LocalWalSyncImpl._flush - Out of Memory crash

[aaravgarg]

Summary

• Fix OOM crash by writing WAL frames incrementally using IOSink instead of building entire data list in memory
• Fix "Cannot add to unmodifiable list" crash by initializing _wals as mutable [] instead of const []
• Free in-memory WAL data after flushing to disk to reduce memory pressure
• Gracefully skip WALs with unavailable file paths instead of throwing

Crash Stats (combined iOS + Android)

• OOM Events: 21 (iOS)
• OOM Users affected: 7 (iOS)
• Unmodifiable list Events: 889 (Android)
• Unmodifiable list Users affected: 6 (Android)
• Crashlytics (iOS OOM): View in Console
• Crashlytics (Android unmodifiable list): View in Console

Test plan

• Verify WAL flushing still works correctly
• Test with large WAL data (should not OOM)
• Verify _wals list operations work (add, remove, etc.)

🤖 Generated with Claude Code

[gemini-code-assist]

Code Review

This pull request effectively addresses a critical Out of Memory (OOM) crash during WAL flushing by switching to an incremental write approach using IOSink. The changes also fix a crash related to modifying an unmodifiable list and gracefully handle cases where a WAL file path is unavailable. Additionally, a subtle but critical bug involving loop variable shadowing has been resolved. The memory footprint is further reduced by clearing WAL data after it's been flushed to disk. The overall solution is robust and well-implemented. I've added one suggestion to further optimize the file writing logic for better performance and readability.

[gemini-code-assist]

This block manually copies bytes from frame into a new ByteData buffer. Since wal.data likely contains Uint8List instances from the byte stream, frame (which is a sublist of an element from wal.data) is also a Uint8List. You can add it to the sink directly, which is more efficient and readable, avoiding the unnecessary allocation and byte-by-byte copy.

            sink.add(Uint32List.fromList([frame.length]).buffer.asUint8List());
            sink.add(frame);