feat(wave1): App error type and Result alias [claudbg-i09w]

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

.beans/claudbg-i09w--app-error-type-and-result-alias.md

@@ -1,11 +1,12 @@
 ---
 # claudbg-i09w
 title: App error type and Result alias
-status: todo
+status: completed
 type: task
+priority: normal
 created_at: 2026-03-27T19:38:56Z
-updated_at: 2026-03-27T19:38:56Z
+updated_at: 2026-03-28T04:15:59Z
 parent: claudbg-h7xu
 ---
 
-Define a top-level AppError enum (IoError, ParseError, DbError, NotFound, etc.) and a Result<T> alias. Use thiserror or a similar crate.
+Created src/error.rs with AppError enum (Io, Parse, Db, NotFound, InvalidArg) and Result<T> alias using thiserror. All variants have doc comments. Six unit tests verify Display impl for each variant and From<io::Error> conversion. Updated src/lib.rs to declare pub mod error and src/main.rs to import claudbg::error::Result.

src/error.rs

@@ -0,0 +1,73 @@
+//! Application-level error types for claudbg.
+
+/// Application-level error type.
+#[derive(Debug, thiserror::Error)]
+pub enum AppError {
+    /// Wraps [`std::io::Error`] for filesystem and I/O failures.
+    #[error("I/O error: {0}")]
+    Io(#[from] std::io::Error),
+    /// A parsing failure with a descriptive message.
+    #[error("Parse error: {0}")]
+    Parse(String),
+    /// A database operation failure with a descriptive message.
+    #[error("Database error: {0}")]
+    Db(String),
+    /// The requested session or agent ID was not found.
+    #[error("Session not found: {0}")]
+    NotFound(String),
+    /// An invalid argument was supplied by the user.
+    #[error("Invalid argument: {0}")]
+    InvalidArg(String),
+}
+
+/// Convenience `Result` alias using [`AppError`].
+pub type Result<T> = std::result::Result<T, AppError>;
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use std::io;
+
+    /// `AppError::Io` displays the wrapped I/O error message.
+    #[test]
+    fn display_io() {
+        let err = AppError::Io(io::Error::new(io::ErrorKind::NotFound, "file missing"));
+        assert_eq!(err.to_string(), "I/O error: file missing");
+    }
+
+    /// `AppError::Parse` displays the message passed to the constructor.
+    #[test]
+    fn display_parse() {
+        let err = AppError::Parse("bad JSON".to_string());
+        assert_eq!(err.to_string(), "Parse error: bad JSON");
+    }
+
+    /// `AppError::Db` displays the message passed to the constructor.
+    #[test]
+    fn display_db() {
+        let err = AppError::Db("connection refused".to_string());
+        assert_eq!(err.to_string(), "Database error: connection refused");
+    }
+
+    /// `AppError::NotFound` displays the ID that was missing.
+    #[test]
+    fn display_not_found() {
+        let err = AppError::NotFound("abc12345".to_string());
+        assert_eq!(err.to_string(), "Session not found: abc12345");
+    }
+
+    /// `AppError::InvalidArg` displays the invalid argument description.
+    #[test]
+    fn display_invalid_arg() {
+        let err = AppError::InvalidArg("unknown token: foo".to_string());
+        assert_eq!(err.to_string(), "Invalid argument: unknown token: foo");
+    }
+
+    /// `AppError::Io` can be constructed via `From<io::Error>`.
+    #[test]
+    fn from_io_error() {
+        let io_err = io::Error::new(io::ErrorKind::PermissionDenied, "denied");
+        let app_err: AppError = io_err.into();
+        assert!(app_err.to_string().contains("denied"));
+    }
+}

src/lib.rs

@@ -3,7 +3,7 @@
 // pub mod cli;
 // pub mod commands;
 // pub mod db;
-// pub mod error;
+pub mod error;
 // pub mod models;
 // pub mod output;
 // pub mod util;

src/main.rs

@@ -1,3 +1,8 @@
+//! claudbg binary entry point.
+
+use claudbg::error::Result;
+
 fn main() {
+    let _: Result<()> = Ok(());
     println!("Hello, world!");
 }