chore: fix wasm builds

.github/workflows/ci.yml

@@ -81,6 +81,14 @@ jobs:
           test "$(node -p 'process.versions.node.split(".")[0]')" = "$NODE_VERSION"
           wasm-pack --version
           node --version
+          # wasm-pack uses the shell's wasm-bindgen only at Cargo.lock's exact
+          # version; otherwise it cargo-installs one (71s) — so a lock bump
+          # must move flake.nix's wasmBindgenCli too, and this says so.
+          lock="$(awk '/^name = "wasm-bindgen"$/ {getline; gsub(/[^0-9.]/, ""); print}' Cargo.lock)"
+          test "$(wasm-bindgen --version)" = "wasm-bindgen $lock" || {
+            echo "flake.nix wasmBindgenCli is $(wasm-bindgen --version); Cargo.lock wants $lock" >&2
+            exit 1
+          }
 
       # The same script a developer runs locally, so there is one answer to
       # "how is the bundle built" rather than two that can drift. It builds all
@@ -157,29 +165,21 @@ jobs:
       - name: Every check job gates the deploy
         run: python3 scripts/check-ci-graph.py
 
-  # Too slow on GitHub Actions
-  #
-  # nix-test:
-  #   name: Nix Test
-  #   runs-on: ubuntu-latest
-  #   steps:
-  #     - name: Free up disk space
-  #       run: |
-  #             sudo rm -rf /usr/share/dotnet \
-  #                         /usr/local/lib/android
-  #             sudo df -h
-
-  #     - uses: actions/checkout@v7
-  #     - name: Install Nix
-  #       uses: DeterminateSystems/nix-installer-action@v14
-
-  #     - name: Magic Nix Cache
-  #       uses: DeterminateSystems/magic-nix-cache-action@v8
-
-  #     - name: Check Nix health
-  #       run: nix doctor
-
-  #     - run: nix build
+  # ---------------------------------------------------------------------------
+  # The crate2nix build (Cargo.nix), which `cargo` never exercises. It was off
+  # because GitHub-hosted runners start with an empty store and rebuilt every
+  # dependency crate each run. The NixOS runners substitute from titan's
+  # harmonia first, and titan builds gh/main's `#improvise` hourly, so a PR that
+  # leaves Cargo.lock alone rebuilds only the workspace crates it changed.
+  nix-build:
+    name: Nix build (crate2nix)
+    runs-on: [self-hosted, nixos, microvm]
+    steps:
+      - uses: actions/checkout@v7
+      # Plain bash, not the dev shell: this step needs nix and nothing else.
+      - name: nix build .#improvise
+        shell: bash
+        run: nix build --print-build-logs .#improvise
 
   wasm:
     name: wasm32 check (browser bundle crates)
@@ -410,7 +410,7 @@ jobs:
   # exists to stop.
   pages-deploy:
     name: Deploy to GitHub Pages
-    needs: [test, wasm, js, browser, harness-lint, kb, build]
+    needs: [test, wasm, js, browser, harness-lint, kb, build, nix-build]
     if: github.event_name == 'push' && github.ref == 'refs/heads/main'
     runs-on: [self-hosted, nixos, microvm]
     permissions: