diff --git a/.github/actions/bootstrap-poetry/action.yaml b/.github/actions/bootstrap-poetry/action.yaml
index cec135d89..1ab66f8c0 100644
--- a/.github/actions/bootstrap-poetry/action.yaml
+++ b/.github/actions/bootstrap-poetry/action.yaml
@@ -35,10 +35,7 @@ runs:
         allow-prereleases: ${{ inputs.python-prereleases == 'true' }}
         update-environment: false
 
-    - run: >
-        pipx install \
-          ${{ inputs.python-version != 'default' && format('--python "{0}"', steps.setup-python.outputs.python-path) || '' }} \
-          '${{ inputs.poetry-spec }}'
+    - run: pipx install ${{ inputs.python-version != 'default' && format('--python "{0}"', steps.setup-python.outputs.python-path) || '' }} '${{ inputs.poetry-spec }}'
       shell: bash
 
     # Enable handling long path names (+260 char) on the Windows platform
diff --git a/.github/actions/poetry-install/action.yaml b/.github/actions/poetry-install/action.yaml
index 9436303e3..37109a0de 100644
--- a/.github/actions/poetry-install/action.yaml
+++ b/.github/actions/poetry-install/action.yaml
@@ -16,10 +16,6 @@ outputs:
     description: Whether an exact cache hit occured
     value: ${{ steps.cache.outputs.cache-hit }}
 
-defaults:
-  run:
-    working-directory: ${{ inputs.path }}
-
 runs:
   using: composite
   steps:
@@ -48,10 +44,13 @@ runs:
         enableCrossOsArchive: true
 
     - run: poetry install ${{ inputs.args }}
+      working-directory: ${{ inputs.path }}
       shell: bash
 
     - run: poetry env info
+      working-directory: ${{ inputs.path }}
       shell: bash
 
     - run: poetry show
+      working-directory: ${{ inputs.path }}
       shell: bash
diff --git a/.github/workflows/.tests-matrix.yaml b/.github/workflows/.tests-matrix.yaml
new file mode 100644
index 000000000..68fa9071d
--- /dev/null
+++ b/.github/workflows/.tests-matrix.yaml
@@ -0,0 +1,98 @@
+# Reusable workflow consumed by tests.yaml; used to share a single matrix across jobs.
+on:
+  workflow_call:
+    inputs:
+      runner:
+        required: true
+        type: string
+      python-version:
+        required: true
+        type: string
+      run-mypy:
+        required: true
+        type: boolean
+      run-pytest:
+        required: true
+        type: boolean
+      run-pytest-poetry:
+        required: true
+        type: boolean
+
+defaults:
+  run:
+    shell: bash
+
+jobs:
+  mypy:
+    name: mypy
+    runs-on: ${{ inputs.runner }}
+    if: inputs.run-mypy
+    steps:
+      - uses: actions/checkout@b4ffde65f46336ab88eb53be808477a3936bae11 # v4
+
+      - uses: ./.github/actions/bootstrap-poetry
+        id: bootstrap-poetry
+        with:
+          python-version: ${{ inputs.python-version }}
+
+      - uses: ./.github/actions/poetry-install
+
+      - uses: actions/cache@0c45773b623bea8c8e75f6c82b208c3cf94ea4f9 # v4
+        with:
+          path: .mypy_cache
+          key: mypy-${{ runner.os }}-py${{ steps.bootstrap-poetry.outputs.python-version }}-${{ hashFiles('pyproject.toml', 'poetry.lock') }}
+          restore-keys: |
+            mypy-${{ runner.os }}-py${{ steps.bootstrap-poetry.outputs.python-version }}-
+            mypy-${{ runner.os }}-
+
+      - run: poetry run mypy
+
+  pytest:
+    name: pytest
+    runs-on: ${{ inputs.runner }}
+    if: inputs.run-pytest
+    steps:
+      - uses: actions/checkout@b4ffde65f46336ab88eb53be808477a3936bae11 # v4
+
+      - uses: ./.github/actions/bootstrap-poetry
+        with:
+          python-version: ${{ inputs.python-version }}
+
+      - uses: ./.github/actions/poetry-install
+        with:
+          args: --with github-actions
+
+      - run: poetry run pytest --integration -v
+
+      - run: git diff --exit-code --stat HEAD
+
+  pytest-poetry:
+    name: pytest (Poetry)
+    runs-on: ${{ inputs.runner }}
+    if: inputs.run-pytest-poetry
+    steps:
+      - uses: actions/checkout@b4ffde65f46336ab88eb53be808477a3936bae11 # v4
+        with:
+          path: poetry-core
+
+      - uses: actions/checkout@b4ffde65f46336ab88eb53be808477a3936bae11 # v4
+        with:
+          path: poetry
+          repository: python-poetry/poetry
+
+      - uses: ./poetry-core/.github/actions/bootstrap-poetry
+        with:
+          python-version: ${{ inputs.python-version }}
+
+      - uses: ./poetry-core/.github/actions/poetry-install
+        with:
+          args: --with github-actions
+          path: ./poetry
+
+      - run: poetry add ../poetry-core
+        working-directory: ./poetry
+
+      - run: poetry run pytest -v
+        working-directory: ./poetry
+
+      - run: git -C poetry diff --exit-code --stat HEAD
diff --git a/.github/workflows/downstream.yaml b/.github/workflows/downstream.yaml
deleted file mode 100644
index 9e53293c8..000000000
--- a/.github/workflows/downstream.yaml
+++ /dev/null
@@ -1,76 +0,0 @@
-name: Poetry Downstream Tests
-
-on:
-  pull_request: {}
-  push:
-    branches: [main]
-
-jobs:
-  tests:
-    name: ${{ matrix.ref }}
-    runs-on: ubuntu-latest
-    strategy:
-      matrix:
-        ref: ["main"]
-      fail-fast: false
-    defaults:
-      run:
-        shell: bash
-    steps:
-      - uses: actions/checkout@v4
-        with:
-          path: poetry-core
-
-      - uses: actions/checkout@v4
-        with:
-          path: poetry
-          repository: python-poetry/poetry
-          ref: ${{ matrix.ref }}
-
-      - name: Set up Python 3.10
-        uses: actions/setup-python@v5
-        with:
-          python-version: "3.10"
-
-      - name: Get full python version
-        id: full-python-version
-        run: echo version=$(python -c "import sys; print('-'.join(str(v) for v in sys.version_info))") >> $GITHUB_OUTPUT
-
-      - name: Set up Poetry
-        run: |
-          pip install poetry
-          poetry config virtualenvs.in-project true
-
-      - name: Set up cache
-        uses: actions/cache@v4
-        id: cache
-        with:
-          path: ./poetry/.venv
-          key: venv-${{ steps.full-python-version.outputs.version }}-${{ hashFiles('**/poetry.lock') }}
-
-      - name: Ensure cache is healthy
-        if: steps.cache.outputs.cache-hit == 'true'
-        working-directory: ./poetry
-        run: timeout 10s poetry run pip --version >/dev/null 2>&1 || rm -rf .venv
-
-      - name: Switch downstream to development poetry-core
-        working-directory: ./poetry
-        run: |
-          # remove poetry-core from main group to avoid version conflicts
-          # with a potential entry in the test group
-          poetry remove poetry-core
-          # add to test group to overwrite a potential entry in that group
-          poetry add --lock --group test ../poetry-core
-
-      - name: Install downstream dependencies
-        working-directory: ./poetry
-        run: |
-          # force update of directory dependency in cached venv
-          # (even if directory dependency with same version is already installed)
-          poetry run pip uninstall -y poetry-core
-          poetry install
-
-      # TODO: mark run as success even when this fails and add comment to PR instead
-      - name: Run downstream test suite
-        working-directory: ./poetry
-        run: poetry run pytest
diff --git a/.github/workflows/tests.yaml b/.github/workflows/tests.yaml
index 42a7b9a56..848439558 100644
--- a/.github/workflows/tests.yaml
+++ b/.github/workflows/tests.yaml
@@ -1,81 +1,102 @@
 name: Tests
 
 on:
-  pull_request: {}
+  merge_group:
+  pull_request:
   push:
-    branches: [main]
+
+concurrency:
+  group: ${{ github.workflow }}-${{ github.ref }}
+  cancel-in-progress: ${{ github.event_name == 'pull_request' }}
+
+defaults:
+  run:
+    shell: bash
 
 env:
   PYTHONWARNDEFAULTENCODING: 'true'
 
 jobs:
-  tests:
-    name: ${{ matrix.os }} / ${{ matrix.python-version }}
-    runs-on: "${{ matrix.os }}-latest"
+  changes:
+    name: Detect changed files
+    runs-on: ubuntu-latest
+    outputs:
+      project: ${{ steps.changes.outputs.project }}
+      src: ${{ steps.changes.outputs.src }}
+      tests: ${{ steps.changes.outputs.tests }}
+    steps:
+      - uses: actions/checkout@b4ffde65f46336ab88eb53be808477a3936bae11 # v4
+
+      - uses: dorny/paths-filter@de90cc6fb38fc0963ad72b210f1f284cd68cea36 # v3
+        id: changes
+        with:
+          filters: |
+            workflow: &workflow
+              - '.github/actions/**'
+              - '.github/workflows/tests.yaml'
+              - '.github/workflows/.tests-matrix.yaml'
+            project: &project
+              - *workflow
+              - 'poetry.lock'
+              - 'pyproject.toml'
+            src:
+              - *project
+              - 'src/**/*.py'
+            tests:
+              - *project
+              - 'src/**/*.py'
+              - 'tests/**'
+
+  lockfile:
+    name: Check poetry.lock
+    runs-on: ubuntu-latest
+    if: needs.changes.outputs.project == 'true'
+    needs: changes
+    steps:
+      - uses: actions/checkout@b4ffde65f46336ab88eb53be808477a3936bae11 # v4
+
+      - uses: ./.github/actions/bootstrap-poetry
+
+      - run: poetry check --lock
+
+  tests-matrix:
+    # Use this matrix with multiple jobs defined in a reusable workflow:
+    uses: ./.github/workflows/.tests-matrix.yaml
+    name: ${{ matrix.os.name }} (Python ${{ matrix.python-version }})
+    if: '!failure() && !cancelled()'
+    needs:
+      - lockfile
+      - changes
+    with:
+      runner: ${{ matrix.os.image }}
+      python-version: ${{ matrix.python-version }}
+      run-mypy: ${{ needs.changes.outputs.src == 'true' }}
+      run-pytest: ${{ needs.changes.outputs.tests == 'true' }}
+      run-pytest-poetry: ${{ needs.changes.outputs.src == 'true' }}
+    secrets: inherit
     strategy:
       matrix:
-        os: [Ubuntu, MacOS, Windows]
+        os:
+          - name: Ubuntu
+            image: ubuntu-22.04
+          - name: macOS
+            image: macos-13
+          - name: Windows
+            image: windows-2022
         python-version: ["3.8", "3.9", "3.10", "3.11", "3.12"]
         include:
-          - os: Ubuntu
-            python-version: pypy-3.8
+          - os: {name: Ubuntu, image: ubuntu-22.04}
+            python-version: pypy3.9
+          - os: {name: Ubuntu, image: ubuntu-22.04}
+            python-version: pypy3.10
       fail-fast: false
-    defaults:
-      run:
-        shell: bash
-    steps:
-      - uses: actions/checkout@v4
-
-      - name: Set up Python ${{ matrix.python-version }}
-        uses: actions/setup-python@v5
-        with:
-          python-version: ${{ matrix.python-version }}
-
-      - name: Get full Python version
-        id: full-python-version
-        run: echo version=$(python -c "import sys; print('-'.join(str(v) for v in sys.version_info))") >> $GITHUB_OUTPUT
-
-      - name: Bootstrap poetry
-        run: |
-          curl -sSL https://install.python-poetry.org | python - -y
 
-      - name: Update PATH
-        if: ${{ matrix.os != 'Windows' }}
-        run: echo "$HOME/.local/bin" >> $GITHUB_PATH
-
-      - name: Update Path for Windows
-        if: ${{ matrix.os == 'Windows' }}
-        run: echo "$APPDATA\Python\Scripts" >> $GITHUB_PATH
-
-      - name: Configure poetry
-        run: poetry config virtualenvs.in-project true
-
-      - name: Set up cache
-        uses: actions/cache@v4
-        id: cache
-        with:
-          path: .venv
-          key: venv-${{ runner.os }}-${{ steps.full-python-version.outputs.version }}-${{ hashFiles('**/poetry.lock') }}
-
-      - name: Ensure cache is healthy
-        if: steps.cache.outputs.cache-hit == 'true'
-        run: |
-          # `timeout` is not available on macOS, so we define a custom function.
-          [ "$(command -v timeout)" ] || function timeout() { perl -e 'alarm shift; exec @ARGV' "$@"; }
-          # Using `timeout` is a safeguard against the Poetry command hanging for some reason.
-          timeout 10s poetry run pip --version || rm -rf .venv
-
-      - name: Check lock file
-        run: poetry lock --check
-
-      - name: Install dependencies
-        run: poetry install
-
-      - name: Run tests
-        run: poetry run python -m pytest -p no:sugar -q tests/
-
-      - name: Run integration tests
-        run: poetry run python -m pytest -p no:sugar --integration -q tests/integration
-
-      - name: Run mypy
-        run: poetry run mypy
+  status:
+    name: Status
+    runs-on: ubuntu-latest
+    if: '!cancelled()'
+    needs:
+      - lockfile
+      - tests-matrix
+    steps:
+      - run: ${{ (contains(needs.*.result, 'failure') || contains(needs.*.result, 'cancelled')) && 'false' || 'true' }}