Fix debugger messages from successive steps running together on one line. #8664 (#10544)

Each poll of the debugger returns its own batch of notices without a
trailing newline, so appending them directly ran messages from separate
steps together. Start each appended batch on a new line.
- Clarify that debugger message batches only usually lack a trailing newline.

Author: dpage

web/pgadmin/tools/debugger/static/js/components/DebuggerMessages.jsx

@@ -25,7 +25,12 @@ export default function DebuggerMessages() {
     eventBus.registerListener(DEBUGGER_EVENTS.SET_MESSAGES, (text, append=false)=>{
       setMessageText((prev)=>{
         if(append) {
-          return prev+text;
+          // Each poll returns its own batch of messages, usually without a
+          // trailing newline, so start every appended batch on a new line.
+          if(prev && !prev.endsWith('\n')) {
+            return prev + '\n' + text;
+          }
+          return prev + text;
         }
         return text;
       });

web/regression/javascript/debugger/debugger_messages_spec.js

@@ -0,0 +1,52 @@
+/////////////////////////////////////////////////////////////
+//
+// pgAdmin 4 - PostgreSQL Tools
+//
+// Copyright (C) 2013 - 2026, The pgAdmin Development Team
+// This software is released under the PostgreSQL Licence
+//
+//////////////////////////////////////////////////////////////
+
+import { render, act } from '@testing-library/react';
+
+import EventBus from '../../../pgadmin/static/js/helpers/EventBus';
+import { DebuggerEventsContext } from '../../../pgadmin/tools/debugger/static/js/components/DebuggerComponent';
+import DebuggerMessages from '../../../pgadmin/tools/debugger/static/js/components/DebuggerMessages';
+import { DEBUGGER_EVENTS } from '../../../pgadmin/tools/debugger/static/js/DebuggerConstants';
+
+
+describe('Debugger Messages', () => {
+  let eventBus;
+
+  const renderMessages = () => {
+    eventBus = new EventBus();
+    const ctrl = render(
+      <DebuggerEventsContext.Provider value={eventBus}>
+        <DebuggerMessages />
+      </DebuggerEventsContext.Provider>
+    );
+    return ctrl.container.querySelector('#debugger-msg');
+  };
+
+  it('puts each appended batch of messages on a new line', async () => {
+    const msgDiv = renderMessages();
+    await act(async () => {
+      eventBus.fireEvent(DEBUGGER_EVENTS.SET_MESSAGES, 'NOTICE:  first', true);
+      eventBus.fireEvent(DEBUGGER_EVENTS.SET_MESSAGES, 'NOTICE:  second', true);
+      eventBus.fireEvent(DEBUGGER_EVENTS.SET_MESSAGES, 'NOTICE:  third\n', true);
+      eventBus.fireEvent(DEBUGGER_EVENTS.SET_MESSAGES, 'NOTICE:  fourth', true);
+    });
+    expect(msgDiv.textContent).toBe(
+      'NOTICE:  first\nNOTICE:  second\nNOTICE:  third\nNOTICE:  fourth'
+    );
+  });
+
+  it('replaces the messages when not appending', async () => {
+    const msgDiv = renderMessages();
+    await act(async () => {
+      eventBus.fireEvent(DEBUGGER_EVENTS.SET_MESSAGES, 'NOTICE:  old', true);
+      eventBus.fireEvent(DEBUGGER_EVENTS.SET_MESSAGES, 'NOTICE:  new');
+    });
+    expect(msgDiv.textContent).toBe('NOTICE:  new');
+  });
+});