diff --git a/pyproject.toml b/pyproject.toml
index ebf044f8..bd46a634 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -79,6 +79,11 @@ testing = [
   # https://docs.pytest.org/en/8.0.x/explanation/goodpractices.html#choosing-a-test-layout-import-rules
   "pytest>=8.3.5",
   "pexpect>=4.9.0,<5",
+  # per-test wall-clock bound (used via
+  # `@pytest.mark.timeout(..., method='thread')` on the
+  # known-hanging `subint`-backend audit tests; see
+  # `ai/conc-anal/subint_*_issue.md`).
+  "pytest-timeout>=2.3",
 ]
 repl = [
   "pyperclip>=1.9.0",
diff --git a/tests/discovery/test_registrar.py b/tests/discovery/test_registrar.py
index 6f34b117..bd015608 100644
--- a/tests/discovery/test_registrar.py
+++ b/tests/discovery/test_registrar.py
@@ -517,6 +517,22 @@ async def kill_transport(
 
 
 # @pytest.mark.parametrize('use_signal', [False, True])
+#
+# Wall-clock bound via `pytest-timeout` (`method='thread'`).
+# Under `--spawn-backend=subint` this test can wedge in an
+# un-Ctrl-C-able state (abandoned-subint + shared-GIL
+# starvation → signal-wakeup-fd pipe fills → SIGINT silently
+# dropped; see `ai/conc-anal/subint_sigint_starvation_issue.md`).
+# `method='thread'` is specifically required because `signal`-
+# method SIGALRM suffers the same GIL-starvation path and
+# wouldn't fire the Python-level handler.
+# At timeout the plugin hard-kills the pytest process — that's
+# the intended behavior here; the alternative is an unattended
+# suite run that never returns.
+@pytest.mark.timeout(
+    3,  # NOTE should be a 2.1s happy path.
+    method='thread',
+)
 def test_stale_entry_is_deleted(
     debug_mode: bool,
     daemon: subprocess.Popen,
diff --git a/tests/test_subint_cancellation.py b/tests/test_subint_cancellation.py
index 04b6cc9e..18cbf78b 100644
--- a/tests/test_subint_cancellation.py
+++ b/tests/test_subint_cancellation.py
@@ -161,6 +161,20 @@ def test_subint_happy_teardown(
         trio.run(partial(_happy_path, reg_addr, deadline))
 
 
+# Wall-clock bound via `pytest-timeout` (`method='thread'`)
+# as defense-in-depth over the inner `trio.fail_after(15)`.
+# Under the orphaned-channel hang class described in
+# `ai/conc-anal/subint_cancel_delivery_hang_issue.md`, SIGINT
+# is still deliverable and this test *should* be unwedgeable
+# by the inner trio timeout — but sibling subint-backend
+# tests in this repo have also exhibited the
+# `subint_sigint_starvation_issue.md` GIL-starvation flavor,
+# so `method='thread'` keeps us safe in case ordering or
+# load shifts the failure mode.
+@pytest.mark.timeout(
+    3,  # NOTE never passes pre-3.14+ subints support.
+    method='thread',
+)
 def test_subint_non_checkpointing_child(
     reg_addr: tuple[str, int|str],
 ) -> None: