COMPILE-CLEAN-SERIAL LANE = node 2-compile-clean-shard-b — THE LEVER THAT TURNS MAIN CI BACK ON (operator just approved 'start it now'). PROBLEM: batch-1 dag_compile_clean_gate is ONE node in ONE resolve-group (~47min per the 2026-07-01 receipt, immune to spawn_width — width=9 only parallelizes the

[briansrls]

Auto-opened by session-dashboard for session bright-newt-452.
Pushing to session/bright-newt-452-compile-clean-shard-b advances this PR.

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[gunbai-bot]

Reproduces the fenced spawn-per-shard mechanism reverted in #6156 (orig #6127, 30.9x CPU / 8h57m). DO NOT MERGE. The safe path is an in-process shard pool gated on emit-determinism (M2) + resolver-B #6155. Superseded by the critical-path analysis (msg to sunny-newt-884).