refactor: split storage engine into focused submodules

Cargo.toml

@@ -19,6 +19,7 @@ parking_lot = { version = "0.12.4", features = ["send_guard"] }
 fxhash = "0.2.1"
 static_assertions = "1.1.0"
 rayon = "1.10.0"
+thiserror = "2"
 
 [dev-dependencies]
 criterion = "0.6.0"

src/node.rs

@@ -17,6 +17,7 @@ use arrayvec::ArrayVec;
 use proptest::{arbitrary, strategy, strategy::Strategy};
 use proptest_derive::Arbitrary;
 use std::cmp::{max, min};
+use thiserror::Error;
 
 const MAX_PREFIX_LENGTH: usize = 64;
 
@@ -54,10 +55,13 @@ pub enum NodeKind {
     },
 }
 
-#[derive(Debug)]
+#[derive(Debug, Error)]
 pub enum NodeError {
+    #[error("children unsupported")]
     ChildrenUnsupported,
+    #[error("max prefix length exceeded")]
     MaxPrefixLengthExceeded,
+    #[error("no value")]
     NoValue,
 }
 

src/page/manager.rs

@@ -1,22 +1,35 @@
 use crate::page::PageId;
+use thiserror::Error;
 
 pub(super) mod mmap;
 pub(super) mod options;
 
 /// Represents various errors that might arise from page operations.
-#[derive(Debug)]
+#[derive(Debug, Error)]
 pub enum PageError {
+    #[error("page not found: {0}")]
     PageNotFound(PageId),
+    #[error("page occupied: {0}")]
     PageOccupied(PageId),
+    #[error("page dirty: {0}")]
     PageDirty(PageId),
+    #[error("page limit reached")]
     PageLimitReached,
+    #[error("invalid root page: {0}")]
     InvalidRootPage(PageId),
+    #[error("invalid cell pointer")]
     InvalidCellPointer,
+    #[error("no free cells")]
     NoFreeCells,
+    #[error("page is full")]
     PageIsFull,
+    #[error("page split limit reached")]
     PageSplitLimitReached,
-    IO(std::io::Error),
+    #[error("I/O error: {0}")]
+    IO(#[from] std::io::Error),
+    #[error("invalid value")]
     InvalidValue,
+    #[error("invalid page contents: {0}")]
     InvalidPageContents(PageId),
     // TODO: add more errors here for other cases.
 }