diff --git a/tests/scripts/desktop_update/test_posix_handoff_pid_export.py b/tests/scripts/desktop_update/test_posix_handoff_pid_export.py
index 9183606e7d..6389b364db 100644
--- a/tests/scripts/desktop_update/test_posix_handoff_pid_export.py
+++ b/tests/scripts/desktop_update/test_posix_handoff_pid_export.py
@@ -1,42 +1,69 @@
-"""The update a POSIX Desktop hand-off spawns is told the marker's live owner as its hand-off pid.
+"""A later generation of a POSIX Desktop hand-off's update adopts the hand-off's own claim.
 
-``hermes update`` adopts an existing claim only when the live owner is its own pid, the
+``hermes update`` adopts an existing claim only when a live partner is its own pid, the
 ``HERMES_UPDATE_HANDOFF_PID`` value, or an ancestor (``update_lock.UpdateLock._is_partner``).
-``posix.sh`` hands marker line 1 to a custodian before any update work starts, and the custodian is
-a sibling of the update child, never an ancestor. On macOS the delegate line cannot rescue it (a
-whole-second creation time never matches the child's own), so a hand-off pid naming the script
-instead of the custodian made every Desktop-initiated update refuse its own claim with exit 2
-(#133992, #134268, #134309, #134381).
+``posix.sh`` hands marker line 1 to a custodian before any update work starts; the custodian is a
+sibling of the update, never an ancestor. The first ``hermes update`` is named on the delegate
+line, but a later generation (a relaunch or a takeover detached from it) has a new pid, so the
+hand-off pid is its only way to recognise the custodian. Naming the script there made those
+updates refuse their own claim with exit 2 (#134268, #134602).
+
+Runs on macOS too (the CI macOS lane), where the marker's creation times come from ``ps`` in
+whole seconds: that host is where the refusal was reported.
 """
 from __future__ import annotations
 
+import json
+from pathlib import Path
+
 import pytest
 
 from tests.scripts.desktop_update.test_desktop_update_posix_marker import FAKE_CLI, _custodian, _install, _run
 
-pytestmark = pytest.mark.platforms("linux")  # /proc creation times, like the rest of the posix marker suite
+pytestmark = pytest.mark.platforms("posix")
 
-RECORD_UPDATE_VIEW = """
-import os, sys
+REPOSITORY = Path(__file__).resolve().parents[3]
+
+# The update child (generation 1) starts generation 2 through an intermediate that exits at once,
+# so generation 2 is reparented away from it (no ancestry to lean on), then waits for its verdict.
+# Generation 2 runs this repository's real UpdateLock against the marker the real posix.sh wrote.
+SECOND_GENERATION = """
+import os, sys, json, subprocess, time
 from pathlib import Path
-if sys.argv[1:2] == ['update']:
-    marker = Path(os.environ['HERMES_HOME']) / '.hermes-update-in-progress'
-    owner = marker.read_text(encoding='utf-8-sig').splitlines()[0]
-    Path(os.environ['HANDOFF_VIEW']).write_text(
-        f"{os.environ.get('HERMES_UPDATE_HANDOFF_PID', '')} {owner}", encoding='utf-8')
+if sys.argv[1:2] == ['update'] and '--help' not in sys.argv:  # not the --keep-stash probe
+    out = Path(os.environ['GEN2_OUT'])
+    probe = (
+        "import json, os, sys; from pathlib import Path\\n"
+        "from hermes_cli.update_lock import UpdateLock, update_marker_path\\n"
+        "lock = UpdateLock(path=update_marker_path())\\n"
+        "ok = lock.acquire()\\n"
+        "Path(sys.argv[1]).write_text(json.dumps({'adopted': ok, 'pid': os.getpid(), "
+        "'holder': lock.holder.pid if lock.holder else None, "
+        "'told': os.environ.get('HERMES_UPDATE_HANDOFF_PID')}), encoding='utf-8')\\n"
+        "ok and lock.release()\\n")
+    env = {k: v for k, v in os.environ.items() if not k.startswith('PYTHON')}
+    env['PYTHONPATH'] = os.environ['GEN2_REPO']
+    subprocess.run([sys.executable, '-c',
+                    'import subprocess, sys; subprocess.Popen(sys.argv[1:], start_new_session=True)',
+                    sys.executable, '-c', probe, str(out)],
+                   cwd=os.environ['GEN2_REPO'], env=env, check=True)
+    deadline = time.monotonic() + 60
+    while not out.exists() and time.monotonic() < deadline:
+        time.sleep(0.05)
+    sys.exit(0 if out.exists() and json.loads(out.read_text(encoding='utf-8-sig'))['adopted'] else 2)
 """
 
 
-def test_the_update_child_is_told_the_live_marker_owner(tmp_path):
+def test_a_later_update_generation_adopts_the_handoffs_claim(tmp_path):
     home, install = _install(tmp_path)
-    (install / "hermes_cli" / "main.py").write_text(RECORD_UPDATE_VIEW + FAKE_CLI, encoding="utf-8")
-    view = tmp_path / "view.txt"
+    (install / "hermes_cli" / "main.py").write_text(SECOND_GENERATION + FAKE_CLI, encoding="utf-8")
+    out = tmp_path / "gen2.json"
 
-    result = _run(tmp_path, home, install, HANDOFF_VIEW=str(view))
+    result = _run(tmp_path, home, install, GEN2_OUT=str(out), GEN2_REPO=str(REPOSITORY))
 
-    assert result.returncode == 0, result.stdout + result.stderr
     custodian = _custodian(home)
     assert custodian, "the hand-off never named a custodian"
-    handoff_pid, owner = view.read_text(encoding="utf-8-sig").split()
-    assert owner == custodian, "line 1 must name the custodian while the update runs"
-    assert handoff_pid == owner, "the update child must be told the marker's owner, not the hand-off script"
+    verdict = json.loads(out.read_text(encoding="utf-8-sig"))
+    assert verdict["adopted"], f"generation 2 refused its own hand-off's claim (holder {verdict['holder']})"
+    assert verdict["told"] == custodian, "the update must be told the marker's owner, not the hand-off script"
+    assert result.returncode == 0, result.stdout + result.stderr