Replace the per-render readdirSync().filter().map(statSync).sort() chain
with a single-pass max-by-mtime loop. Drops the O(n log n) sort and the
throwaway intermediate array; I/O and resolved-file behavior are identical.
Adds the first behavior-lock test for the todo-resolution path.
The larger disk-backed cache win from the issue is deferred: statusline is
a fresh child process per render, so any cache must be disk-backed with
invalidation/atomic-write design that needs maintainer input.
Co-authored-by: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
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