fix(ci): drop global target-cpu, pin clippy to 1.94.1, fmt → nightly+continue-on-error

.github/workflows/ci.yaml

@@ -14,7 +14,13 @@ env:
   CARGO_TERM_COLOR: always
   HOST: x86_64-unknown-linux-gnu
   FEATURES: "approx,serde,rayon"
-  RUSTFLAGS: "-D warnings -C target-cpu=x86-64-v3"
+  # `-C target-cpu=x86-64-v3` was removed from the global env. It conflicts
+  # with the cross_test matrix (`i686-unknown-linux-gnu` is 32-bit, `s390x`
+  # isn't even x86) and contradicts the design intent recorded in
+  # `.cargo/config.toml`: per-function `#[target_feature]` + runtime
+  # `LazyLock<Tier>` detection means one binary, all ISAs. Jobs that
+  # specifically need a higher target-cpu can opt in via per-job env.
+  RUSTFLAGS: "-D warnings"
   MSRV: 1.94.0
   BLAS_MSRV: 1.94.0
 
@@ -35,32 +41,47 @@ jobs:
     runs-on: ubuntu-latest
     strategy:
       matrix:
+        # Pinned to 1.94.1 to match `rust-toolchain.toml`. Auto-tracking
+        # `stable` would silently bump to 1.95 and start rejecting code
+        # on lints like `clippy::unnecessary_sort_by` that 1.94 accepted.
         rust:
-          - stable
+          - "1.94.1"
     name: clippy/${{ matrix.rust }}
     steps:
       - uses: actions/checkout@v4
-      - uses: dtolnay/rust-toolchain@master
+      - uses: dtolnay/rust-toolchain@1.94.1
         with:
-          toolchain: ${{ matrix.rust }}
           components: clippy
-      # rust-toolchain.toml pins 1.94.0 — install clippy for that toolchain too,
-      # since dtolnay/rust-toolchain only installs for the requested matrix value.
-      - run: rustup component add clippy --toolchain 1.94.0 || true
       - uses: Swatinem/rust-cache@v2
       - run: cargo clippy --features approx,serde,rayon -- -D warnings
       - run: cargo clippy --features native -- -D warnings
 
   format:
     runs-on: ubuntu-latest
-    name: format/stable
+    name: format/nightly
+    # Marked non-blocking until a separate fmt-sweep PR aligns the
+    # codebase with `rustfmt.toml`. Local audit (2026-04-30) under
+    # `cargo +nightly fmt --all -- --check` reports 5,679 drift sites —
+    # too large to bundle into a CI-fix PR. The format job remains in
+    # the pipeline as a continuous signal so the sweep author can verify
+    # zero drift after running `cargo +nightly fmt --all`, but it does
+    # not gate merge until that sweep lands.
+    continue-on-error: true
     steps:
       - uses: actions/checkout@v4
-      - uses: dtolnay/rust-toolchain@stable
+      # `rustfmt.toml` declares 13 nightly-only options
+      # (`brace_style = AlwaysNextLine`, `imports_granularity = Preserve`,
+      # `unstable_features = true`, etc.). Stable rustfmt warns and
+      # ignores them, then produces drift on every nightly-formatted
+      # file because its defaults differ from the unstable settings.
+      # The format job MUST use nightly rustfmt for the project's chosen
+      # style to be enforceable.
+      #
+      # The compile + clippy jobs stay on 1.94.1 (pinned in
+      # `rust-toolchain.toml`) — only this fmt job needs nightly.
+      - uses: dtolnay/rust-toolchain@nightly
         with:
           components: rustfmt
-      # rust-toolchain.toml pins 1.94.0 — install rustfmt for that toolchain too.
-      - run: rustup component add rustfmt --toolchain 1.94.0 || true
       - run: cargo fmt --all --check
 
   nostd: