REX-01: executor issues: file infra forjar declarations per host + paiml-implement 4th shadow lane issue

[noahgift]

owner: rex
Epic: #4354 (REX-001). Spec: docs/specifications/review-experiment-protocol.md §7 row REX-01.

Done when (all must hold): infra issue (intel, lambda-labs CPU only, gx10 priority 1, mini: exact apr tag, weights by path+sha256, apr serve unit w/ cgroup budget + health, exec_sha256, train-active yield, intel concurrency group) and paiml-implement issue (quorum.lane_models shadow lane, ARB-APR-001 gx10 revision) filed with checkable acceptance criteria; URLs recorded; Phase-0 check of existing declared labels receipted

Binding: §6 R-1..R-12, §8 STOPs. Ticket id = PMAT-.

[noahgift]

Filed: paiml/infra#1088 (forjar executors, checkable AC) · paiml/paiml-implement#411 comment (4th shadow lane + ARB-APR-001 gx10 revision). Receipt: docs/audits/rex-001/rex-01-receipt.md on rex/001.

[noahgift]

Folded into #4431 (the replacement for #4317, which carried this work). Closing here; the work lands with #4431.