fix(ci): smoke guard catches tagless builds; DEBUG import must hit the install; pin more workflow invariants

Review findings on PR #13:
- release-branch-semver gives 0.1.0.devN without tags, so the 0.0 guard
  never fired; check_version() now requires >= 0.2 (unit-tested)
- the APPSKELLINGTON_DEBUG child import could resolve the source tree from
  the cwd and false-pass; it now reports its location and must match
- test_ci_workflow: no continue-on-error, matrix python drives container
  and UV_PYTHON, WIP gate compared whole (mutation-tested)

Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>

tests/test_ci_workflow.py

@@ -60,10 +60,27 @@ def test_superseded_pr_runs_cancel_but_push_runs_never_do():
 
 
 def test_every_job_is_wip_gated():
+    # Compared whole, not by substring: `&&` turned into `||` must fail.
+    gate = "github.event_name != 'pull_request' || ( %s && %s )" % WIP_CLAUSES
     for name, job in load()["jobs"].items():
         cond = flat(job.get("if", ""))
-        for clause in WIP_CLAUSES:
-            assert clause in cond, "%s lacks WIP gate clause %s" % (name, clause)
+        assert cond in (gate, "always() && ( %s )" % gate), name
+
+
+def test_no_gate_can_be_softened_by_continue_on_error():
+    # continue-on-error makes needs.<job>.result read success, so ci-ok
+    # would go green over a failure.
+    for name, job in load()["jobs"].items():
+        assert "continue-on-error" not in job, name
+        for step in job.get("steps", []):
+            assert "continue-on-error" not in step, name
+
+
+def test_each_lane_really_runs_its_matrix_python():
+    test = load()["jobs"]["test"]
+    assert test["container"] == "python:${{ matrix.python }}"
+    assert test["env"]["UV_PYTHON"] == "${{ matrix.python }}"
+    assert test["env"]["UV_PYTHON_DOWNLOADS"] == "never"
 
 
 def test_matrix_matches_requires_python():

tests/test_smoke_import.py

@@ -0,0 +1,35 @@
+"""Unit tests for scripts/smoke_import.py's version checks."""
+
+import importlib.util
+import pathlib
+
+import pytest
+
+SCRIPT = pathlib.Path(__file__).resolve().parent.parent / "scripts" / "smoke_import.py"
+spec = importlib.util.spec_from_file_location("smoke_import", SCRIPT)
+smoke_import = importlib.util.module_from_spec(spec)
+spec.loader.exec_module(smoke_import)
+
+
+@pytest.mark.parametrize(
+    "version",
+    [
+        "0.0.0",
+        "0.0.1.dev3+gabc1234",
+        # release-branch-semver with no tags reachable (shallow clone):
+        "0.1.0.dev1+g6bd717f23",
+    ],
+)
+def test_tagless_versions_are_rejected(version):
+    with pytest.raises(SystemExit, match="no tags"):
+        smoke_import.check_version(version, expected=None)
+
+
+@pytest.mark.parametrize("version", ["0.2.3", "0.3.0.dev23+gc361b286c", "1.0.0"])
+def test_tag_derived_versions_pass(version):
+    smoke_import.check_version(version, expected=None)
+
+
+def test_expected_version_must_match_exactly():
+    with pytest.raises(SystemExit, match="expected version 0.2.3"):
+        smoke_import.check_version("0.2.3.dev1", expected="0.2.3")