Rail cells: one thin selection ring; working blink pulses the fill

[theogravity]

Two operator rulings on the sidebar's cell view, dated 2026-09-27.

Selection. Every open pane's cell wears ONE soft ring-1 ring-foreground/70, the focused one included. The ring-2 focus bump arrived with #260 the same day and read too heavy at cell size; at one width the two levels stop being tellable apart, so there is one level. Rows keep their two-signal shape (set = accent fill, focus adds the ring) — untouched.

Working state. The solid-green + dark-knockout beat is retired: the cell now pulses the bg-success/50 fill behind a constant white initial. On the transparent half an un-ringed cell keeps a static --border frame (a letter floating on bare rail read broken; where the selection ring is, the ring IS the frame). The white letter on the rail is what let the tile vanish the way the dot's does — images #10/#11/#14 were all symptoms of stranding a DARK letter, which the now-deleted blink-alt complement existed to pair. DOT_CLASS.active still drives the dot itself.

Tests: the cell-grid blink test and the two rail selection tests were rewritten to pin the new shapes (bare-token assertions, ring-2 asserted absent, one letter not two, frame on the anchor only when un-ringed). sidebar.md carries the updated account; a changeset for @internal/server ships it.

Verified: full verify-types / lint:check / test trio green, plus focused runs after the final border change (28 cell tests, 20 rail tests, tsc, biome, lint:design).

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