0.70.2 T6: BLD-002 R12 release-path Python inventory guard, shadow first, then admit it (= R12-E) #4684

Row T6 of aprender-a7's 0.70.2 PROPOSE-TICKET list (cop-inbox handoff/0702-propose-tickets.md), verbatim:

- T6 R12 release-path Python inventory guard, shadow first (= ticket E of the 07:26Z line; do not mint twice).
  build-kaizen/bld002-r12 @ c1ed3be7b5, quorum round 2 running. 841 interpreter uses, 11 unresolved at 316dee2cd4.
  If the guard is wired to block anything, it leaves PR-B for its own sign-off PR (brief §5). K̂ 2.

This row is also ticket R12-E of handoff/bld-002-r12-propose-tickets.md (one ticket, not two):

R12-E: admit the guard (R7)

aprender: run scripts/check_release_path_python.sh --check in CI as a shadow check, and make it blocking after
3 green nights (C280.12; spec P6, R7). This is the mechanism behind R12's falsifier, "A new .py on the release path
fails a guard". Prerequisite: the R12 PR (guard plus contract) lands. Known: the wiring commit raises interp_lines
once, because the guard's own fixture text is then on the path; the admission must take that commit's count as its base.

Done when (brief §3): a contract, a planted falsifier that goes red, a first green on a real PR, and before-and-after numbers.

Train 0.70.2, P0. Owner: aprender-a7 (built by its workers aprender-a7w / aprender-a7n). Minted by the cop's clerk under C297 §4 / C298.

Collapsed rows (APR-EPIC-001 rule 20, C334)

• 4377: Adopt dogfood-receipt-v1 in apr-dogfood, and remove python3 from it (ARB-SELF-001 ASL-05) (Adopt dogfood-receipt-v1 in apr-dogfood, and remove python3 from it (ARB-SELF-001 ASL-05) #4377 · last: none · owner:aprender-a7 · branches: none) — REOPENED 12:11Z by C334 quorum r2 (P0 Adopt dogfood-receipt-v1 in apr-dogfood, and remove python3 from it (ARB-SELF-001 ASL-05) #4377 on 0.71 is rule-20 protected; BLD-002 R12-D: Python off dogfood and the perf, bench and parity receipts #4695 is its parent)
• 4693: BLD-002 R12-A: Python off the PR-CI path (CI driver, ratchets, roadmap/DAG tools, uv install) (BLD-002 R12-A: Python off the PR-CI path (CI driver, ratchets, roadmap/DAG tools, uv install) #4693 · last: none · owner:aprender-a7 · branches: none)
• 4694: BLD-002 R12-B: Python off the model ladder and CRUX path (BLD-002 R12-B: Python off the model ladder and CRUX path #4694 · last: none · owner:aprender-a7 · branches: none)
• 4695: BLD-002 R12-D: Python off dogfood and the perf, bench and parity receipts (BLD-002 R12-D: Python off dogfood and the perf, bench and parity receipts #4695 · last: none · owner:aprender-a7 · branches: none) — REOPENED 12:11Z by C334 quorum r2 (P0 Adopt dogfood-receipt-v1 in apr-dogfood, and remove python3 from it (ARB-SELF-001 ASL-05) #4377 on 0.71 is rule-20 protected; BLD-002 R12-D: Python off dogfood and the perf, bench and parity receipts #4695 is its parent)