Make Gate 0 fixtures deterministic on supported hosts

scripts/dev-env.sh

@@ -21,6 +21,7 @@ set -euo pipefail
 ROOT="$(cd "$(dirname "${BASH_SOURCE[0]}")/.." && pwd)"
 VENV="${CATHEDRAL_DEV_VENV:-$ROOT/.venv}"
 PYTEST_PIN="pytest==8.3.0"
+SETUPTOOLS_PIN="setuptools==80.9.0"
 
 find_supported_python() {
     if [ -n "${PYTHON:-}" ]; then echo "$PYTHON"; return; fi
@@ -45,7 +46,7 @@ if [ ! -x "$VENV/bin/python" ]; then
     "$BASE" -m venv "$VENV"
 fi
 "$VENV/bin/python" -m pip install --quiet --upgrade pip
-"$VENV/bin/python" -m pip install --quiet "$PYTEST_PIN"
+"$VENV/bin/python" -m pip install --quiet "$PYTEST_PIN" "$SETUPTOOLS_PIN"
 
 echo "provisioned $VENV"
 echo "  python: $("$VENV/bin/python" -V 2>&1)"

tests/_bundle_fixture.py

@@ -249,7 +249,14 @@ def _wheel(self, name: str, module: str, scripts: dict[str, str], extra_dep: str
             f'[build-system]\nrequires=["setuptools"]\nbuild-backend="setuptools.build_meta"\n'
             f'[project]\nname="{name}"\nversion="0.0.1"\n{dep}[project.scripts]\n{eps}'
             f'[tool.setuptools.packages.find]\nwhere=["."]\n')
-        subprocess.run([str(self.trusted), "-m", "pip", "wheel", "--no-build-isolation", "--no-deps",
+        # Build the synthetic test wheels with the Gate 0 development
+        # environment. The trusted parent is intentionally a bare CPython on
+        # some supported hosts, including setup-python, and is tested as such by
+        # the real installer path below. Requiring a build backend in that bare
+        # parent makes every test fail during fixture setup before the installer
+        # is exercised. The development environment pins setuptools, so this
+        # remains reproducible and offline after provisioning.
+        subprocess.run([sys.executable, "-m", "pip", "wheel", "--no-build-isolation", "--no-deps",
                         "-w", str(self.wheelhouse), str(src)], check=True, capture_output=True)
         return next(self.wheelhouse.glob(f"{name.replace('-', '_')}-*.whl"))
 

tests/test_gate0.py

@@ -5674,9 +5674,13 @@ def _crash_public_start(self, role: str, run_id: str):
             "from test_gate0 import _StubEngine\n"
             "class _LongRunning(_StubEngine):\n"
             "    def operate_argv(self, _cfg, *, dry_run=False):\n"
-            # A detached descendant plus a foreground process: killing the launcher
-            # leaves the descendant behind exactly as a real crash would.
-            "        return ['/bin/sh', '-c', 'sleep 90 & sleep 120']\n"
+            # Run through the verified generation's regular-file interpreter, just
+            # like every production adapter runs a verified venv entrypoint. Using
+            # /bin/sh here made the fixture platform-dependent because it is a
+            # symlink on Ubuntu and the runtime correctly refuses symlinked launch
+            # targets with O_NOFOLLOW.
+            "        body = 'import os,time\\nif os.fork() == 0: time.sleep(90)\\ntime.sleep(120)'\n"
+            "        return [str(self.verified.bin('python')), '-c', body]\n"
             "    def operate_env(self, _cfg):\n"
             "        return {}\n"
             "    def child_env(self, _cfg=None):\n"
@@ -6548,7 +6552,11 @@ def _public_start(self, role: str, run_id: str, body: str):
             "from test_gate0 import _StubEngine\n"
             "class _Detaching(_StubEngine):\n"
             "    def operate_argv(self, _cfg, *, dry_run=False):\n"
-            f"        return ['/usr/bin/python3', '-c', {body!r}, "
+            # Keep the fixture inside the same verified-generation boundary as the
+            # production adapters. /usr/bin/python3 is normally a symlink on
+            # Debian and Ubuntu, while signed release entrypoints are required to
+            # be regular files before a generation is admitted.
+            f"        return [str(self.verified.bin('python')), '-c', {body!r}, "
             f"{str(self.home / 'detached.pid')!r}]\n"
             "    def operate_env(self, _cfg):\n"
             "        return {}\n"
@@ -6584,7 +6592,11 @@ def test_a_detached_child_blocks_stop_deletion_and_a_second_start(self):
             if ownership is not None and ownership.spawn_state == run_state.SPAWN_OWNED:
                 break
             if launcher.poll() is not None:
-                self.fail(f"the public start exited early: {launcher.stderr.read()[:900]}")
+                self.fail(
+                    "the public start exited early: "
+                    f"stdout={launcher.stdout.read()[:900]} "
+                    f"stderr={launcher.stderr.read()[:900]}"
+                )
             time.sleep(0.1)
         self.assertIsNotNone(ownership)