diff --git a/CHANGELOG.md b/CHANGELOG.md
index 941c61ea..7539fc3b 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -2,6 +2,10 @@
 
 ## [Unreleased]
 
+### Fixed
+
+- **PR #2582** by @Michaelyklam (refs #2577) — Harden embedded workspace-terminal shell cleanup so graceful WebUI shutdowns close/reap every active PTY shell and the spawned shell receives a Linux parent-death signal if the WebUI process dies. The terminal close path now waits again after SIGKILL so timed-out shells do not remain unreaped.
+
 
 ## [v0.51.92] — 2026-05-19 — Release BP (stage-385 — 7-PR full sweep batch — RFC Slice 3c clarification + workspace tree icon alignment + project move cache refresh + auto-compression handoff metadata + Grok OAuth provider catalog + anonymous custom endpoint picker fallback + PWA standalone reload + pull-to-refresh)
 
diff --git a/api/terminal.py b/api/terminal.py
index 47d88abb..5ac2c741 100644
--- a/api/terminal.py
+++ b/api/terminal.py
@@ -9,6 +9,7 @@ in the agent execution layer.
 from __future__ import annotations
 
 import errno
+import atexit
 import codecs
 import fcntl
 import os
@@ -69,6 +70,20 @@ _TERMINALS: dict[str, TerminalSession] = {}
 _LOCK = threading.RLock()
 
 
+def _terminal_shell_preexec_fn() -> None:
+    """Ask Linux to terminate the PTY shell when the WebUI parent dies."""
+    try:
+        import ctypes
+
+        libc = ctypes.CDLL(None)
+        libc.prctl(1, signal.SIGTERM)  # PR_SET_PDEATHSIG=1, SIGTERM=15
+    except Exception:
+        # Non-Linux platforms or restricted runtimes should still be able to
+        # open an embedded terminal; they just do not get the Linux pdeathsig
+        # hardening.
+        pass
+
+
 def _decode_terminal_output(decoder, data: bytes) -> str:
     """Decode PTY bytes without stripping terminal control sequences."""
     return decoder.decode(data)
@@ -178,6 +193,7 @@ def start_terminal(session_id: str, workspace: Path, rows: int = 24, cols: int =
             stdout=slave_fd,
             stderr=slave_fd,
             close_fds=True,
+            preexec_fn=_terminal_shell_preexec_fn,
             start_new_session=True,
         )
         os.close(slave_fd)
@@ -240,9 +256,24 @@ def close_terminal(session_id: str) -> bool:
                     os.killpg(term.proc.pid, signal.SIGKILL)
                 except ProcessLookupError:
                     pass
+                try:
+                    term.proc.wait(timeout=1.0)
+                except (subprocess.TimeoutExpired, ProcessLookupError):
+                    pass
     finally:
         try:
             os.close(term.master_fd)
         except OSError:
             pass
     return True
+
+
+def close_all_terminals() -> None:
+    """Best-effort reap of embedded shells during graceful WebUI shutdown."""
+    with _LOCK:
+        session_ids = list(_TERMINALS)
+    for session_id in session_ids:
+        close_terminal(session_id)
+
+
+atexit.register(close_all_terminals)
diff --git a/tests/test_terminal_process_cleanup.py b/tests/test_terminal_process_cleanup.py
new file mode 100644
index 00000000..51607935
--- /dev/null
+++ b/tests/test_terminal_process_cleanup.py
@@ -0,0 +1,103 @@
+import subprocess
+
+import api.terminal as terminal
+
+
+class _DummyThread:
+    def __init__(self, *args, **kwargs):
+        self.args = args
+        self.kwargs = kwargs
+        self.started = False
+
+    def start(self):
+        self.started = True
+
+
+class _FakeProc:
+    pid = 999_999_999
+
+    def __init__(self):
+        self.wait_calls = []
+
+    def poll(self):
+        return None
+
+    def wait(self, timeout=None):
+        self.wait_calls.append(timeout)
+        return 0
+
+
+def test_terminal_shell_uses_parent_death_signal_preexec(monkeypatch, tmp_path):
+    captured = {}
+    proc = _FakeProc()
+
+    def fake_popen(*args, **kwargs):
+        captured["args"] = args
+        captured["kwargs"] = kwargs
+        return proc
+
+    monkeypatch.setattr(terminal.subprocess, "Popen", fake_popen)
+    monkeypatch.setattr(terminal.threading, "Thread", _DummyThread)
+    monkeypatch.setattr(terminal, "_set_size", lambda *args, **kwargs: None)
+
+    term = terminal.start_terminal("term-preexec", tmp_path)
+
+    try:
+        assert term.proc is proc
+        assert captured["kwargs"]["preexec_fn"] is terminal._terminal_shell_preexec_fn
+        assert captured["kwargs"]["start_new_session"] is True
+        assert captured["kwargs"]["stdin"] == captured["kwargs"]["stdout"] == captured["kwargs"]["stderr"]
+    finally:
+        terminal.close_terminal("term-preexec")
+
+
+def test_close_terminal_waits_again_after_sigkill(monkeypatch):
+    class TimeoutThenReapedProc(_FakeProc):
+        def wait(self, timeout=None):
+            self.wait_calls.append(timeout)
+            if len(self.wait_calls) == 1:
+                raise subprocess.TimeoutExpired(cmd="shell", timeout=timeout)
+            return -9
+
+    proc = TimeoutThenReapedProc()
+    term = terminal.TerminalSession(
+        session_id="term-timeout",
+        workspace="/tmp",
+        proc=proc,
+        master_fd=12345,
+    )
+    terminal._TERMINALS["term-timeout"] = term
+    kills = []
+    monkeypatch.setattr(terminal.os, "killpg", lambda pid, sig: kills.append((pid, sig)))
+    monkeypatch.setattr(terminal.os, "close", lambda fd: None)
+
+    assert terminal.close_terminal("term-timeout") is True
+
+    assert proc.wait_calls == [1.5, 1.0]
+    assert kills == [(proc.pid, terminal.signal.SIGHUP), (proc.pid, terminal.signal.SIGKILL)]
+
+
+def test_close_all_terminals_closes_snapshot(monkeypatch):
+    terminal._TERMINALS.clear()
+    terminal._TERMINALS.update({"a": object(), "b": object()})
+    closed = []
+
+    def fake_close(session_id):
+        closed.append(session_id)
+        terminal._TERMINALS.pop(session_id, None)
+        return True
+
+    monkeypatch.setattr(terminal, "close_terminal", fake_close)
+
+    terminal.close_all_terminals()
+
+    assert closed == ["a", "b"]
+    assert terminal._TERMINALS == {}
+
+
+def test_terminal_module_registers_graceful_shutdown_reaper():
+    src = terminal.Path(terminal.__file__).read_text()
+
+    assert "atexit.register(close_all_terminals)" in src
+    assert "preexec_fn=_terminal_shell_preexec_fn" in src
+    assert "libc.prctl(1, signal.SIGTERM)" in src