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: