fix: keep node file content byte-faithful in node_file_get

Splitting the file with keepends=False and rejoining with newlines
dropped the trailing newline of the last line (and every \r of CRLF
files), so returned content was shorter than the file on disk and did
not round-trip. Split with keepends=True and join the selected lines
verbatim; pagination semantics are unchanged.

tests/agent/mcp/test_handlers.py

@@ -242,6 +242,49 @@ class TestNode:
             result = get_node_console_info_handler({"project_id": "p1", "node_id": "n1"}, ctx)
             assert "command" in result
 
+    @staticmethod
+    def _file_conn(text):
+        conn = _mock_conn()
+        conn.http_call.return_value.text = text
+        return conn
+
+    def test_file_get_keeps_trailing_newline(self, ctx):
+        from gns3server.agent.gns3_copilot.gns3_client.api_handlers import get_node_file_handler
+        with patch(f"{AH}._get_connector") as m:
+            m.return_value = self._file_conn("line1\nline2\n")
+            result = get_node_file_handler({"project_id": "p1", "node_id": "n1", "file_path": "startup.cfg"}, ctx)
+            assert result["content"] == "line1\nline2\n"
+            assert result["metadata"]["total_bytes"] == 12
+            assert result["metadata"]["returned_bytes"] == 12
+            assert result["metadata"]["has_more"] is False
+
+    def test_file_get_keeps_crlf_endings(self, ctx):
+        from gns3server.agent.gns3_copilot.gns3_client.api_handlers import get_node_file_handler
+        with patch(f"{AH}._get_connector") as m:
+            m.return_value = self._file_conn("line1\r\nline2\r\n")
+            result = get_node_file_handler({"project_id": "p1", "node_id": "n1", "file_path": "startup.cfg"}, ctx)
+            assert result["content"] == "line1\r\nline2\r\n"
+            assert result["metadata"]["returned_bytes"] == 14
+
+    def test_file_get_without_trailing_newline(self, ctx):
+        from gns3server.agent.gns3_copilot.gns3_client.api_handlers import get_node_file_handler
+        with patch(f"{AH}._get_connector") as m:
+            m.return_value = self._file_conn("line1\nline2")
+            result = get_node_file_handler({"project_id": "p1", "node_id": "n1", "file_path": "startup.cfg"}, ctx)
+            assert result["content"] == "line1\nline2"
+
+    def test_file_get_pagination(self, ctx):
+        from gns3server.agent.gns3_copilot.gns3_client.api_handlers import get_node_file_handler
+        with patch(f"{AH}._get_connector") as m:
+            m.return_value = self._file_conn("line1\nline2\nline3\n")
+            result = get_node_file_handler(
+                {"project_id": "p1", "node_id": "n1", "file_path": "startup.cfg", "offset": 1, "limit": 1}, ctx
+            )
+            assert result["content"] == "line2\n"
+            assert result["metadata"]["total_lines"] == 3
+            assert result["metadata"]["returned_lines"] == 1
+            assert result["metadata"]["has_more"] is True
+
 
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