it("falls back to proportional allocation when utcQuarterHourMessageCounts is absent", () => {

// Session without utcQuarterHourMessageCounts should use forEachSessionHourSlice

const now = Date.now();

const session: UsageSessionEntry = {

key: "fallback-session",

updatedAt: now,

updatedAt: Date.parse("2026-03-15T10:30:00.000Z"),

usage: {

totalTokens: 100,

totalCost: 0.01,

cacheReadCost: 0,

cacheWriteCost: 0,

missingCostEntries: 0,

firstActivity: now - 3600_000,

lastActivity: now,

firstActivity: Date.parse("2026-03-15T10:00:00.000Z"),

lastActivity: Date.parse("2026-03-15T10:30:00.000Z"),

messageCounts: {

total: 10,

user: 5,

} as unknown as UsageSessionEntry;

const result = buildPeakErrorHours([session], "utc");

// Should still produce results via the proportional allocation fallback

expect(result.length).toBeGreaterThan(0);

// All errors (3) should be distributed proportionally

const totalErrors = result.reduce((sum, r) => {

const match = r.sub.match(/(\d+) errors/);

return sum + (match ? Number.parseInt(match[1], 10) : 0);

}, 0);

expect(totalErrors).toBe(3);

expect(result.map(({ value, sub }) => ({ value, sub }))).toStrictEqual([

{ value: "30.00%", sub: "3 errors · 10 msgs" },

]);

});

});