test: enforce AppResult alias usage

src/lib.rs

@@ -10,7 +10,7 @@
 //! - [`AppError`] — thin wrapper around a semantic error kind and optional
 //!   message
 //! - [`AppErrorKind`] — stable internal taxonomy of application errors
-//! - [`AppResult`] — convenience result alias (defaults to [`AppError`])
+//! - [`AppResult`] — convenience alias for returning [`AppError`]
 //! - [`ErrorResponse`] — stable wire-level JSON payload for HTTP APIs
 //! - [`AppCode`] — public, machine-readable error code for clients
 //!

tests/enforce_app_result_alias.rs

@@ -0,0 +1,53 @@
+use std::{
+    ffi::OsStr,
+    fs, io,
+    path::{Path, PathBuf}
+};
+
+fn collect_rs_files(dir: &Path, files: &mut Vec<PathBuf>) -> io::Result<()> {
+    for entry in fs::read_dir(dir)? {
+        let entry = entry?;
+        let path = entry.path();
+        if path.is_dir() {
+            collect_rs_files(&path, files)?;
+        } else if path.extension() == Some(OsStr::new("rs")) {
+            files.push(path);
+        }
+    }
+    Ok(())
+}
+
+#[test]
+fn prohibits_direct_result_app_error_usage() {
+    let src_dir = PathBuf::from(env!("CARGO_MANIFEST_DIR")).join("src");
+    let mut files = Vec::new();
+    collect_rs_files(&src_dir, &mut files).expect("collect Rust sources");
+
+    let mut offenders = Vec::new();
+
+    for path in &files {
+        let content = fs::read_to_string(path)
+            .unwrap_or_else(|err| panic!("failed to read {}: {err}", path.display()));
+
+        for (idx, line) in content.lines().enumerate() {
+            if line.contains("Result<")
+                && line.contains("AppError")
+                && !line.contains("AppResult<")
+            {
+                if path.file_name() == Some(OsStr::new("app_error.rs"))
+                    && line.contains("pub type AppResult")
+                {
+                    continue;
+                }
+                offenders.push(format!("{}:{}", path.display(), idx + 1));
+            }
+        }
+    }
+
+    if !offenders.is_empty() {
+        panic!(
+            "Found direct `Result<_, AppError>` usage; replace with `AppResult<_>`: {}",
+            offenders.join(", ")
+        );
+    }
+}