chore: establish development baseline

crates/bat-cas-engine/src/error.rs

@@ -0,0 +1,35 @@
+//! CAS Engine 错误类型定义
+
+use thiserror::Error;
+
+/// CAS Engine 错误类型
+#[derive(Error, Debug)]
+pub enum CasError {
+    /// IO 错误
+    #[error("IO error: {0}")]
+    Io(#[from] std::io::Error),
+
+    /// Hash 不匹配
+    #[error("Hash mismatch: expected {expected}, got {actual}")]
+    HashMismatch {
+        /// 期望的 Hash
+        expected: String,
+        /// 实际的 Hash
+        actual: String,
+    },
+
+    /// 对象不存在
+    #[error("Object not found: {0}")]
+    ObjectNotFound(String),
+
+    /// 数据库错误
+    #[error("Database error: {0}")]
+    Database(String),
+
+    /// 其他错误
+    #[error(transparent)]
+    Other(#[from] anyhow::Error),
+}
+
+/// CAS Engine Result 类型
+pub type Result<T> = std::result::Result<T, CasError>;