quest: close the parallel-frontend measurement; the queue keeps stable rustc

quest/m0/ci/README.md

@@ -93,6 +93,19 @@ Decided 2026-10-23 (maintainer), to speed up the serial queue: structural
 changes first (concurrent entries, parallel modules, one test build), then a
 measured nightly-compiler experiment.
 
+Measured 2026-11-04, after the landing quest closed: the queue keeps stable
+rustc, without Cranelift (decided 2026-10-27) or the parallel frontend
+([moq-dev/moq#7900](https://github.com/moq-dev/moq/pull/7900)). On the
+queue's test build after a moq-net edit (jobs 8, 12 CPUs, 5 interleaved
+runs each), the pinned nightly's `--jobs-frontend=8` took 15% longer and
+21% more CPU than the same nightly without it, against a 6% A/A spread, and
+did not shorten the critical `moq-net` test unit. moq-dev/rust2's nightly
+benchmark agrees across 8 runs: clean builds 1-7% slower, a hub edit 2-6%
+faster, for 8-15% more CPU. The ceiling is small anyway: the queue's test
+build is 37% of its job time, and cargo runs fewer than 8 units for only
+27% of it. The pinned nightly also fails the gate today, since it deprecates
+`fetch_update` and the gate denies warnings.
+
 Decided 2026-10-15: local CPU admission, test-cost reductions, and setup
 reductions are all m0. `quest gate` owns generic command admission; repositories
 adopt it through their entrypoints. Agents remain concurrent. Selective test
@@ -164,7 +177,6 @@ The historical samples locate candidates; they are not controlled benchmarks.
 - [Read-only pull-request CI](/quest/m0/ci/read-only-secrets.md) - write secrets and publisher identities reach only protected branches and tags, never a pushed branch
 - [A cache error is a miss](/quest/m0/ci/nix-cache-5xx.md) - a transient `nix.moq.dev` 5xx no longer fails `just ci`
 - [Gate each diff in under five minutes](/quest/m0/ci/five-minutes.md) - `just check`, test phases included, finishes within a worker's 5-minute prompt cache, admission wait included
-- [Measure the parallel frontend](/quest/m0/ci/nightly-levers.md) - a pinned nightly's parallel frontend, adopted only if the numbers beat its risks; Cranelift is ruled out
 - [Verify the R2 Rust cache](/quest/m0/ci/mbx-r2-verify.md) - confirm the hosted Nightly jobs reuse the previous Nightly, then measure restore time and expiry
 - [Verify the Nix cache](/quest/m0/ci/nix-cache-verify.md) - confirm releases use `nix.moq.dev`, check its bucket sizes, and retire Cachix
 - [Unify dependency features](/quest/m0/ci/hakari.md) - align the FFI builds' features and record the hosted platform jobs' hits once the workspace-hack lands