diff --git a/scripts/glaeda-cmux-runner-hook b/scripts/glaeda-cmux-runner-hook
index 97f80bffc..a8d4bdb19 100755
--- a/scripts/glaeda-cmux-runner-hook
+++ b/scripts/glaeda-cmux-runner-hook
@@ -458,6 +458,9 @@ EXCLUSIVE_UNITS = 1 << 16
 EXCLUSIVE_CLASS = "exclusive"
 EXCLUSIVE_CAPACITY_WAIT_S = 300.0  # NIGHTLY_CAPACITY_WAIT_S: the same owned-pool rescue window
 JOB_CLAIM_ENV = "GLAEDA_JOB_CLAIM"
+# The sha256 of this hook file, written beside JOB_CLAIM_ENV: a job that holds the whole mini can tell which hook
+# admitted it (cmux's signing jobs accept only hooks that wait out an earlier job's leftover processes).
+HOOK_SHA_ENV = "GLAEDA_HOOK_SHA256"
 CLASS_COST: dict[str, tuple[int, tuple[str, ...]]] = {
     "compile": (5, ("persistent-dd", "root")), "gui": (1, ("gui", "root")), "product": (1, ("gui", "root")),
     "compile-gui": (4, ("root",)), "gui-step": (1, ("gui", "root")),
@@ -2023,9 +2026,10 @@ def export_developer_dir(xcode_app: str) -> str:
 
 
 def export_job_claim(capacity_units: int, taken: dict[str, Any], note: str) -> str:
-    """Tell an admitted job, through $GITHUB_ENV, that it holds the whole mini (JOB_CLAIM_ENV=exclusive): an exclusive
-    class job that holds every capacity unit, or any job holding the fleet host lock itself (a mini without weighted
-    capacity). Nothing for any other job, and nothing when there is no $GITHUB_ENV. Returns a note, or ''."""
+    """Tell an admitted job, through $GITHUB_ENV, that it holds the whole mini (JOB_CLAIM_ENV=exclusive) and which
+    hook admitted it (HOOK_SHA_ENV, this file's sha256): an exclusive class job that holds every capacity unit, or any
+    job holding the fleet host lock itself (a mini without weighted capacity). Nothing for any other job, and nothing
+    when there is no $GITHUB_ENV. Returns a note, or ''."""
     if capacity_units > 0:
         whole = taken.get("class") == EXCLUSIVE_CLASS and taken.get("units") == capacity_units
     else:
@@ -2034,8 +2038,11 @@ def export_job_claim(capacity_units: int, taken: dict[str, Any], note: str) -> s
     if not whole or not target:
         return ""
     with contextlib.suppress(OSError):
+        lines = f"{JOB_CLAIM_ENV}={EXCLUSIVE_CLASS}\n"
+        with contextlib.suppress(OSError):  # an unreadable hook writes no sha, and a job that needs one refuses itself
+            lines += f"{HOOK_SHA_ENV}={hashlib.sha256(Path(__file__).resolve().read_bytes()).hexdigest()}\n"
         with open(target, "a", encoding="utf-8") as env_file:
-            env_file.write(f"{JOB_CLAIM_ENV}={EXCLUSIVE_CLASS}\n")
+            env_file.write(lines)
         return f"{JOB_CLAIM_ENV}={EXCLUSIVE_CLASS} for the job (it holds the whole mini)"
     return ""
 
diff --git a/scripts/glaeda-disk b/scripts/glaeda-disk
index afab5d98d..909bd5c8e 100755
--- a/scripts/glaeda-disk
+++ b/scripts/glaeda-disk
@@ -843,6 +843,7 @@ CMUX_NEXT_DRAIN_HOOK_SHA256 = frozenset({
     "33deff2a5a3a025cc542678e7a856eae0e5ca7932e4549c0b230add25e86d482",
     "fb0442d31e23f01326118b7d6be2effd0ba91bff9a0b59c62016c39bc23116da",
     "2695209c13db5fe7514daf76d3e8e547b9569ad9a545225e52f7e07dd83d69e4",
+    "41e29cd9dca8cdee88ce069b61956674bb79c2c3da90af5520e3e397bfbedeef",
 })
 CMUX_NEXT_CI_PRESERVED_NAMES = frozenset({
     "SourcePackages", "ModuleCache.noindex", "SDKStatCaches.noindex",
diff --git a/scripts/test-glaeda-cmux-runner.py b/scripts/test-glaeda-cmux-runner.py
index ca8e038ed..72df2e8a6 100644
--- a/scripts/test-glaeda-cmux-runner.py
+++ b/scripts/test-glaeda-cmux-runner.py
@@ -2046,6 +2046,8 @@ def test_a_signing_job_takes_the_whole_mini(self) -> None:
                           admitted.stdout)
             self.assertIn("GLAEDA_JOB_CLAIM=exclusive for the job", admitted.stdout)
             self.assertIn("GLAEDA_JOB_CLAIM=exclusive\n", github_env.read_text())
+            self.assertIn(f"GLAEDA_HOOK_SHA256={hashlib.sha256(HOOK.read_bytes()).hexdigest()}\n",
+                          github_env.read_text(), "the admitted job learns which hook admitted it")
             for name, runner in (("swift-package-tests", "s1"), ("verify-signed-nightly", "s2")):
                 beside = self.job(name, runner, 14, None, "--gui-wait", "0")
                 self.assertEqual(beside.returncode, 1, beside.stdout + beside.stderr)
@@ -2164,9 +2166,16 @@ def test_job_claim_names_only_a_whole_mini(self) -> None:
             self.assertFalse(github_env.exists())
             self.assertIn("holds the whole mini", hook.export_job_claim(14, {"class": "exclusive", "units": 14}, ""))
             self.assertIn("holds the whole mini", hook.export_job_claim(0, {}, f"{hook.HOST_LOCK_HELD} (held)"))
-        self.assertEqual(github_env.read_text(), "GLAEDA_JOB_CLAIM=exclusive\n" * 2)
+        claim = f"GLAEDA_JOB_CLAIM=exclusive\nGLAEDA_HOOK_SHA256={hashlib.sha256(HOOK.read_bytes()).hexdigest()}\n"
+        self.assertEqual(github_env.read_text(), claim * 2, "the claim names the hook that admitted the job")
         with mock.patch.dict(os.environ, {}, clear=True):
             self.assertEqual(hook.export_job_claim(14, {"class": "exclusive", "units": 14}, ""), "")
+        github_env.unlink()
+        with mock.patch.dict(os.environ, {"GITHUB_ENV": os.fspath(github_env)}), \
+                mock.patch.object(hook, "__file__", os.fspath(self.dir / "no-such-hook")):
+            self.assertIn("holds the whole mini", hook.export_job_claim(14, {"class": "exclusive", "units": 14}, ""))
+        self.assertEqual(github_env.read_text(), "GLAEDA_JOB_CLAIM=exclusive\n",
+                         "a hook that cannot read itself names no sha, so a job that needs one refuses itself")
 
     def test_a_nightly_sign_or_verify_job_needs_no_compile_tokens(self) -> None:
         """nightly.yml's sign and verify jobs were unknown jobs, so compiles: first in line, they still waited for the