diff --git a/CHANGELOG.md b/CHANGELOG.md
index 8378e53..4c824c5 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -5,6 +5,12 @@ All notable changes to this project will be documented in this file.
 The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.1.0/),
 and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.html).
 
+## [0.12.2] - 2026-03-31
+
+### Fixed
+
+- **config** — File I/O errors (missing or unreadable `.env`/JSON files) and JSON parse errors are now classified as `errors.Internal` instead of `errors.BadRequest`; error message updated from `"file not found"` to `"cannot open file"` to better reflect the server-side cause
+
 ## [0.12.1] - 2026-03-30
 
 ### Fixed
diff --git a/config/config_test.go b/config/config_test.go
index 0801099..ec8aa7d 100644
--- a/config/config_test.go
+++ b/config/config_test.go
@@ -323,8 +323,8 @@ func TestLoad_EnvFileMissing_Required(t *testing.T) {
 	if err == nil {
 		t.Fatal("expected error for missing required env file")
 	}
-	if !strings.Contains(err.Error(), "file not found") {
-		t.Errorf("error = %q, want it to contain 'file not found'", err.Error())
+	if !strings.Contains(err.Error(), "cannot open file") {
+		t.Errorf("error = %q, want it to contain 'cannot open file'", err.Error())
 	}
 }
 
diff --git a/config/env.go b/config/env.go
index 1e7279f..31a229a 100644
--- a/config/env.go
+++ b/config/env.go
@@ -18,7 +18,7 @@ func loadEnvFile(path string, required bool) (map[string]string, error) {
 		if os.IsNotExist(err) && !required {
 			return nil, nil
 		}
-		return nil, errors.BadRequest("config: file not found: " + path)
+		return nil, errors.Internal("config: cannot open file: " + path)
 	}
 	defer func() { _ = f.Close() }()
 
diff --git a/config/json.go b/config/json.go
index 46fd0c0..47cafeb 100644
--- a/config/json.go
+++ b/config/json.go
@@ -19,12 +19,12 @@ func loadJSONFile(path string, required bool) (map[string]string, error) {
 		if os.IsNotExist(err) && !required {
 			return nil, nil
 		}
-		return nil, errors.BadRequest("config: file not found: " + path)
+		return nil, errors.Internal("config: cannot open file: " + path)
 	}
 
 	var raw map[string]any
 	if err := json.Unmarshal(data, &raw); err != nil {
-		return nil, errors.BadRequest(fmt.Sprintf("config: invalid JSON in %s: %v", path, err))
+		return nil, errors.Internal(fmt.Sprintf("config: invalid JSON in %s: %v", path, err))
 	}
 
 	result := make(map[string]string)