Make the PR workflow a real gate

- continue-on-error is removed; lint, test and build each have to pass,
  and fail-fast is off so each reports on its own
- after each step the tree must be unchanged (eslint --fix,
  packageInfo.ts written by the build)
- after build, scripts/check-built-manifests.py checks the package.json
  npm receives from each build/ directory
- push-main installs with --immutable and checks the manifests too
- the auto-approve and auto-merge bots are removed

.github/workflows/pr-any.yml

@@ -3,8 +3,9 @@ on: [pull_request]
 
 jobs:
   pr:
-    continue-on-error: true
     strategy:
+      # Each step reports on its own; one red step must not cancel the others.
+      fail-fast: false
       matrix:
         step: ['lint', 'test', 'build']
     runs-on: ubuntu-latest
@@ -17,5 +18,16 @@ jobs:
         node-version: 'lts/*'
     - name: ${{ matrix.step }}
       run: |
+        corepack enable
         yarn install --immutable
         yarn ${{ matrix.step }}
+    # `yarn lint` runs eslint --fix and `yarn build` rewrites packageInfo.ts,
+    # so both pass on a tree they changed. The committed tree must already be
+    # what they produce.
+    - name: tree unchanged
+      run: git diff --exit-code --stat
+    # The package.json each build/ directory holds is what npm receives: entry
+    # points must exist, no ./build/ or ./cjs/cjs/ paths, no workspace: ranges.
+    - name: check built manifests
+      if: matrix.step == 'build'
+      run: python3 scripts/check-built-manifests.py .