diff --git a/gateway/restart.py b/gateway/restart.py
index 8e31ab713b..a4a5bcee6c 100644
--- a/gateway/restart.py
+++ b/gateway/restart.py
@@ -358,6 +358,9 @@ def resolve_systemd_timeout_stop_sec(
 def resolve_restart_exit_wait_budget(
     drain_timeout: float, after_turn_timeout: float, cron_drain_timeout: float = 0.0, *, headroom: float = 15.0,
 ) -> float:
-    """Seconds a CLI should wait for the gateway PID to exit after SIGUSR1: in-band restart may
-    defer ``stop()`` until turns finish, then spend the longer chat or cron drain inside it."""
-    return max(_seconds(drain_timeout), _seconds(cron_drain_timeout)) + _seconds(after_turn_timeout) + _seconds(headroom)
+    """Observer budget for in-band deferral, the full stop envelope, and replacement startup.
+
+    The stop envelope includes cron cleanup reserve, supervisor headroom and the floor;
+    deferral precedes it, while observer headroom follows it. Cron zero opts out.
+    """
+    return _seconds(after_turn_timeout) + resolve_systemd_timeout_stop_sec(drain_timeout, cron_drain_timeout) + _seconds(headroom)
diff --git a/tests/gateway/test_restart_after_turn.py b/tests/gateway/test_restart_after_turn.py
index dd06e69515..b79a8b0cf1 100644
--- a/tests/gateway/test_restart_after_turn.py
+++ b/tests/gateway/test_restart_after_turn.py
@@ -4,6 +4,7 @@ from gateway.restart import (
     DEFAULT_GATEWAY_RESTART_AFTER_TURN_TIMEOUT,
     parse_restart_after_turn_timeout,
     resolve_restart_exit_wait_budget,
+    resolve_systemd_timeout_stop_sec,
 )
 from gateway.run import GatewayRunner
 
@@ -20,12 +21,15 @@ def test_parse_restart_after_turn_timeout_defaults_and_clamps():
 
 
 def test_resolve_restart_exit_wait_budget_covers_both_phases():
-    assert resolve_restart_exit_wait_budget(0, 0, headroom=15) == 15.0
-    assert resolve_restart_exit_wait_budget(180, 21600, headroom=15) == 180 + 21600 + 15
-    assert resolve_restart_exit_wait_budget(2, 3, 80, headroom=15) == 3 + 80 + 15
-    assert resolve_restart_exit_wait_budget(80, 3, 2, headroom=15) == 3 + 80 + 15
-    assert resolve_restart_exit_wait_budget(2, 3, 0, headroom=15) == 3 + 2 + 15
-    assert resolve_restart_exit_wait_budget("bad", "bad", headroom="x") == 0.0
+    assert resolve_restart_exit_wait_budget(0, 0, 0, headroom=15) == resolve_systemd_timeout_stop_sec(0, 0) + 15
+    assert resolve_restart_exit_wait_budget(180, 21600, 0, headroom=15) == 21600 + resolve_systemd_timeout_stop_sec(180, 0) + 15
+    for chat, cron in ((2, 80), (80, 2), (2, 0), (0, 0)):
+        stop_envelope = resolve_systemd_timeout_stop_sec(chat, cron)
+        assert resolve_restart_exit_wait_budget(chat, 3, cron, headroom=15) == 3 + stop_envelope + 15
+    # A bounded observer uses the longer stop path, not the sum of independent drains.
+    assert resolve_restart_exit_wait_budget(80, 3, 80, headroom=15) == 3 + resolve_systemd_timeout_stop_sec(80, 80) + 15
+    assert resolve_restart_exit_wait_budget(2, 3, 0, headroom=15) < resolve_restart_exit_wait_budget(2, 3, 80, headroom=15)
+    assert resolve_restart_exit_wait_budget("bad", "bad", 0, headroom="x") == 60.0
 
 
 def test_cli_restart_wait_covers_configured_cron_drain(tmp_path, monkeypatch):
@@ -38,7 +42,12 @@ def test_cli_restart_wait_covers_configured_cron_drain(tmp_path, monkeypatch):
         "agent:\n  restart_drain_timeout: 2\n  restart_after_turn_timeout: 3\n  cron_drain_timeout: 80\n",
         encoding="utf-8",
     )
-    assert gateway_cli._get_restart_exit_wait_budget() >= 3 + 80 + 15
+    assert gateway_cli._get_restart_exit_wait_budget() == 3 + resolve_systemd_timeout_stop_sec(2, 80) + 15
+    (tmp_path / "config.yaml").write_text(
+        "agent:\n  restart_drain_timeout: 2\n  restart_after_turn_timeout: 3\n  cron_drain_timeout: 0\n",
+        encoding="utf-8",
+    )
+    assert gateway_cli._get_restart_exit_wait_budget() == 3 + resolve_systemd_timeout_stop_sec(2, 0) + 15
 
 
 def test_load_restart_after_turn_timeout_preserves_zero(tmp_path, monkeypatch):