## What changed
Move full rollout history reading and parsing into one blocking worker for both plain `.jsonl` and compressed `.jsonl.zst` files. Use the shared cancellation-aware line iterator so canceled loads stop before processing another record, while preserving rollout items, thread IDs, and parse-error counts.
## Testing
Add regression tests for cancellation between records and equivalent history-loading results across plain and compressed files, including Unicode, CRLF line endings, malformed records, empty files, and invalid UTF-8.
GitOrigin-RevId: 65e1bd7ebcdbbd0ab5f560e73b2c7f074f627f8f
## Why
Compressed snippet searches schedule a blocking task for every line read. Keeping the scan on one worker avoids repeated task scheduling.
## What changed
Use `RolloutLineReader::find_map` to scan compressed rollouts on a single blocking worker, stopping at the first matching snippet. Preserve read metrics and stop delivering records when the search is canceled, including cancellation during a read.
## Testing
Add tests for first-match snippets, case-insensitive literal matching, malformed records, missing matches, stream errors before a match, and cancellation between lines or during a read.
GitOrigin-RevId: 295206b1a00e861bc44606bd843f6ed8c3e6aae1
Charlie Marsh