fix(mcp): list_maintenance_plans reports only a slot that fired as last_slot_at (#5863)

A new plan's last_slot_at holds the moment it was made, so its first
slot is the next one; the tool returned that moment, a Wednesday
evening for a Sunday plan, beside latest_run: null. cadence.fired_slot
returns it only when it falls on one of the plan's slots.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

plugins/host_agent/cadence.py

@@ -55,6 +55,16 @@ def last_slot(plan, now: datetime) -> datetime:
     return slot.astimezone(timezone.utc)
 
 
+def fired_slot(plan) -> datetime | None:
+    """The last slot that fired, or None while none has. A new plan's
+    last_slot_at holds the moment it was made, so its first slot is the
+    next one rather than one already past; that moment is no slot (#5863)."""
+    at = plan.last_slot_at
+    if at is None:
+        return None
+    return at if last_slot(plan, at) == at else None
+
+
 def next_slot(plan, now: datetime) -> datetime:
     return last_slot(plan, now) + timedelta(days=7)
 

plugins/host_agent/mcp_tools.py

@@ -136,7 +136,8 @@ async def list_maintenance_plans() -> dict:
 
     A run updates the group's hosts one at a time; `latest_run` says how far
     it got (`hosts_done` of `hosts`), which hosts it passed over and why
-    (`skipped`), and how it ended. get_maintenance_job shows one host's job.
+    (`skipped`), and how it ended. `last_slot_at` is the last scheduled slot
+    that fired, null until one has. get_maintenance_job shows one host's job.
     Plans are created and edited on the Maintenance page.
     """
     from steward.models.ansible_inventory import AnsibleGroup
@@ -164,7 +165,7 @@ async def list_maintenance_plans() -> dict:
             "weekday": cadence.WEEKDAYS[plan.weekday], "at_time": plan.at_time,
             "time_zone": plan.time_zone, "window_minutes": plan.window_minutes,
             "reboot_policy": plan.reboot_policy, "enabled": plan.enabled,
-            "next_slot_at": iso(nxt), "last_slot_at": iso(plan.last_slot_at),
+            "next_slot_at": iso(nxt), "last_slot_at": iso(cadence.fired_slot(plan)),
             "latest_run": None,
         }
         if run:

tests/plugins/host_agent/test_cadence.py

@@ -21,6 +21,16 @@ def _plan(**kw):
     return NS(**base)
 
 
+def test_a_plan_that_has_not_fired_has_no_last_slot():
+    """#5863: a new plan's last_slot_at is the moment it was made, a Wednesday
+    evening for a Sunday plan; only a slot that fired is reported."""
+    made = _plan(time_zone="America/New_York", last_slot_at=datetime(2026, 10, 14, 23, 54, 58, tzinfo=timezone.utc))
+    assert c.fired_slot(made) is None
+    fired = datetime(2026, 10, 18, 7, 0, tzinfo=timezone.utc)      # Sunday 03:00 New York
+    assert c.fired_slot(_plan(time_zone="America/New_York", last_slot_at=fired)) == fired
+    assert c.fired_slot(_plan()) is None
+
+
 def test_the_last_slot_is_the_latest_weekday_and_time_in_the_plans_zone():
     assert c.last_slot(_plan(), NOW) == datetime(2026, 10, 11, 3, 0, tzinfo=timezone.utc)
     # 03:00 in New York is 07:00 UTC in October (EDT)