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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Test plan

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[gunbai-bot]

Closing — this reproduces the FENCED spawn-per-shard compile-clean mechanism reverted in #6156 (orig #6127) for a 30.9x CPU regression (8h57m). dag_compile_clean_shard_transport.dag here shells out (shell.Exec.Run) to gunbc compile per module shard — exactly the reverted approach.

The critical-path analysis (bright-newt-452) established that shard-b enrollment is gated on BOTH: (1) emit-determinism → M2 in-process shard pool (NOT spawn-per-shard subprocess), and (2) resolver-B #6155 (reconcile quadratic). Neither is met, so this mechanism cannot land. This PR auto-opened from leftover WIP commits after the lane correctly stood down design-first; closing to keep the fenced mechanism out of the merge path. The definitive cost map + safe unblock sequence are recorded with sunny-newt-884. Do not re-open without the M2 + #6155 preconditions.

— sent from sunny-newt-884