diff --git a/graphify/__main__.py b/graphify/__main__.py
index a2c5416de..730d7a874 100644
--- a/graphify/__main__.py
+++ b/graphify/__main__.py
@@ -528,8 +528,7 @@ def _pin_hash_seed_if_needed() -> None:
         # launcher on Windows is a native .exe with no .py content, so
         # `python.exe <that .exe path>` fails outright with "can't open
         # file" -- every command this function touches (#3779).
-        os.execvpe(
-            sys.executable,
+        _reexec(
             [sys.executable, "-m", "graphify", *sys.argv[1:]],
             {**os.environ, "PYTHONHASHSEED": "0"},
         )
@@ -537,6 +536,26 @@ def _pin_hash_seed_if_needed() -> None:
         pass
 
 
+def _reexec(argv: list[str], env: dict[str, str], windows: bool | None = None) -> None:
+    """Replace the current command with `argv` run under `env`.
+
+    On POSIX this is a real os.execvpe. On Windows os.exec* does not replace
+    the process: CPython spawns a new one and the calling process exits at
+    once, so the caller sees the command "finish" while the work continues
+    detached, and the exiting parent intermittently dies with an access
+    violation (exit 139 / 0xC0000005) instead (#3799). There the child is
+    run with subprocess and waited for, and its exit status is propagated.
+    """
+    if windows is None:
+        windows = os.name == "nt"
+    if windows:
+        import subprocess
+        sys.stdout.flush()
+        sys.stderr.flush()
+        raise SystemExit(subprocess.run(argv, env=env).returncode)
+    os.execvpe(argv[0], argv, env)
+
+
 def main() -> None:
     """Console entry point. Wraps the CLI so that when a downstream consumer closes
     stdout early, graphify treats it as success instead of crashing with an
diff --git a/tests/test_pin_hash_seed.py b/tests/test_pin_hash_seed.py
index 2aad777b5..cd3ec4b27 100644
--- a/tests/test_pin_hash_seed.py
+++ b/tests/test_pin_hash_seed.py
@@ -32,9 +32,9 @@ import sys
 _PROBE = """
 import json, os, sys
 calls = []
-os.execvpe = lambda *a: calls.append(a)
 sys.argv = {argv!r}
 import graphify.__main__ as mainmod
+mainmod._reexec = lambda argv, env: calls.append((argv[0], argv, env))
 mainmod._pin_hash_seed_if_needed()
 print(json.dumps({{"called": bool(calls), "argv": calls[0][1] if calls else None,
                     "env_hashseed": calls[0][2].get("PYTHONHASHSEED") if calls else None}}))
@@ -106,9 +106,9 @@ def test_degrades_instead_of_raising_when_reexec_fails():
 import os, sys
 def _raise(*a):
     raise OSError("exec not permitted")
-os.execvpe = _raise
 sys.argv = ["graphify", "update", "."]
 import graphify.__main__ as mainmod
+mainmod._reexec = _raise
 mainmod._pin_hash_seed_if_needed()  # must not raise
 print("survived")
 """
@@ -137,3 +137,38 @@ def test_update_still_runs_end_to_end_with_hashseed_unset(tmp_path):
 
     assert result.returncode == 0, result.stderr
     assert (tmp_path / "graphify-out" / "graph.json").exists()
+
+
+def test_reexec_uses_execvpe_on_posix(monkeypatch):
+    import graphify.__main__ as mainmod
+    calls = []
+    monkeypatch.setattr(mainmod.os, "execvpe", lambda *a: calls.append(a))
+    mainmod._reexec(["py", "-m", "graphify", "update", "."], {"PYTHONHASHSEED": "0"}, windows=False)
+    assert calls == [("py", ["py", "-m", "graphify", "update", "."], {"PYTHONHASHSEED": "0"})]
+
+
+def test_reexec_waits_and_propagates_exit_code_on_windows(monkeypatch):
+    """#3799: on Windows os.exec* spawns a detached process and the parent
+    exits at once (sometimes with an access violation), so the caller saw
+    the command finish before graph.json was written. The Windows branch
+    must run the child synchronously and exit with the child's status."""
+    import subprocess
+    import graphify.__main__ as mainmod
+    seen = {}
+
+    class _Done:
+        returncode = 3
+
+    def _run(argv, env=None, **kw):
+        seen["argv"], seen["env"] = argv, env
+        return _Done()
+
+    monkeypatch.setattr(subprocess, "run", _run)
+    monkeypatch.setattr(mainmod.os, "execvpe", lambda *a: (_ for _ in ()).throw(AssertionError("execvpe used on Windows")))
+    try:
+        mainmod._reexec(["py", "-m", "graphify", "extract", "."], {"PYTHONHASHSEED": "0"}, windows=True)
+    except SystemExit as e:
+        assert e.code == 3
+    else:
+        raise AssertionError("must exit with the child's return code")
+    assert seen == {"argv": ["py", "-m", "graphify", "extract", "."], "env": {"PYTHONHASHSEED": "0"}}