fix(aws): daily coverage call sets Granularity with GroupBy, which Cost Explorer rejects

[cristim]

Summary

The daily-sparkline coverage call sets both Granularity and GroupBy on GetReservationCoverage, which the API documents as mutually exclusive. Every real call returns a ValidationException, which the caller logs at warning level and swallows, so the per-row usage-history feature is dead in production while collection looks healthy. Mock-backed tests stay green because none of them assert Granularity on this input.

Location

providers/aws/recommendations/usage_history.go:85 at 3c0f8ac94048a2c36fce5ccddee54e6c4849a5cd

Failure scenario

The GetReservationCoverage SDK operation doc states "If GroupBy is set, Granularity can't be set." fetchDailyCoverage sets both, so every real call returns a ValidationException. AttachDailyUsageHistory logs the error at WARN and continues, so the entire per-row usage-history feature is dead in production while the collection looks healthy. No test asserts Granularity on this input (the three GranularityDaily assertions in the package are in ondemand_series_test.go and sp_coverage_test.go, whose operations do accept it), which is why mock-backed tests stay green. The sibling path in coverage.go correctly omits Granularity when it sets GroupBy.

Evidence

input := &costexplorer.GetReservationCoverageInput{
    TimePeriod:  &types.DateInterval{...},
    Granularity: types.GranularityDaily,
    GroupBy: []types.GroupDefinition{
        {Type: types.GroupDefinitionTypeDimension, Key: aws.String(string(types.DimensionInstanceType))},
    },
    Filter:  dailyUsageFilter(serviceFilter, region),
    Metrics: []string{"Hour"},
}

Suggested fix

Drop the Granularity field (the response is already per-day when the time period is daily-resolvable), and assert its absence in the test so the pair cannot be reintroduced.

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Found by the 2026-09-02 codebase audit, finding A07-010, reported by one reviewer and independently confirmed by a second. Full report: docs/audits/codebase-audit-2026-09-02.md.