Premium Analytics: fix the sub-day previous-period comparison range

[retrofox]

Proposed changes

The sub-day branch of getComparisonRangeFromPreset() mirrors a rolling window by shifting both ends by to - from. The ends are inclusive, so that span is one millisecond short of the window's real duration, and the shifted to lands exactly on the reference's from: the first instant of the primary window instead of the last instant before it.

At day granularity the stray millisecond never crosses a day boundary, so nothing was visible. At hourly granularity (#51166) it pulls the whole comparison series one bucket late: its last bucket is the primary's first, and the previous-period tooltip names the next hour. Root-cause context in this #51166 comment.

The fix shifts previous-period by the inclusive duration (windowMs + 1). The previous-month and previous-year branches already preserve the inclusive shape through their calendar shift, so they stay untouched.

The sub-day tests now use inclusive ends, the shape every preset actually produces (endOfHour, endOfDay); the old exact-instant reference was asserting the buggy boundary. A new case pins the last-24-hours shape, and another the adjacency invariant: the previous window ends immediately before the reference begins.

Related product discussion/links

• Premium Analytics: Traffic chart follows the global interval control, including hourly #51166 (comment): where the symptom was reported (previous-period tooltip on Last 24 hours)
• WOOA7S-1902: the hourly Traffic work this unblocks

Does this pull request change what data or activity we track or use?

No.

Testing instructions

pnpm --dir projects/packages/premium-analytics run test

get-comparison-range.test.ts pins the mirror. On trunk alone there is no visible change: at day granularity both boundaries resolve to the same calendar days. With #51166 checked out on top, pick Last 24 hours with comparison on and hover the Traffic chart: the previous-period row names the same hour as the tick under it, one day back.

[github-actions]

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Code Coverage Summary

Cannot generate coverage summary while tests are failing. 🤐

Please fix the tests, or re-run the Code coverage job if it was something being flaky.

Full summary · PHP report · JS report

[chihsuan]

Thanks @retrofox LGTM and tested well 🚀