feat: range aware file write

api_changes/update_260424_next_stable_chunk_boundary.md

@@ -1,15 +1,17 @@
 This update adds a new public deduplication helper for computing restart-safe chunk boundaries from existing chunk boundary metadata.
 
 What changed
-- Added `xet_data::deduplication::next_stable_chunk_boundary(starting_position, chunk_boundaries) -> Option<usize>`.
-- Re-exported it from `xet_data::deduplication` so downstream crates can use it directly.
+- Added `next_stable_chunk_boundary(starting_position, chunk_boundaries) -> Option<usize>`.
+- Canonical implementation lives in `xet_core_structures::xorb_object::constants` (alongside the chunk-size constants it uses).
+- Re-exported from `xet_data::deduplication` for convenience.
 - The function scans forward from `starting_position` and returns the next chunk boundary that satisfies the stable-boundary condition:
   - two consecutive chunk sizes in `[2 * min_chunk, max_chunk - min_chunk)`,
   - where `min_chunk` and `max_chunk` are derived from chunking constants.
 
 Why this matters
 - Callers that already have chunk-boundary metadata can locate a stable resume boundary without re-reading file bytes.
 - This enables deterministic alignment behavior for resumed/partial workflows that need chunk boundaries robust to prefix changes.
+- The server-side `build_file_chunk_hashes_response` now extends dirty ranges to stable chunk boundaries before building windows, so that the client's rechunking around each dirty window is guaranteed to converge to the same chunk boundaries as the original file.
 
 Usage notes
 - `chunk_boundaries` should be monotonically increasing chunk-end offsets produced by the same chunking configuration.

wasm/hf_xet_wasm/src/wasm_file_cleaner.rs

@@ -184,7 +184,8 @@ impl SingleFileCleaner {
         let metadata_ext = FileMetadataExt::new(sha256);
 
         // Now finish the deduplication process.
-        let (file_hash, remaining_file_data, deduplication_metrics) = self.dedup_manager.finalize(Some(metadata_ext));
+        let (file_hash, _chunk_hashes, remaining_file_data, deduplication_metrics) =
+            self.dedup_manager.finalize(Some(metadata_ext));
 
         // Let's check some things that should be invariants
         {