From 1b603eaded20ff8f742e14bb8f29b792d504503e Mon Sep 17 00:00:00 2001
From: mikemikimike <13286568797@163.com>
Date: Fri, 28 Aug 2026 14:32:18 +0800
Subject: [PATCH] fix: preserve shell environment over dotenv files

---
 aider/main.py            | 24 +++++++++++++++---------
 tests/basic/test_main.py | 13 +++++++++++++
 2 files changed, 28 insertions(+), 9 deletions(-)

diff --git a/aider/main.py b/aider/main.py
index afb3f836624..bebf1e76fc1 100644
--- a/aider/main.py
+++ b/aider/main.py
@@ -374,16 +374,22 @@ def load_dotenv_files(git_root, dotenv_fname, encoding="utf-8"):
         # Remove duplicates if it somehow got included by generate_search_path_list
         dotenv_files = list(dict.fromkeys(dotenv_files))
 
+    existing_env = os.environ.copy()
     loaded = []
-    for fname in dotenv_files:
-        try:
-            if Path(fname).exists():
-                load_dotenv(fname, override=True, encoding=encoding)
-                loaded.append(fname)
-        except OSError as e:
-            print(f"OSError loading {fname}: {e}")
-        except Exception as e:
-            print(f"Error loading {fname}: {e}")
+    try:
+        for fname in dotenv_files:
+            try:
+                if Path(fname).exists():
+                    load_dotenv(fname, override=True, encoding=encoding)
+                    loaded.append(fname)
+            except OSError as e:
+                print(f"OSError loading {fname}: {e}")
+            except Exception as e:
+                print(f"Error loading {fname}: {e}")
+    finally:
+        # Keep values explicitly provided by the user ahead of dotenv files.
+        for key, value in existing_env.items():
+            os.environ[key] = value
     return loaded
 
 
diff --git a/tests/basic/test_main.py b/tests/basic/test_main.py
index c8966a53671..f45c47aa4a5 100644
--- a/tests/basic/test_main.py
+++ b/tests/basic/test_main.py
@@ -1470,6 +1470,19 @@ def test_load_dotenv_files_override(self):
             # Restore CWD
             os.chdir(original_cwd)
 
+    def test_load_dotenv_files_does_not_override_existing_env(self):
+        with GitTemporaryDirectory() as git_dir:
+            git_dir = Path(git_dir)
+            env_file = git_dir / ".env"
+            env_file.write_text("EXISTING_VAR=file_value\nFILE_ONLY_VAR=file_value\n")
+
+            with patch.dict(os.environ, {"EXISTING_VAR": "shell_value"}, clear=False):
+                with patch("pathlib.Path.home", return_value=git_dir / "fake_home"):
+                    load_dotenv_files(str(git_dir), None)
+
+                self.assertEqual(os.environ.get("EXISTING_VAR"), "shell_value")
+                self.assertEqual(os.environ.get("FILE_ONLY_VAR"), "file_value")
+
     @patch("aider.main.InputOutput")
     def test_cache_without_stream_no_warning(self, MockInputOutput):
         mock_io_instance = MockInputOutput.return_value