Fix newline handling when appending to .env

Taskfile.yaml

@@ -22,6 +22,11 @@ tasks:
       - cargo clippy --all-targets --all-features -- -D warnings
       - cargo test --all-features
 
+  lint:fix:
+    desc: "Auto-fix clippy lints where possible (same scope as `task test`)"
+    cmds:
+      - cargo clippy --fix --all-targets --all-features --allow-dirty --allow-staged
+
   build:
     desc: "Build debug binary for the host"
     silent: true

src/handlers/set_value.rs

@@ -34,10 +34,16 @@ pub fn set_value(options: &Options) {
         fs::write(&options.full_env_path, lines.join("\n")).expect("Failed to write .env file");
     } else {
         // Append new key to end of file
+        let existing = fs::read(&options.full_env_path).expect("Failed to read .env file");
+        let needs_leading_newline = !existing.is_empty() && existing.last() != Some(&b'\n');
+
         let mut file = fs::OpenOptions::new()
             .append(true)
             .open(&options.full_env_path)
             .expect("Failed to open .env file for appending");
+        if needs_leading_newline {
+            writeln!(file).expect("Failed to append to .env file");
+        }
         writeln!(file, "{}", new_line).expect("Failed to append to .env file");
     }
 }

tests/set_and_delete.rs

@@ -464,3 +464,39 @@ fn add_and_delete_single_key_preserves_file() {
         hash2
     );
 }
+
+#[test]
+fn add_key_to_file_without_trailing_newline() {
+    use std::io::Write;
+    let mut tmp = NamedTempFile::new().unwrap();
+    tmp.write_all(b"FOO=bar").unwrap(); // deliberately no trailing newline
+    tmp.flush().unwrap();
+
+    bin()
+        .arg("BAZ")
+        .arg("--set")
+        .arg("qux")
+        .arg("--file")
+        .arg(tmp.path())
+        .assert()
+        .success();
+
+    // Both keys must be readable and intact.
+    bin()
+        .arg("FOO")
+        .arg("--file")
+        .arg(tmp.path())
+        .assert()
+        .success()
+        .stdout("bar\n");
+    bin()
+        .arg("BAZ")
+        .arg("--file")
+        .arg(tmp.path())
+        .assert()
+        .success()
+        .stdout("qux\n");
+
+    let content = fs::read_to_string(tmp.path()).unwrap();
+    assert_eq!(content, "FOO=bar\nBAZ=qux\n");
+}