diff --git a/.github/workflows/platform-validation.yml b/.github/workflows/platform-validation.yml
new file mode 100644
index 0000000..b4aa39b
--- /dev/null
+++ b/.github/workflows/platform-validation.yml
@@ -0,0 +1,52 @@
+name: Platform Validation
+
+on:
+  push:
+    branches:
+      - main
+  pull_request:
+
+permissions:
+  contents: read
+
+jobs:
+  validate:
+    name: ${{ matrix.os }} / Python ${{ matrix.python-version }}
+    runs-on: ${{ matrix.os }}
+    strategy:
+      fail-fast: false
+      matrix:
+        os:
+          - ubuntu-latest
+          - macos-latest
+        python-version:
+          - "3.10"
+          - "3.11"
+          - "3.12"
+          - "3.13"
+
+    steps:
+      - name: Check out repository
+        uses: actions/checkout@v4
+
+      - name: Set up Python
+        uses: actions/setup-python@v5
+        with:
+          python-version: ${{ matrix.python-version }}
+
+      - name: Install development dependencies
+        run: python -m pip install -e ".[dev]"
+
+      - name: Run unit tests
+        run: python -m unittest discover -s tests
+
+      - name: Run capability diagnostics
+        run: python scripts/diagnose.py
+
+      - name: Run process smoke tests
+        run: |
+          python examples/process_smoke.py
+          python examples/async_process_smoke.py
+
+      - name: Build distribution artifacts
+        run: python -m build
diff --git a/README.md b/README.md
index 4b4ce93..bedc990 100644
--- a/README.md
+++ b/README.md
@@ -338,6 +338,27 @@ python examples/async_process_smoke.py
 
 They exercise hosted PowerShell, synchronous process-backed sessions, and async process-backed sessions.
 
+## Platform Validation Matrix
+
+LiveShell's automated platform coverage focuses on the base package behavior that should work on both macOS and Linux without optional extras:
+
+| Platform | Python | Automated checks |
+| --- | --- | --- |
+| Linux | 3.10, 3.11, 3.12, 3.13 | `python -m unittest discover -s tests`, `python scripts/diagnose.py`, `python examples/process_smoke.py`, `python examples/async_process_smoke.py`, `python -m build` |
+| macOS | 3.10, 3.11, 3.12, 3.13 | `python -m unittest discover -s tests`, `python scripts/diagnose.py`, `python examples/process_smoke.py`, `python examples/async_process_smoke.py`, `python -m build` |
+
+This matrix is enforced in GitHub Actions by the `Platform Validation` workflow in `.github/workflows/platform-validation.yml`.
+
+Hosted PowerShell remains an optional path because it requires both a local PowerShell installation and the `powershell` extra:
+
+```powershell
+python -m pip install ".[powershell]"
+python scripts/diagnose.py --preload
+python examples/powershell_smoke.py
+```
+
+Run those hosted PowerShell checks manually on the target macOS/Linux machine when that optional integration matters for a release or deployment.
+
 ## Behavior And Limitations
 
 Process-backed sessions such as `Cmd` and `Bash` keep one child process alive and send commands through it. They preserve shell state, but they are not full terminal or PTY emulators.
diff --git a/scripts/diagnose.py b/scripts/diagnose.py
index fc3d055..34108b3 100644
--- a/scripts/diagnose.py
+++ b/scripts/diagnose.py
@@ -31,7 +31,7 @@ def main() -> int:
     pythonnet_found = importlib.util.find_spec("pythonnet") is not None
     print(f"pythonnet installed: {pythonnet_found}")
     if not pythonnet_found:
-        print("Install with: python -m pip install -r requirements.txt")
+        print('Optional for hosted PowerShell: python -m pip install ".[powershell]"')
 
     installation = PowerShell.find_installation()
     print(f"PowerShell available: {installation is not None}")