route heavy work to a second executor

A second high-capability coding agent runs the heavy, self-contained implementation legs — big refactors, multi-file features, long autonomous build loops — while the main session stays free to spec, decompose, review, and verify. The threshold is bright-line: legs over ~50 changed lines or touching two-plus files get delegated by default.

When the orchestrating session also types the implementation, its context fills with diffs and the review gets shallow. A second executor takes the grind; the session that holds the intent stays clear enough to check the work.

The main loop writes the spec, the second executor grinds, and the verify loop never leaves the main session — the diff gets reviewed, the tests get run, the rendered result gets looked at before anything ships. Diagnosis-only passes carry an explicit 'report only, do not edit' fence.

The whole method is downloadable and adaptable — rules/route-heavy-to-codex.md and skills/codex/SKILL.md inside the zip. Any second coding CLI works as the executor; the pattern is the division of labor, not the vendor.