fix(testing/ci/tooling): consistent unittest, venv guidance, runnable lab commands

- #9: standardize the test chain on stdlib unittest (nothing-to-install, which
  keeps M13's claims true and its planted bug intact). Aligned M5/M14/M16 prose,
  M14 lab/test_tasks.py, and ci/gitlab starters; ruff stays the only pip install.
- #20: add venv / PEP 668 / which-python guidance to M20 (+ M14/M15 local
  installs); point MCP config at the venv's absolute python.
- #21: replace M21 Part D's empty `git diff HEAD~1` with `git log -p` (no
  .gitignore added — device preserved).
- #22: add a dependency-install step before M23's green baseline on a fresh clone.
- #23: M24 reviewer/triage now tolerate code-fence-wrapped JSON (stdlib only);
  feature.patch trap untouched.
- #28: fix M27 Part D CI snippet path (working-directory) and require the gate to
  target a varying candidate; swapped_model regression kept as the fixture.

Closes #9
Closes #20
Closes #21
Closes #22
Closes #23
Closes #28

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01TfzV5QvtPDz8LJS3Pu5VLT

modules/14-continuous-integration/lab/ci-starter.yml

@@ -33,14 +33,16 @@ jobs:
         with:
           python-version: "3.12"
 
-      # Step 3: install the tools the checks need — the test runner and the linter from Module 13.
+      # Step 3: install the linter (ruff), the new tool this module adds. The test runner is
+      # Python's standard-library unittest from Module 13 — nothing to install for it.
       - name: Install tools
-        run: pip install pytest ruff
+        run: pip install ruff
 
       # Step 4: lint. Style and obvious-mistake check. Fails the job on any finding (non-zero exit).
       - name: Lint
         run: ruff check .
 
-      # Step 5: test. The Module 13 tests. A single failing assertion fails the whole job.
+      # Step 5: test. The Module 13 tests, run with the stdlib unittest runner. A single failing
+      # assertion fails the whole job.
       - name: Test
-        run: pytest -q
+        run: python -m unittest

modules/14-continuous-integration/lab/gitlab-ci-starter.yml

@@ -17,6 +17,6 @@ check:
   # of "runs-on: ubuntu-latest" plus "set up Python".
   image: python:3.12
   script:
-    - pip install pytest ruff
-    - ruff check .      # lint
-    - pytest -q         # test
+    - pip install ruff
+    - ruff check .          # lint
+    - python -m unittest    # test (stdlib runner from Module 13 — nothing to install)

modules/14-continuous-integration/lab/test_tasks.py

@@ -1,36 +1,41 @@
 """Tests for the tasks-app core logic — the kind of suite Module 13 has you write.
 
 Reproduced here so this module's lab is self-contained: if you already wrote tests in Module 13,
-use those instead. Run locally with `pytest -q` from the project folder. CI runs exactly this.
+use those instead. Standard-library `unittest`, exactly like Module 13 — nothing to install.
+Run locally with `python -m unittest` from the project folder. CI runs exactly this.
 """
 
+import unittest
+
 from tasks import TaskList
 
 
-def test_add_appends_a_task():
-    tl = TaskList()
-    tl.add("write the CI lesson")
-    assert len(tl.tasks) == 1
-    assert tl.tasks[0].title == "write the CI lesson"
-    assert tl.tasks[0].done is False
+class TestTaskList(unittest.TestCase):
+    def test_add_appends_a_task(self):
+        tl = TaskList()
+        tl.add("write the CI lesson")
+        self.assertEqual(len(tl.tasks), 1)
+        self.assertEqual(tl.tasks[0].title, "write the CI lesson")
+        self.assertFalse(tl.tasks[0].done)
+
+    def test_complete_marks_a_task_done(self):
+        tl = TaskList()
+        tl.add("ship it")
+        tl.complete(0)
+        self.assertTrue(tl.tasks[0].done)
+
+    def test_pending_excludes_completed_tasks(self):
+        tl = TaskList()
+        tl.add("a")
+        tl.add("b")
+        tl.complete(0)
+        pending = tl.pending()
+        self.assertEqual(len(pending), 1)
+        self.assertEqual(pending[0].title, "b")
+
+    def test_render_is_friendly_when_empty(self):
+        self.assertEqual(TaskList().render(), "(no tasks yet)")
 
 
-def test_complete_marks_a_task_done():
-    tl = TaskList()
-    tl.add("ship it")
-    tl.complete(0)
-    assert tl.tasks[0].done is True
-
-
-def test_pending_excludes_completed_tasks():
-    tl = TaskList()
-    tl.add("a")
-    tl.add("b")
-    tl.complete(0)
-    pending = tl.pending()
-    assert len(pending) == 1
-    assert pending[0].title == "b"
-
-
-def test_render_is_friendly_when_empty():
-    assert TaskList().render() == "(no tasks yet)"
+if __name__ == "__main__":
+    unittest.main()