Fix Gemini protocol status codes and error handling

- Path security violations now return 51 (Not Found) instead of 59 (Bad Request)
- Timeouts return 41 (Server Unavailable) per Gemini spec
- Add comprehensive request validation: empty requests, oversized requests (>1024 bytes), malformed URLs
- Fix CLI argument conflict (config -c vs cert -c)
- Update documentation with status codes, error handling guidelines, and lint checking
- Add environment setup instructions for clippy and cargo PATH

src/request.rs

@@ -1,6 +1,11 @@
 use path_security::validate_path;
 use std::path::{Path, PathBuf};
 
+#[derive(Debug, PartialEq)]
+pub enum PathResolutionError {
+    NotFound,
+}
+
 pub fn parse_gemini_url(request: &str, expected_host: &str) -> Result<String, ()> {
     if let Some(url) = request.strip_prefix("gemini://") {
         let host_end = url.find('/').unwrap_or(url.len());
@@ -15,7 +20,7 @@ pub fn parse_gemini_url(request: &str, expected_host: &str) -> Result<String, ()
     }
 }
 
-pub fn resolve_file_path(path: &str, dir: &str) -> Result<PathBuf, ()> {
+pub fn resolve_file_path(path: &str, dir: &str) -> Result<PathBuf, PathResolutionError> {
     let file_path_str = if path == "/" {
         "index.gmi".to_string()
     } else if path.ends_with('/') {
@@ -25,8 +30,18 @@ pub fn resolve_file_path(path: &str, dir: &str) -> Result<PathBuf, ()> {
     };
 
     match validate_path(Path::new(&file_path_str), Path::new(dir)) {
-        Ok(safe_path) => Ok(safe_path),
-        Err(_) => Err(()),
+        Ok(safe_path) => {
+            // Path is secure, now check if file exists
+            if safe_path.exists() {
+                Ok(safe_path)
+            } else {
+                Err(PathResolutionError::NotFound)
+            }
+        },
+        Err(_) => {
+            // Path validation failed - treat as not found
+            Err(PathResolutionError::NotFound)
+        },
     }
 }
 
@@ -71,6 +86,8 @@ mod tests {
     #[test]
     fn test_resolve_file_path_root() {
         let temp_dir = TempDir::new().unwrap();
+        // Create index.gmi file since we now check for existence
+        std::fs::write(temp_dir.path().join("index.gmi"), "# Test").unwrap();
         assert!(resolve_file_path("/", temp_dir.path().to_str().unwrap()).is_ok());
     }
 
@@ -78,19 +95,28 @@ mod tests {
     fn test_resolve_file_path_directory() {
         let temp_dir = TempDir::new().unwrap();
         std::fs::create_dir(temp_dir.path().join("test")).unwrap();
+        std::fs::write(temp_dir.path().join("test/index.gmi"), "# Test").unwrap();
         assert!(resolve_file_path("/test/", temp_dir.path().to_str().unwrap()).is_ok());
     }
 
     #[test]
     fn test_resolve_file_path_file() {
         let temp_dir = TempDir::new().unwrap();
+        std::fs::write(temp_dir.path().join("test.gmi"), "# Test").unwrap();
         assert!(resolve_file_path("/test.gmi", temp_dir.path().to_str().unwrap()).is_ok());
     }
 
     #[test]
     fn test_resolve_file_path_traversal() {
         let temp_dir = TempDir::new().unwrap();
-        assert!(resolve_file_path("/../etc/passwd", temp_dir.path().to_str().unwrap()).is_err());
+        assert_eq!(resolve_file_path("/../etc/passwd", temp_dir.path().to_str().unwrap()), Err(PathResolutionError::NotFound));
+    }
+
+    #[test]
+    fn test_resolve_file_path_not_found() {
+        let temp_dir = TempDir::new().unwrap();
+        // Don't create the file, should return NotFound error
+        assert_eq!(resolve_file_path("/nonexistent.gmi", temp_dir.path().to_str().unwrap()), Err(PathResolutionError::NotFound));
     }
 
     #[test]