fix(events): audit pass — 7 correctness fixes across the events system

Backend:
- tools.py: apply UTC normalization to update_event datetime fields
  (matched create_event which already did this)
- events.py service: allow end_dt/recurrence/project_id to be cleared
  via update_event by permitting None for nullable fields
- events.py service: find_events_by_query now returns upcoming events
  first, falling back to past — prevents AI tools from mutating stale
  past events when a future match exists
- events.py service: list_events now uses overlap logic (start <= to
  AND end >= from) so multi-day events spanning the query boundary
  are included; previously only start_dt was checked

Frontend:
- ToolCallCard: fire fable:calendar-changed on created/updated/deleted
  so CalendarView refetches without requiring a manual page refresh
- KnowledgeView: replace raw apiGet('/api/events') with listEvents()
  client function; also fix today bar which was reading .events off a
  flat array (always empty) — now correctly receives EventEntry[]
- HomeView: use full ISO strings for event date range instead of naive
  UTC-midnight strings; deduplicate inline date math via _dateRange()

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

src/fabledassistant/routes/events.py

@@ -96,11 +96,15 @@ async def update_event(event_id: int):
         if int_field in data:
             fields[int_field] = data[int_field]
     for dt_field in ("start_dt", "end_dt"):
-        if dt_field in data and data[dt_field]:
-            try:
-                fields[dt_field] = _parse_dt(data[dt_field])
-            except ValueError:
-                return jsonify({"error": f"Invalid datetime for {dt_field}"}), 400
+        if dt_field in data:
+            if data[dt_field] is None:
+                # Explicit null clears the field (e.g. removing end_dt)
+                fields[dt_field] = None
+            elif data[dt_field]:
+                try:
+                    fields[dt_field] = _parse_dt(data[dt_field])
+                except ValueError:
+                    return jsonify({"error": f"Invalid datetime for {dt_field}"}), 400
     event = await events_svc.update_event(
         user_id=_get_current_user_id(),
         event_id=event_id,

src/fabledassistant/services/events.py

@@ -75,16 +75,24 @@ async def list_events(
     date_from: datetime,
     date_to: datetime,
 ) -> list[Event]:
-    """List events for user_id within [date_from, date_to]."""
+    """List events for user_id that overlap [date_from, date_to].
+
+    An event overlaps the range if it starts before date_to AND either
+    has no end_dt (point event) or its end_dt is after date_from.
+    This ensures multi-day events that span the query boundary are included.
+    """
     async with async_session() as session:
         result = await session.execute(
             select(Event).where(
                 Event.user_id == user_id,
-                Event.start_dt >= date_from,
                 Event.start_dt <= date_to,
+                or_(
+                    Event.end_dt.is_(None),
+                    Event.end_dt >= date_from,
+                ),
             ).order_by(Event.start_dt)
         )
-        return result.scalars().all()
+        return list(result.scalars().all())
 
 
 async def search_events(
@@ -124,8 +132,10 @@ async def update_event(user_id: int, event_id: int, **fields) -> Event | None:
         old_title = event.title  # capture before mutation for CalDAV lookup
         allowed = {"title", "start_dt", "end_dt", "all_day", "description",
                    "location", "color", "recurrence", "project_id"}
+        # Nullable fields that callers can explicitly set to None to clear
+        nullable = {"end_dt", "recurrence", "project_id"}
         for key, value in fields.items():
-            if key in allowed and value is not None:
+            if key in allowed and (value is not None or key in nullable):
                 setattr(event, key, value)
         await session.commit()
         await session.refresh(event)
@@ -153,16 +163,32 @@ async def delete_event(user_id: int, event_id: int) -> None:
 
 
 async def find_events_by_query(user_id: int, query: str) -> list[Event]:
-    """ILIKE search on title — used by AI update/delete tools."""
+    """ILIKE search on title — used by AI update/delete tools.
+
+    Returns upcoming events first (start_dt >= now), falling back to
+    past events so the AI operates on the most relevant match.
+    """
     q = f"%{query}%"
+    now = datetime.now(timezone.utc)
     async with async_session() as session:
-        result = await session.execute(
+        # Prefer events at or after now; fall back to past events
+        upcoming = (await session.execute(
             select(Event).where(
                 Event.user_id == user_id,
                 Event.title.ilike(q),
+                Event.start_dt >= now,
             ).order_by(Event.start_dt)
-        )
-        return result.scalars().all()
+        )).scalars().all()
+        if upcoming:
+            return list(upcoming)
+        past = (await session.execute(
+            select(Event).where(
+                Event.user_id == user_id,
+                Event.title.ilike(q),
+                Event.start_dt < now,
+            ).order_by(Event.start_dt.desc())
+        )).scalars().all()
+        return list(past)
 
 
 # ---------------------------------------------------------------------------

src/fabledassistant/services/tools.py

@@ -1506,7 +1506,10 @@ async def execute_tool(
                 val = arguments.get(key)
                 if val:
                     try:
-                        fields[dt_field] = datetime.fromisoformat(val)
+                        dt = datetime.fromisoformat(val.replace("Z", "+00:00"))
+                        if dt.tzinfo is None:
+                            dt = dt.replace(tzinfo=timezone.utc)
+                        fields[dt_field] = dt
                     except (ValueError, TypeError):
                         return {"success": False, "error": f"Invalid datetime for {key}: {val!r}"}
             updated = await events_update_event(