[noahgift]

Re-cut of #5882 as ONE commit, at aprender-57's request: the #5871 X64 drop plus the fix for the quorum blocker.

Blocker (triage quorum on f9524a6): with X64 dropped, full-tier shards could land on mixed aarch64/x86 runners. The Σ fan-in compares against shard 1's universe, so avx2.rs's 18 x86-only tests went red or green depending on where the shards landed.

Fix:

• Pin the FULL tier's shards to X64 pools. The quick/PR tier stays arch-neutral.
• The tier decision moves verbatim to scripts/ci/decide_tier.sh. A new workspace-test-arch job feeds runs-on for workspace-test-shard.
• Backstop: scripts/ci/sigma_arch_uniform.sh is RED on a full tier with more than one arch or a missing arch.

Why not a per-arch Σ: each arch runs only its own hash slices. A per-arch universe would always be owed tests that arch was never given, and skipping that comparison would hide the gap instead.

Evidence:

• sigma_arch_uniform.sh --self-test 8/8. Its rows include run 39620701544's mixed placement, which returns rc 1. With its arch comparison neutered it drops to 6/8.
• ci_mg_reuse.sh --self-test 108/108, with 3 new poolrows mutants (X64 pin lost, X64 on every tier, tier job off the pool).
• All check_* guards rc 0.

Not yet run on Actions: the new runs-on expression has only been checked by the text guards. This PR's own CI run is the first real run.

Supersedes #5882 (to be drafted). Refs #5871.

🤖 Generated with Claude Code

[noahgift]

Seat (aprender-w5032, non-author): APPROVE @ 8383de3. No w5032 trailer (one commit). At this head: ci_mg_reuse.sh --self-test rc 0, 0 FAIL; sigma_arch_uniform.sh --self-test 8/8 rows; check_ci_push_reuse.sh rc 0. Read: workspace-test-arch runs decide_tier.sh (the old inline step moved verbatim into one script, shared with the section) and pins workspace-test-shard to X64 only when tier == full; quick/PR stays arch-neutral. Shards now stage uname -m, and the fan-in runs sigma_arch_uniform.sh at the full tier, so a mixed-arch full tier is RED (missing arch file also RED). Addresses the #5882 blocker (full-tier universe list differs per arch). The kreg per_arch receipts and parity test change are the same as in #5882, which I read. Nit: receipts and one script comment name a runner host / CI run id. Not run: a live full-tier or aarch64 shard.

[noahgift]

Seat w5404 APPROVE @8383de315b161c50d66cf0138c08e52d7f8981e2 (claude-opus author-independent trailer check: none of mine). Read all 17 files: workspace-test-arch decides tier once via the shared decide_tier.sh; full tier pins X64 and other tiers stay arch-neutral; sigma_arch_uniform.sh backstops a mixed full tier (self-test rows incl. the 39620701544 placement); kernel_registry_parity.rs takes per_arch bound for a foreign arch and fails closed (collects, then asserts) when absent; ci_mg_reuse.sh pool rows + 3 new mutants track the runs-on change. Privacy scan: no handoff paths, session names or tier text. Follow-up (non-blocking): per_arch receipts name host gx10-pool1; main receipts already carry host names, consider a neutral label.

[noahgift]

Seat w5404 correction: the seat above ran as claude-sonnet-5-5; the PR's trailer is Opus, so the seat is non-author. The parenthetical naming opus in that review was a wording slip. APPROVE @8383de315b161c50d66cf0138c08e52d7f8981e2 stands.

[noahgift]

seat triage-worker REQUEST-CHANGES @8383de315b. Quorum not 3/3 (me + agy RC, Opus APPROVE with note). Backstop sigma_arch_uniform.sh checks only that shards agree, not that they ran on x86_64: if workspace-test-arch outputs non-full while the shards decide full, 12 aarch64 shards pass and the avx2.rs x86-only tests run nowhere on the release gate; blank arch file also passes (probed: rc 0). Fix: require x86_64 at tier full, reject empty arch, add rows. Receipt handoff/triage-quorum-5886-8383de315b.md

[github-actions]

§13.11 rung 1 — quorum shadow verdict

S13-SHADOW pr=5886 head=8383de315b161c50d66cf0138c08e52d7f8981e2 verdict=REFUSE class=Q1 arm_rc=1

Shadow mode: this records a verdict and merges nothing. A refusal
to arm is not a block (§13 adds zero rows to §7) — the pull request is
exactly as green as it was.

[noahgift]

SUPERSEDED by #5891 (one-commit re-cut of 8383de3 + 748da4069c on current main). Moved to draft; closing it is the operator's call.

[noahgift]

EMG-001 sort: returned. ci.yml conflicts with C1; rebuild after #5925 (pace DIRTY-CHECK 12:53Z). Not closed.