refactor(server,common): introduce custom error types with thiserror and miette

common/src/error.rs

@@ -0,0 +1,65 @@
+use miette::Diagnostic;
+use thiserror::Error;
+
+/// Result type using the common's custom error type.
+pub type Result<T> = std::result::Result<T, Error>;
+
+#[derive(Debug, Error, Diagnostic)]
+pub enum Error {
+    /// File or network I/O error.
+    #[error(transparent)]
+    #[diagnostic(code(common::io_error))]
+    Io(#[from] std::io::Error),
+
+    #[error(transparent)]
+    #[diagnostic(code(common::rustls_error))]
+    Tls(#[from] rustls::Error),
+
+    /// TOML configuration file parse error.
+    #[error(transparent)]
+    #[diagnostic(code(common::toml_error))]
+    Toml(#[from] toml::de::Error),
+
+    #[error(transparent)]
+    #[diagnostic(code(common::json_error))]
+    Json(#[from] serde_json::Error),
+
+    #[error(transparent)]
+    #[diagnostic(code(common::rcgen_error))]
+    RCGen(#[from] rcgen::Error),
+
+    /// Configuration validation or missing required fields.
+    #[error("Config error: {0}")]
+    #[diagnostic(code(common::config_error))]
+    Config(String),
+
+    /// Invalid key exchange mode string.
+    #[error("Invalid mode: {0}")]
+    #[diagnostic(code(common::invalid_mode))]
+    InvalidMode(String),
+
+    /// Protocol-level error (malformed requests, unexpected responses).
+    #[error("Protocol error: {0}")]
+    #[diagnostic(code(common::protocol_error))]
+    Protocol(String),
+}
+
+impl Error {
+    /// Create an invalid mode error.
+    #[inline]
+    pub fn invalid_mode(error: impl Into<String>) -> Self {
+        Self::InvalidMode(error.into())
+    }
+
+    /// Create a config error.
+    #[inline]
+    pub fn config(error: impl Into<String>) -> Self {
+        Self::Config(error.into())
+    }
+
+    /// Create a protocol error.
+    #[inline]
+    pub fn protocol(error: impl Into<String>) -> Self {
+        Self::Protocol(error.into())
+    }
+}