diff --git a/.gitea/workflows/.trigger b/.gitea/workflows/.trigger
deleted file mode 100644
index 997b246..0000000
--- a/.gitea/workflows/.trigger
+++ /dev/null
@@ -1 +0,0 @@
-ci: re-run after routing fix
diff --git a/.gitea/workflows/check.yml b/.gitea/workflows/check.yml
index 186278f..55545f4 100644
--- a/.gitea/workflows/check.yml
+++ b/.gitea/workflows/check.yml
@@ -16,6 +16,18 @@ on:
 jobs:
   gate:
     runs-on: veron-1
+    # Run IN a Python 3.12 image rather than trusting the runner image's
+    # toolchain. The first real CI run wedged here: catthehacker/ubuntu:act-22.04
+    # ships Python 3.10.12, this project declares requires-python >=3.12, and pip
+    # answered that by backtracking through the entire release history of every
+    # dependency looking for something 3.10-compatible. It churned for 14 minutes
+    # at 100% CPU with `-q` hiding all of it, and would have churned until the
+    # runner timeout. A version mismatch presenting as a hang, not an error.
+    container:
+      image: python:3.12-bookworm
+    # And a hard ceiling, so a wedged step is a red check in minutes rather than
+    # an occupied runner for half an hour.
+    timeout-minutes: 12
     services:
       postgres:
         image: postgres:16-alpine
@@ -32,8 +44,10 @@ jobs:
 
       - name: install
         run: |
+          python3 --version
           python3 -m venv .venv
-          .venv/bin/pip install -q -e ".[dev]"
+          .venv/bin/pip install -q --upgrade pip
+          .venv/bin/pip install -e ".[dev]"
 
       - name: lint
         run: .venv/bin/ruff check api scripts
diff --git a/api/tests/test_invariants.py b/api/tests/test_invariants.py
index 2aee0e9..395e18f 100644
--- a/api/tests/test_invariants.py
+++ b/api/tests/test_invariants.py
@@ -461,3 +461,33 @@ def test_g75_workflows_use_a_label_this_runner_actually_provides():
                 continue
             label = ln.split("runs-on:")[1].strip()
             assert label in provided, f"{wf.name}: '{label}' is not a provided label"
+
+
+def test_g73_workflow_pins_a_python_that_satisfies_requires_python():
+    """The first real CI run wedged for 14 minutes because the runner image
+    ships Python 3.10 and this project requires 3.12: pip answered by
+    backtracking through every historical version of every dependency, at full
+    CPU, silently. A version mismatch presenting as a hang rather than an
+    error."""
+    import re as _re
+
+    pyproject = (ROOT / "pyproject.toml").read_text()
+    m = _re.search(r'requires-python\s*=\s*">=(\d+)\.(\d+)"', pyproject)
+    assert m, "pyproject declares no requires-python"
+    major, minor = int(m.group(1)), int(m.group(2))
+
+    for wf in ROOT.rglob(".gitea/workflows/*.y*ml"):
+        text = wf.read_text()
+        img = _re.search(r"image:\s*python:(\d+)\.(\d+)", text)
+        assert img, f"{wf.name}: job does not pin a python image"
+        assert (int(img.group(1)), int(img.group(2))) >= (major, minor), (
+            f"{wf.name}: pins python {img.group(0)} but the project requires "
+            f">={major}.{minor}"
+        )
+
+
+def test_g73_every_job_has_a_timeout():
+    """A wedged step should be a red check in minutes, not an occupied runner
+    for half an hour."""
+    for wf in ROOT.rglob(".gitea/workflows/*.y*ml"):
+        assert "timeout-minutes:" in wf.read_text(), f"{wf.name}: no job timeout"