add python-semantic-release github action

sets up build deps, lints, prevents releases from racing, automatically
updates release variables, publishes releases to github and tags them.

TODO: pypi distribution

Author: the-roaring

.github/workflows/release.yml

@@ -0,0 +1,157 @@
+name: Semantic Release
+
+on:
+  push:
+    branches:
+      - main
+  workflow_dispatch:
+
+permissions:
+  contents: write
+  pull-requests: write
+  id-token: write
+
+jobs:
+  release:
+    runs-on: ubuntu-latest
+    concurrency:
+      group: ${{ github.workflow }}-release-${{ github.ref_name }}
+      cancel-in-progress: false
+
+    permissions:
+      contents: write
+
+    steps:
+      # Note: We checkout the repository at the branch that triggered the workflow
+      # with the entire history to ensure to match PSR's release branch detection
+      # and history evaluation.
+      # However, we forcefully reset the branch to the workflow sha because it is
+      # possible that the branch was updated while the workflow was running. This
+      # prevents accidentally releasing un-evaluated changes.
+      - name: Setup | Checkout Repository on Release Branch
+        uses: actions/checkout@v4
+        with:
+          ref: ${{ github.ref_name }}
+          fetch-depth: 0
+
+      - name: Setup | Force release branch to be at workflow sha
+        run: |
+          git reset --hard ${{ github.sha }}
+
+      - name: Set up Python
+        uses: actions/setup-python@v4
+        with:
+          python-version: "3.11"
+
+      - name: Install dependencies
+        run: |
+          python -m pip install --upgrade pip
+          pip install build twine wheel setuptools ruff black
+          pip install -r requirements.txt
+          if [ -f requirements-dev.txt ]; then pip install -r requirements-dev.txt; fi
+        # TODO add playwright install for CI pytest
+        # TODO update to use uv or move into build_command in pyproject.toml
+
+      - name: Run linting and formatting
+        run: |
+          # Run linter
+          black --check --diff stagehand
+
+          # Run Ruff formatter check (without modifying files)
+          ruff check stagehand
+
+      # TODO: add back as soon as CI is passing
+      # - name: Run tests
+      #   run: |
+      #     pytest
+
+      - name: Evaluate | Verify upstream has NOT changed
+        # Last chance to abort before causing an error as another PR/push was applied to
+        # the upstream branch while this workflow was running. This is important
+        # because we are committing a version change (--commit). You may omit this step
+        # if you have 'commit: false' in your configuration.
+        #
+        # You may consider moving this to a repo script and call it from this step instead
+        # of writing it in-line.
+        shell: bash
+        run: |
+          set +o pipefail
+
+          UPSTREAM_BRANCH_NAME="$(git status -sb | head -n 1 | cut -d' ' -f2 | grep -E '\.{3}' | cut -d'.' -f4)"
+          printf '%s\n' "Upstream branch name: $UPSTREAM_BRANCH_NAME"
+
+          set -o pipefail
+
+          if [ -z "$UPSTREAM_BRANCH_NAME" ]; then
+              printf >&2 '%s\n' "::error::Unable to determine upstream branch name!"
+              exit 1
+          fi
+
+          git fetch "${UPSTREAM_BRANCH_NAME%%/*}"
+
+          if ! UPSTREAM_SHA="$(git rev-parse "$UPSTREAM_BRANCH_NAME")"; then
+              printf >&2 '%s\n' "::error::Unable to determine upstream branch sha!"
+              exit 1
+          fi
+
+          HEAD_SHA="$(git rev-parse HEAD)"
+
+          if [ "$HEAD_SHA" != "$UPSTREAM_SHA" ]; then
+              printf >&2 '%s\n' "[HEAD SHA] $HEAD_SHA != $UPSTREAM_SHA [UPSTREAM SHA]"
+              printf >&2 '%s\n' "::error::Upstream has changed, aborting release..."
+              exit 1
+          fi
+
+          printf '%s\n' "Verified upstream branch has not changed, continuing with release..."
+
+      - name: Action | Semantic Version Release
+        id: release
+        uses: python-semantic-release/[email protected]
+        with:
+          github_token: ${{ secrets.GITHUB_TOKEN }}
+          git_committer_name: "github-actions"
+          git_committer_email: "[email protected]"
+
+      - name: Publish | Upload to GitHub Release Assets
+        uses: python-semantic-release/[email protected]
+        if: steps.release.outputs.released == 'true'
+        with:
+          github_token: ${{ secrets.GITHUB_TOKEN }}
+          tag: ${{ steps.release.outputs.tag }}
+
+      - name: Upload | Distribution Artifacts
+        uses: actions/upload-artifact@v4
+        with:
+          name: distribution-artifacts
+          path: dist
+          if-no-files-found: error
+
+  deploy:
+    # 1. Separate out the deploy step from the publish step to run each step at
+    #    the least amount of token privilege
+    # 2. Also, deployments can fail, and its better to have a separate job if you need to retry
+    #    and it won't require reversing the release.
+    runs-on: ubuntu-latest
+    needs: release
+    if: ${{ needs.release.outputs.released == 'true' }}
+
+    permissions:
+      contents: read
+      id-token: write
+
+    steps:
+      - name: Setup | Download Build Artifacts
+        uses: actions/download-artifact@v4
+        id: artifact-download
+        with:
+          name: distribution-artifacts
+          path: dist
+
+      # TODO set up trusted publisher
+      # see https://docs.pypi.org/trusted-publishers/
+      - name: Publish package distributions to PyPI
+        uses: pypa/gh-action-pypi-publish@release/v1
+        with:
+          packages-dir: dist
+          print-hash: true
+          verbose: true