Gate publication on source regression tests

Signed-off-by: Loren Eteval <loren.eteval@proton.me>

.github/AGENTS.md

@@ -41,9 +41,11 @@ exceptions; it does not define the source test suite or imply that every package
 - Validate YAML and every affected expression/shell. Trace each changed matrix row through dependency installation,
   source/native import checks, Nuitka/installer output, packaged architecture/dependency checks, artifact upload, and tag
   gates. When a target cannot run locally, add a narrow CI assertion that fails before publication with a useful reason.
-- The current workflow performs packaging/import/native checks but does not run the unittest behavioral suite. Do
-  not call an artifact build a regression-test pass; use `tests/README.md` for source verification. Check actual
-  `needs` and tag gates rather than assuming a downstream publish job runs on every build. Follow each publication
+- `workflows/source-tests.yml` runs isolated source unittest discovery on Windows, Linux, and macOS and is a
+  required dependency of PyPI publication through `deploy-pypi.yml`. It can also run manually. Daily binary
+  builds retain their separate artifact scope. Source tests do not establish packaged behavior or Python/Qt
+  floors beyond their matrix. Do not call an artifact build a regression-test pass; use `tests/README.md` for
+  source verification. Check actual `needs` and tag gates rather than assuming a downstream publish job runs on every build. Follow each publication
   dependency back to its required artifact checks; upload success alone does not establish release eligibility.
 - Revalidate version/architecture claims against the current matrix instead of duplicating all pins here. When build
   topology intentionally changes, update this scope and follow every consumer through upload and publication.

.github/workflows/deploy-pypi.yml

@@ -24,6 +24,10 @@ defaults:
     shell: bash
 
 jobs:
+  source-tests:
+    name: Source regression tests
+    uses: ./.github/workflows/source-tests.yml
+
   build-distribution:
     name: Build distribution
     runs-on: ubuntu-latest
@@ -60,6 +64,7 @@ jobs:
     name: Publish Python distribution to PyPI
     if: startsWith(github.ref, 'refs/tags/')  # only publish to PyPI on tag pushes
     needs:
+      - source-tests
       - build-distribution
       - deploy-binaries
     runs-on: ubuntu-latest

.github/workflows/source-tests.yml

@@ -0,0 +1,33 @@
+name: Source regression tests
+
+on:
+  workflow_call:
+  workflow_dispatch:
+
+permissions:
+  contents: read
+
+jobs:
+  unittest:
+    name: Source tests on ${{ matrix.os }}
+    runs-on: ${{ matrix.os }}
+    timeout-minutes: 30
+    strategy:
+      fail-fast: false
+      matrix:
+        os: [ubuntu-22.04, windows-2025, macos-14]
+    env:
+      QT_QPA_PLATFORM: offscreen
+      PYTHONUTF8: "1"
+    steps:
+      - uses: actions/checkout@v7
+      - uses: actions/setup-python@v7
+        with:
+          python-version: "3.13"
+      - name: Install Linux Qt runtime libraries
+        if: runner.os == 'Linux'
+        run: sudo apt-get update && sudo apt-get install -y libegl1 libopengl0
+      - name: Install source test dependencies
+        run: python -m pip install -r requirements.txt "PySide6-Essentials==6.8.3" "PySide6-Addons==6.8.3"
+      - name: Run isolated behavioral and resource tests
+        run: python -m unittest discover -s tests -v