Fix cost/egg window to use later of first egg or first feed event

When egg data is imported but feed data starts later, cost/egg was
incorrectly using the egg window (e.g., 30 days) instead of the
period where both data types exist. Now cost/egg uses max(first_egg,
first_feed) to ensure accurate cost calculation.

Each metric now displays its own window: "4.7 eggs/day (30d) | €0.28/egg (7d)"

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

src/animaltrack/web/routes/eggs.py

@@ -184,7 +184,8 @@ def _get_global_cost_per_egg(db: Any, now_ms: int) -> tuple[float | None, int]:
     """Calculate global cost per egg over dynamic window.
 
     Aggregates feed costs and egg counts across all locations.
-    Uses a dynamic window based on the first egg collection event.
+    Uses a dynamic window based on the later of first egg event or first feed event,
+    ensuring we only calculate cost for periods with complete data.
 
     Args:
         db: Database connection.
@@ -195,9 +196,22 @@ def _get_global_cost_per_egg(db: Any, now_ms: int) -> tuple[float | None, int]:
     """
     from animaltrack.events import FEED_GIVEN
 
-    # Calculate dynamic window based on first egg event
+    # Calculate dynamic window based on the later of first egg or first feed event
+    # This ensures we only calculate cost/egg for periods with both data types
     first_egg_ts = _get_first_event_ts(db, "ProductCollected", product_prefix="egg.")
-    window_start, window_end, window_days = _calculate_window(now_ms, first_egg_ts)
+    first_feed_ts = _get_first_event_ts(db, "FeedGiven")
+
+    # Use the later timestamp (max) to ensure complete data for both metrics
+    if first_egg_ts is None and first_feed_ts is None:
+        first_event_ts = None
+    elif first_egg_ts is None:
+        first_event_ts = first_feed_ts
+    elif first_feed_ts is None:
+        first_event_ts = first_egg_ts
+    else:
+        first_event_ts = max(first_egg_ts, first_feed_ts)
+
+    window_start, window_end, window_days = _calculate_window(now_ms, first_event_ts)
 
     event_store = EventStore(db)
 
@@ -300,17 +314,18 @@ def _get_eggs_display_data(db: Any, locations: list) -> dict:
 
     Returns:
         Dict with harvest_events, sell_events, eggs_per_day, cost_per_egg,
-        eggs_window_days, sales_stats, location_names.
+        eggs_window_days, cost_window_days, sales_stats, location_names.
     """
     now_ms = int(time.time() * 1000)
     eggs_per_day, eggs_window_days = _get_eggs_per_day(db, now_ms)
-    cost_per_egg, _ = _get_global_cost_per_egg(db, now_ms)
+    cost_per_egg, cost_window_days = _get_global_cost_per_egg(db, now_ms)
     return {
         "harvest_events": _get_recent_events(db, PRODUCT_COLLECTED, limit=10),
         "sell_events": _get_recent_events(db, PRODUCT_SOLD, limit=10),
         "eggs_per_day": eggs_per_day,
         "cost_per_egg": cost_per_egg,
         "eggs_window_days": eggs_window_days,
+        "cost_window_days": cost_window_days,
         "sales_stats": _get_sales_stats(db, now_ms),
         "location_names": {loc.id: loc.name for loc in locations},
     }

src/animaltrack/web/templates/eggs.py

@@ -36,6 +36,7 @@ def eggs_page(
     eggs_per_day: float | None = None,
     cost_per_egg: float | None = None,
     eggs_window_days: int = 30,
+    cost_window_days: int = 30,
     sales_stats: dict | None = None,
     location_names: dict[str, str] | None = None,
     # Field value preservation on errors
@@ -62,7 +63,8 @@ def eggs_page(
         sell_events: Recent ProductSold events (most recent first).
         eggs_per_day: Average eggs per day over window.
         cost_per_egg: Average cost per egg in EUR over window.
-        eggs_window_days: Actual window size in days for the metrics.
+        eggs_window_days: Actual window size in days for eggs_per_day.
+        cost_window_days: Actual window size in days for cost_per_egg.
         sales_stats: Dict with 'total_qty', 'total_cents', and 'avg_price_per_egg_cents'.
         location_names: Dict mapping location_id to location name for display.
         harvest_quantity: Preserved quantity value on error.
@@ -100,6 +102,7 @@ def eggs_page(
                     eggs_per_day=eggs_per_day,
                     cost_per_egg=cost_per_egg,
                     eggs_window_days=eggs_window_days,
+                    cost_window_days=cost_window_days,
                     location_names=location_names,
                     default_quantity=harvest_quantity,
                     default_notes=harvest_notes,
@@ -135,6 +138,7 @@ def harvest_form(
     eggs_per_day: float | None = None,
     cost_per_egg: float | None = None,
     eggs_window_days: int = 30,
+    cost_window_days: int = 30,
     location_names: dict[str, str] | None = None,
     default_quantity: str | None = None,
     default_notes: str | None = None,
@@ -149,7 +153,8 @@ def harvest_form(
         recent_events: Recent (Event, is_deleted) tuples, most recent first.
         eggs_per_day: Average eggs per day over window.
         cost_per_egg: Average cost per egg in EUR over window.
-        eggs_window_days: Actual window size in days for the metrics.
+        eggs_window_days: Actual window size in days for eggs_per_day.
+        cost_window_days: Actual window size in days for cost_per_egg.
         location_names: Dict mapping location_id to location name for display.
         default_quantity: Preserved quantity value on error.
         default_notes: Preserved notes value on error.
@@ -193,13 +198,13 @@ def harvest_form(
         loc_name = location_names.get(loc_id, "Unknown")
         return f"{quantity} eggs from {loc_name}", event.id
 
-    # Build stats text - combine eggs/day and cost/egg
+    # Build stats text - each metric shows its own window
     stat_parts = []
     if eggs_per_day is not None:
-        stat_parts.append(f"{eggs_per_day:.1f} eggs/day")
+        stat_parts.append(f"{eggs_per_day:.1f} eggs/day ({eggs_window_days}d)")
     if cost_per_egg is not None:
-        stat_parts.append(f"€{cost_per_egg:.3f}/egg cost")
+        stat_parts.append(f"€{cost_per_egg:.3f}/egg ({cost_window_days}d)")
-    stat_text = " | ".join(stat_parts) + f" ({eggs_window_days}-day avg)" if stat_parts else None
+    stat_text = " | ".join(stat_parts) if stat_parts else None
 
     form = Form(
         H2("Harvest Eggs", cls="text-xl font-bold mb-4"),