refactor(server): move region files to 3D (rx, ry, rz) grid

crates/server/src/save/region_actor.rs

@@ -73,7 +73,7 @@ impl SaveActor {
 /// The actor's run loop: it owns the region-file map and answers requests until every sender is dropped.
 fn actor_loop(region_dir: &Path, request_rx: &Receiver<SaveRequest>) {
     // The actor is the sole owner of this map, so region files need no lock of their own.
-    let mut regions: HashMap<(i32, i32), RegionFile> = HashMap::new();
+    let mut regions: HashMap<(i32, i32, i32), RegionFile> = HashMap::new();
     while let Ok(request) = request_rx.recv() {
         match request {
             SaveRequest::Read { pos, reply } => {
@@ -112,7 +112,7 @@ fn actor_loop(region_dir: &Path, request_rx: &Receiver<SaveRequest>) {
 /// # Errors
 ///
 /// Returns the first [`SaveError`] produced by [`RegionFile::save`]; remaining dirty regions are still flushed.
-fn flush_dirty(regions: &mut HashMap<(i32, i32), RegionFile>) -> Result<(), SaveError> {
+fn flush_dirty(regions: &mut HashMap<(i32, i32, i32), RegionFile>) -> Result<(), SaveError> {
     let mut result = Ok(());
     for region in regions.values_mut() {
         // Clean regions are skipped so a flush never rewrites an unchanged file.
@@ -136,17 +136,17 @@ fn flush_dirty(regions: &mut HashMap<(i32, i32), RegionFile>) -> Result<(), Save
 ///
 /// Returns a [`SaveError`] from [`RegionFile::open`] if the region file exists but cannot be read or decoded.
 fn region_mut<'a>(
-    regions: &'a mut HashMap<(i32, i32), RegionFile>,
+    regions: &'a mut HashMap<(i32, i32, i32), RegionFile>,
     region_dir: &Path,
     pos: ChunkPos,
 ) -> Result<&'a mut RegionFile, SaveError> {
-    let key = region_coords(pos.x, pos.z);
+    let key = region_coords(pos.x, pos.y, pos.z);
     // The region file is opened once on first touch; every later access hits the in-memory copy.
     match regions.entry(key) {
         Entry::Occupied(entry) => Ok(entry.into_mut()),
-        Entry::Vacant(entry) => {
-            Ok(entry.insert(RegionFile::open(region_path(region_dir, pos.x, pos.z))?))
-        }
+        Entry::Vacant(entry) => Ok(entry.insert(RegionFile::open(region_path(
+            region_dir, pos.x, pos.y, pos.z,
+        ))?)),
     }
 }
 
@@ -156,7 +156,7 @@ fn region_mut<'a>(
 ///
 /// Returns a [`SaveError`] if the region file cannot be opened or the stored record cannot be decoded.
 fn read_chunk(
-    regions: &mut HashMap<(i32, i32), RegionFile>,
+    regions: &mut HashMap<(i32, i32, i32), RegionFile>,
     region_dir: &Path,
     pos: ChunkPos,
 ) -> Result<Option<ChunkData>, SaveError> {

crates/server/src/save/region_file.rs

@@ -13,20 +13,26 @@ use shared::save::record;
 use shared::save::region::{HeaderEntry, RegionIndex};
 use shared::world::{ChunkData, ChunkPos};
 
-/// The side length, in chunk columns, of the square footprint one region file covers.
+/// The side length, in chunks, of the cube one region file covers on every axis.
 pub const REGION_SIZE: i32 = 32;
 
-/// Maps a chunk column `(cx, cz)` to the coordinates `(rx, rz)` of the region that contains it.
+/// Maps a chunk `(cx, cy, cz)` to the coordinates `(rx, ry, rz)` of the region cube that contains it.
+///
+/// Every axis is floored via `div_euclid` (not truncating division) so negative chunk coordinates map to the region below rather than toward zero: chunk `-1` belongs to region `-1`, not region `0`.
 #[must_use]
-pub fn region_coords(cx: i32, cz: i32) -> (i32, i32) {
-    (cx.div_euclid(REGION_SIZE), cz.div_euclid(REGION_SIZE))
+pub fn region_coords(cx: i32, cy: i32, cz: i32) -> (i32, i32, i32) {
+    (
+        cx.div_euclid(REGION_SIZE),
+        cy.div_euclid(REGION_SIZE),
+        cz.div_euclid(REGION_SIZE),
+    )
 }
 
-/// Builds the on-disk path of the region file containing chunk column `(cx, cz)` within `dir`.
+/// Builds the on-disk path of the region file containing chunk `(cx, cy, cz)` within `dir`.
 #[must_use]
-pub fn region_path(dir: &Path, cx: i32, cz: i32) -> PathBuf {
-    let (rx, rz) = region_coords(cx, cz);
-    dir.join(format!("r.{rx}.{rz}.region"))
+pub fn region_path(dir: &Path, cx: i32, cy: i32, cz: i32) -> PathBuf {
+    let (rx, ry, rz) = region_coords(cx, cy, cz);
+    dir.join(format!("r.{rx}.{ry}.{rz}.region"))
 }
 
 /// An open region file: its `SYNR` index, the resident chunk records, and its on-disk location.

crates/server/src/tests/region_file.rs

@@ -13,27 +13,27 @@ fn sample(pos: ChunkPos) -> ChunkData {
 }
 
 #[test]
-fn region_coords_floor_negative_columns() {
-    // Truncating division would map -1 to region 0; Euclidean flooring maps it to region -1.
-    assert_eq!(region_coords(0, 0), (0, 0));
-    assert_eq!(region_coords(31, 31), (0, 0));
-    assert_eq!(region_coords(-1, -1), (-1, -1));
-    assert_eq!(region_coords(-32, -33), (-1, -2));
+fn region_coords_floor_negative_chunks() {
+    // Truncating division would map -1 to region 0; Euclidean flooring maps it to region -1. Every axis, including Y, floors identically under the 3D region grid.
+    assert_eq!(region_coords(0, 0, 0), (0, 0, 0));
+    assert_eq!(region_coords(31, 31, 31), (0, 0, 0));
+    assert_eq!(region_coords(-1, -1, -1), (-1, -1, -1));
+    assert_eq!(region_coords(-32, -33, 64), (-1, -2, 2));
 }
 
 #[test]
 fn region_path_names_the_region_file() {
     let dir = Path::new("/saves/world/region");
     assert_eq!(
-        region_path(dir, -1, 5),
-        Path::new("/saves/world/region/r.-1.0.region")
+        region_path(dir, -1, 40, 5),
+        Path::new("/saves/world/region/r.-1.1.0.region")
     );
 }
 
 #[test]
 fn open_missing_file_is_empty() -> Result<(), SaveError> {
     let dir = tempfile::tempdir()?;
-    let region = RegionFile::open(dir.path().join("r.0.0.region"))?;
+    let region = RegionFile::open(dir.path().join("r.0.0.0.region"))?;
     assert!(region.is_empty());
     assert_eq!(region.read_chunk(ChunkPos::new(0, 0, 0))?, None);
     Ok(())
@@ -42,7 +42,7 @@ fn open_missing_file_is_empty() -> Result<(), SaveError> {
 #[test]
 fn round_trips_chunks_through_disk() -> Result<(), SaveError> {
     let dir = tempfile::tempdir()?;
-    let path = dir.path().join("r.0.0.region");
+    let path = dir.path().join("r.0.0.0.region");
 
     let positions = [
         ChunkPos::new(0, 0, 0),
@@ -72,7 +72,7 @@ fn round_trips_chunks_through_disk() -> Result<(), SaveError> {
 #[test]
 fn record_offsets_are_valid_and_contiguous() -> Result<(), SaveError> {
     let dir = tempfile::tempdir()?;
-    let path = dir.path().join("r.0.0.region");
+    let path = dir.path().join("r.0.0.0.region");
 
     let mut region = RegionFile::open(path.clone())?;
     for pos in [
@@ -99,7 +99,7 @@ fn record_offsets_are_valid_and_contiguous() -> Result<(), SaveError> {
 #[test]
 fn remove_drops_only_the_named_chunk() -> Result<(), SaveError> {
     let dir = tempfile::tempdir()?;
-    let path = dir.path().join("r.0.0.region");
+    let path = dir.path().join("r.0.0.0.region");
     let kept = ChunkPos::new(0, 0, 0);
     let dropped = ChunkPos::new(1, 1, 1);
 
@@ -121,7 +121,7 @@ fn remove_drops_only_the_named_chunk() -> Result<(), SaveError> {
 #[test]
 fn stray_tmp_file_does_not_corrupt_reads() -> Result<(), SaveError> {
     let dir = tempfile::tempdir()?;
-    let path = dir.path().join("r.0.0.region");
+    let path = dir.path().join("r.0.0.0.region");
     let pos = ChunkPos::new(0, 0, 0);
 
     let mut region = RegionFile::open(path.clone())?;
@@ -129,7 +129,7 @@ fn stray_tmp_file_does_not_corrupt_reads() -> Result<(), SaveError> {
     region.save()?;
 
     // A leftover .tmp from an interrupted save must be ignored: only the renamed target is read.
-    fs::write(dir.path().join("r.0.0.region.tmp"), b"garbage")?;
+    fs::write(dir.path().join("r.0.0.0.region.tmp"), b"garbage")?;
     let reopened = RegionFile::open(path)?;
     assert_eq!(reopened.read_chunk(pos)?, Some(sample(pos)));
     Ok(())

crates/server/src/tests/world_server.rs

@@ -108,7 +108,7 @@ fn saved_modification_is_applied_over_baseline() -> Result<(), SaveError> {
     let mut data = ChunkData::new(pos, 0);
     data.set(edited_index, edited_block);
 
-    let mut region = RegionFile::open(region_path(dir.path(), pos.x, pos.z))?;
+    let mut region = RegionFile::open(region_path(dir.path(), pos.x, pos.y, pos.z))?;
     region.write_chunk(pos, &data, 0)?;
     region.save()?;
 
@@ -180,7 +180,7 @@ fn clean_chunk_is_not_written_back_on_eviction() -> Result<(), SaveError> {
     flush(&world)?;
 
     // No record may exist for a chunk that never diverged from its baseline.
-    let region = RegionFile::open(region_path(dir.path(), pos.x, pos.z))?;
+    let region = RegionFile::open(region_path(dir.path(), pos.x, pos.y, pos.z))?;
     assert!(region.read_chunk(pos)?.is_none());
     Ok(())
 }