v5.9.9

[5.9.9] - 2026-08-05

Revert: v5.9.8's day_night phase change broke the fully-closed look

User-caught regression, tested live the same day: after v5.9.8, a day_night blind at fully
closed (even with top_offset: 0, i.e. no correction at all) rendered visibly "a bit open"
instead of solid. Root cause: the old formula's pct>=1 → offset = one half-period special case
wasn't an arbitrary discontinuity as v5.9.8 assumed — it was the load-bearing anchor that
keeps the two striped background layers in anti-phase at fully closed, which is what makes the
blind render fully opaque (no see-through gaps) when drawn. v5.9.8's "continuous, no special-case"
replacement reached offset 0 at fully closed instead — aligning the two layers instead of
anti-phasing them, letting the gaps show through everywhere, including at 100% coverage.

Reverted the render formula to its exact pre-5.9.8 behavior. Removed the rocDayNightOffset
helper and its tests (smoke + render) added in 5.9.8, since they encoded the incorrect model.

Structural finding (kept for any future attempt — see ROADMAP.md 🅿️ day_night blind model)

While reverting, traced the two-layer compositing precisely: one gradient layer is permanently
fixed at background-position 0, the other scrolls with pct. Because the fixed layer's pattern
always starts solid at position 0, and the fill area always starts at row 0 (top-anchored),
the very first visible row of any day_night fill is unconditionally opaque, at any pct, at any
phase — the fixed layer guarantees it whenever the scrolling layer happens to be transparent
there. This means a residual sliver that is purely transparent (as opposed to "mostly transparent
with an always-present opaque cap row") is not achievable via phase-tuning alone with the current
two-fixed/one-scrolling rendering approach — it would need a structurally different mechanism. This
is exactly the kind of finding the ROADMAP's parked note asks for before any further day_night
redesign is attempted; documented there for whoever (likely the same author) picks this up next.
top_offset continues to correctly control coverage amount for day_night blinds (that part
of v5.9.7 is unaffected and still correct) — it just doesn't (and currently can't cleanly) also
control the striped pattern's exact phase.

Testing

Full smoke + render suites green (0 FAIL) after the revert.