fix: npm publish --tag alpha when building an alpha release (#4112)

This updates our release process so that when we build an alpha of the
Codex CLI (as determined by pushing a tag of the format
`rust-v<cli-version>-alpha.<alpha-version>`), we will now publish the
corresponding npm module publicly, but under the `alpha` tag. As you can
see, this PR adds `--tag alpha` to the `npm publish` command, as
appropriate.

.github/workflows/rust-release.yml

@@ -173,6 +173,8 @@ jobs:
     outputs:
       version: ${{ steps.release_name.outputs.name }}
       tag: ${{ github.ref_name }}
+      should_publish_npm: ${{ steps.npm_publish_settings.outputs.should_publish }}
+      npm_tag: ${{ steps.npm_publish_settings.outputs.npm_tag }}
 
     steps:
       - name: Checkout repository
@@ -193,6 +195,25 @@ jobs:
           version="${GITHUB_REF_NAME#rust-v}"
           echo "name=${version}" >> $GITHUB_OUTPUT
 
+      - name: Determine npm publish settings
+        id: npm_publish_settings
+        env:
+          VERSION: ${{ steps.release_name.outputs.name }}
+        run: |
+          set -euo pipefail
+          version="${VERSION}"
+
+          if [[ "${version}" =~ ^[0-9]+\.[0-9]+\.[0-9]+$ ]]; then
+            echo "should_publish=true" >> "$GITHUB_OUTPUT"
+            echo "npm_tag=" >> "$GITHUB_OUTPUT"
+          elif [[ "${version}" =~ ^[0-9]+\.[0-9]+\.[0-9]+-alpha\.[0-9]+$ ]]; then
+            echo "should_publish=true" >> "$GITHUB_OUTPUT"
+            echo "npm_tag=alpha" >> "$GITHUB_OUTPUT"
+          else
+            echo "should_publish=false" >> "$GITHUB_OUTPUT"
+            echo "npm_tag=" >> "$GITHUB_OUTPUT"
+          fi
+
       # build_npm_package.py requires DotSlash when staging releases.
       - uses: facebook/install-dotslash@v2
       - name: Stage npm package
@@ -227,8 +248,8 @@ jobs:
   # July 31, 2025: https://github.blog/changelog/2025-07-31-npm-trusted-publishing-with-oidc-is-generally-available/
   # npm docs: https://docs.npmjs.com/trusted-publishers
   publish-npm:
-    # Skip this step for pre-releases (alpha/beta).
-    if: ${{ !contains(needs.release.outputs.version, '-') }}
+    # Publish to npm for stable releases and alpha pre-releases with numeric suffixes.
+    if: ${{ needs.release.outputs.should_publish_npm == 'true' }}
     name: publish-npm
     needs: release
     runs-on: ubuntu-latest
@@ -263,7 +284,17 @@ jobs:
 
       # No NODE_AUTH_TOKEN needed because we use OIDC.
       - name: Publish to npm
-        run: npm publish "${GITHUB_WORKSPACE}/dist/npm/codex-npm-${{ needs.release.outputs.version }}.tgz"
+        env:
+          VERSION: ${{ needs.release.outputs.version }}
+          NPM_TAG: ${{ needs.release.outputs.npm_tag }}
+        run: |
+          set -euo pipefail
+          tag_args=()
+          if [[ -n "${NPM_TAG}" ]]; then
+            tag_args+=(--tag "${NPM_TAG}")
+          fi
+
+          npm publish "${GITHUB_WORKSPACE}/dist/npm/codex-npm-${VERSION}.tgz" "${tag_args[@]}"
 
   update-branch:
     name: Update latest-alpha-cli branch