feat(roadmap): rule the axis symmetrically around today - #917

Summary

The graduated roadmap axis now rules time the same way in both directions from today. Last week, this week and next week are shown a column a day. Before and after those come three weeks, then months for at least a quarter, then quarters. Before this change only this week was in days, and history coarsened differently from the horizon (four weeks, then months, never quarters).

Changes

• RoadmapWindow.Graduated builds symmetric tiers:
  • GraduatedDayWeeks = 1: the day columns run from the start of last week to the end of next week.
  • GraduatedWeeks is now 3 week columns on each side (it was 4 in history and 3 ahead).
  • The past monthly tier starts on a quarter boundary, at least a quarter before the weeks, and quarter columns come before it.
  • History's months and quarters still reach only as far back as the earliest thing drawn. The days and weeks are always there.
  • The first day of each day-week carries its week number. The first week after the days names its month, because day columns never name one.
• RoadmapTimeline.FillFrom: a graduated chart now opens on last week, so the days before today are in view.
• .devbook/domain/roadmap/features.md: Reading the near term closely and Looking back at finished plans now describe the new axis.

Reviewer note: the forward months now start a week later. The partial month next to the weeks is narrower as a result (on 25 Sep it is 6 days of October instead of 13), so its head label may drop below the minimum width to show.

Testing

• RoadmapGraduatedAxisTests updated to the new layout, plus a new test for quarter and month history (LongAgo_IsRuledInQuarters_ThenWholeMonthsFromAQuarterStart).
• dotnet build Backlog.sln: 0 warnings, 0 errors.
• dotnet build Backlog.WithoutAppHeads.slnf -c Release -warnaserror: 0 warnings, 0 errors.
• dotnet test reported "Zero tests ran", so I ran every test project's executable directly: all 28 assemblies passed with 0 failures.
• node .devbook/_tools/devbook-meta/build.mjs --check and tools/devbook/check-metadata.mjs: 0 blocking.
• Desktop web harness through Aspire, on today's date (Thu 1 Oct 2026). The axis reads W36–W38 (3 weeks), then Mon 21 Sep–Sun 11 Oct (21 days), then W42–W44 (3 weeks), then Nov 2026–Mar 2027 (months), then Q2–Q3 2027. It opens scrolled to W39. The harness logged no errors.

Related

No issue: this was an ad-hoc request from a session.

Checklist

• Scope is focused and excludes unrelated changes
• Documentation or instruction files were updated when governance or behavior changed
• Running Aspire instances for this checkout were stopped before PR creation (build\stop-aspire-before-pr.ps1)
• Follow-up work is captured when the implementation is intentionally partial
• Issues this PR closes are linked with a closing keyword, or there are none

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