fix: preserve cost submenu availability transitions

Author: steipete

Sources/CodexBar/CostHistoryChartMenuView.swift

@@ -774,6 +774,7 @@ extension CostHistoryChartMenuView {
         let historyDays: Int
         let windowLabel: String?
         let totalCostBitPattern: UInt64?
+        let hasDailyEntries: Bool
         let daily: [VisibleDailyFingerprint]
         let projects: [VisibleProjectFingerprint]
     }
@@ -822,6 +823,7 @@ extension CostHistoryChartMenuView {
             historyDays: snapshot.historyDays,
             windowLabel: snapshot.historyLabel,
             totalCostBitPattern: snapshot.last30DaysCostUSD.map(\.bitPattern),
+            hasDailyEntries: !snapshot.daily.isEmpty,
             daily: snapshot.daily
                 .filter { self.chartPointInput(for: $0) != nil }
                 .sorted { $0.date < $1.date }

Tests/CodexBarTests/CostHistoryChartMenuViewTests.swift

@@ -466,8 +466,8 @@ struct CostHistoryChartMenuViewTests {
         ]
         let empty = Self.fingerprint(daily: [])
 
-        #expect(Self.fingerprint(daily: invalidRows) == empty)
-        #expect(Self.fingerprint(daily: differentInvalidRows) == empty)
+        #expect(Self.fingerprint(daily: invalidRows) == Self.fingerprint(daily: differentInvalidRows))
+        #expect(Self.fingerprint(daily: invalidRows) != empty)
         #expect(Self.fingerprint(daily: [Self.dailyEntry(date: "2026-06-07", costUSD: 1)]) != empty)
     }