## Why
Blocking rollout reads can continue decompressing and scanning history after the calling async task is dropped.
## What changed
Propagate caller cancellation through rollout readers, prefix validation, model-context scans, history materialization, and working-directory lookup. Check cancellation during compressed input and output, bounded reads, seeks, and between history records. Return an error on cancellation so partial history cannot be mistaken for a complete read.
## Testing
Add regression coverage for dropping a caller during decompression, cancelling compressed input and output (including skippable frames), cancelling reads and seeks on plain and decoded snapshots, and cancelling history materialization between records.
GitOrigin-RevId: e3dac952789b53402f2a5f17c2a2232506feb9d6
## Why
Rollout compression skips files that participate in paginated fork lineages because lineage readers rely on byte offsets into the original JSONL. This prevents shared rollout history from being compressed.
## What changed
- Add a seekable rollout reader that preserves logical JSONL offsets for plain and zstd-compressed files without materializing compressed data beside the rollout.
- Use the reader for lineage validation, model-context replay, and SQLite history projection, including when compression races with a read.
- Add the opt-in `local_thread_store_shared_compression` feature. The default mode continues to leave shared lineages uncompressed for compatibility, while the new mode includes referenced sources and fork pointers.
- Record the uncompressed size in new zstd frames so common prefix-bound checks can avoid decoding the full file.
## Testing
Add coverage for seekable compressed reads, prefix validation across zstd frame shapes, compressed lineage replay and projection, concurrent forks, and compression-mode behavior.
GitOrigin-RevId: 83e519f7eabf7448977eff37c55899858cc17a07
jif