⚡📊 pattern filter returns empty on task output containing matches

Bug

When using ⚡📊 with a pattern parameter to grep stored task output, it returns empty results even when the output definitely contains matching lines.

Reproduction

1. Run a cargo build that produces errors: ⚡▶️ ['cargo check --all-features 2>&1']
2. Build fails with 16 errors (confirmed via offset:-100 showing 'due to 16 previous errors')
3. Try to grep: ⚡📊 {'action':'output','task_id':'🛠️33','pattern':'error\\[E','raw':true}
4. Returns empty: {output: '', filtered: true, truncated: true}
5. Also tried: pattern:'error', pattern:'^error' — all return empty or just the summary line

Expected

Pattern filter should return all lines matching the regex from the stored output.

Workaround

Reading with negative offsets in chunks works, but defeats the purpose of the pattern filter.