No supported in an empty catalog");
+    throw new UnsupportedOperationException(errorMessage);
   }
 
   @Override
@@ -84,7 +103,7 @@ public String getFullName() {
 
   @Override
   public JdbcDriverInfo getJdbcDriverInfo() {
-    throw new UnsupportedOperationException("No supported in an empty catalog");
+    throw new UnsupportedOperationException(errorMessage);
   }
 
   @Override

schemacrawler-ai-mcpserver/src/main/java/schemacrawler/tools/ai/mcpserver/McpServerMain.java

@@ -57,7 +57,7 @@ private static Catalog getCatalog(final McpServerContext context) {
       if (!ConnectionService.isInstantiated()) {
         ConnectionService.instantiate(new EmptyDatabaseConnectionSource());
       }
-      return new EmptyCatalog();
+      return new EmptyCatalog(e);
     }
   }
 }