Update hash seed tests for the module based re exec and add a regression

The existing probe assertions now expect the module flag form. A new
test drives the probe with a launcher stub path that is not even a
real file in place of argv zero, confirming the fix no longer depends
on it being anything runnable, the exact shape of the Windows uv
launcher regression this closes.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_017qfdzgbA5KedGEjD1AayNh

tests/test_pin_hash_seed.py

@@ -56,10 +56,23 @@ def test_reexecs_for_hash_sensitive_commands_when_unset():
     for cmd in ("update", "extract", "cluster-only", "label"):
         outcome = _run_probe(["graphify", cmd, "."])
         assert outcome["called"], f"{cmd} must re-exec with PYTHONHASHSEED pinned"
-        assert outcome["argv"] == [sys.executable, "graphify", cmd, "."]
+        assert outcome["argv"] == [sys.executable, "-m", "graphify", cmd, "."]
         assert outcome["env_hashseed"] == "0"
 
 
+def test_reexec_does_not_depend_on_argv0_being_a_runnable_script():
+    """#3779: a uv/pip/pipx console-script launcher on Windows is a native
+    .exe with no .py content, so `python.exe <that .exe path>` fails
+    outright with "can't open file" the moment argv[0] is replayed as a
+    script path. Re-execing via `-m graphify` never touches argv[0] at
+    all, so a launcher stub that isn't even a real file must not matter."""
+    outcome = _run_probe(["/some/launcher/stub/with/no/py/content", "update", "."])
+    assert outcome["called"]
+    assert outcome["argv"] == [sys.executable, "-m", "graphify", "update", "."], (
+        "the launcher stub path must never appear in the re-exec argv"
+    )
+
+
 def test_does_not_reexec_when_already_set():
     outcome = _run_probe(["graphify", "update", "."], extra_env={"PYTHONHASHSEED": "1"})
     assert not outcome["called"], "an explicit PYTHONHASHSEED must never be overridden"