Fix biweekly slot sharing: max 2 per slot + calendar week offset

- Mark biweekly slots as fully used (in used_times) after 2nd meeting is
  placed, preventing 3rd/4th meetings from being scheduled in same slot
- Calendar: biweekly events sharing a slot get week_offset so they
  alternate (1st starts week 1, 2nd starts week 2)

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: jeremymanning

cdl_bot/services/calendar_service.py

@@ -254,6 +254,7 @@ def create_recurring_event(
         term_end: str,
         location: str = PROJECT_LOCATION,
         is_biweekly: bool = False,
+        week_offset: int = 0,
         attendee_emails: Optional[list] = None,
         description: str = "",
     ) -> tuple[bool, Optional[str], Optional[str]]:
@@ -270,6 +271,8 @@ def create_recurring_event(
             term_end: Term end date "YYYY-MM-DD"
             location: Event location string
             is_biweekly: If True, event repeats every 2 weeks
+            week_offset: Number of weeks to offset the start (for alternating
+                         biweekly meetings sharing the same slot)
             attendee_emails: Optional list of attendee email addresses
             description: Optional event description
 
@@ -288,6 +291,10 @@ def create_recurring_event(
             days_ahead += 7
         first_date = start_date + timedelta(days=days_ahead)
 
+        # Offset for alternating biweekly meetings sharing the same slot
+        if week_offset:
+            first_date += timedelta(weeks=week_offset)
+
         # Build RRULE
         end_date = date.fromisoformat(term_end)
         until_str = end_date.strftime("%Y%m%dT235959Z")
@@ -356,6 +363,10 @@ def create_schedule_events(
         if schedule_df is None or schedule_df.empty:
             return results
 
+        # Track biweekly slots to offset alternating meetings
+        # Key: (day, start_time) -> count of biweekly meetings already placed
+        biweekly_slot_count = {}
+
         for meeting_name, row in schedule_df.iterrows():
             day = row["Day"]
             start = row["Start Time"][:5]
@@ -366,6 +377,15 @@ def create_schedule_events(
             is_individual = meeting_name.endswith(" one-on-one")
             location = INDIVIDUAL_LOCATION if is_individual else PROJECT_LOCATION
 
+            # For biweekly meetings, check if another biweekly already occupies
+            # this slot and offset by 1 week so they alternate
+            week_offset = 0
+            if is_biweekly:
+                slot_key = (day, start)
+                count = biweekly_slot_count.get(slot_key, 0)
+                week_offset = count  # 0 for first, 1 for second
+                biweekly_slot_count[slot_key] = count + 1
+
             success, error, event_id = self.create_recurring_event(
                 calendar_id=calendar_id,
                 summary=meeting_name,
@@ -376,6 +396,7 @@ def create_schedule_events(
                 term_end=term_end,
                 location=location,
                 is_biweekly=is_biweekly,
+                week_offset=week_offset,
             )
 
             results.append({

cdl_bot/services/scheduling_service.py

@@ -100,7 +100,8 @@ def calculate_pi_time_score(day, block_times, current_day_blocks, days_with_meet
     # Tracking state
     scheduled = {}
     used_times = set()
-    biweekly_times = {}
+    biweekly_times = {}  # (day, time) -> first meeting name
+    biweekly_full = set()  # (day, time) slots that already have 2 biweekly meetings
     meeting_end_times = {}
     days_with_meetings = set()
     day_meeting_blocks = defaultdict(list)
@@ -165,6 +166,9 @@ def process_meeting(meeting_name, group_members, is_biweekly_meeting=False):
                 else:
                     if any(t in used_times for t in block_index):
                         continue
+                    # Slot already has 2 biweekly meetings — full
+                    if any(t in biweekly_full for t in block_index):
+                        continue
                     overlapping = [biweekly_times[t] for t in block_index if t in biweekly_times]
                     if overlapping:
                         unique_overlapping = set(overlapping)
@@ -263,7 +267,15 @@ def schedule_meeting(meeting_name, group_members, is_biweekly_meeting):
 
         if is_biweekly_meeting:
             for t in best["times"]:
-                biweekly_times[(best["day"], t)] = meeting_name
+                slot = (best["day"], t)
+                if slot in biweekly_times:
+                    # 2nd biweekly meeting — slot is now full (2 alternating weeks used)
+                    biweekly_full.add(slot)
+                    # Also add to used_times so no further meetings (weekly OR biweekly)
+                    # can be placed here
+                    used_times.add(slot)
+                else:
+                    biweekly_times[slot] = meeting_name
         else:
             for t in best["times"]:
                 used_times.add((best["day"], t))