Per-cell CellStyle rendering: bgColor, textColor, font, alignment, borders

[witqq]

Summary

All 15 CellStyle properties are defined in the type system and StylePool is fully implemented, but no render layer reads cellData.style — zero per-cell styling is rendered.

Current State

• BackgroundLayer fills entire canvas with single theme.colors.background
• CellTextLayer uses global theme.colors.cellText and theme.fonts.cell for all cells
• GridLinesLayer draws uniform grid lines from theme
• CellStyle.textAlign is ignored — alignment comes from CellTypeRenderer.align (per column type)
• CellStyle.textWrap is ignored — wrapping comes from ColumnDef.wrapText (per column)
• CellStyle.verticalAlign is ignored — always middle
• CellStyle.indent is not read anywhere

Required Changes

Phase 1: Core styling (bgColor, textColor, font)

• New CellBackgroundLayer (or extend existing) — iterate visible cells, fill per-cell bgColor
• CellTextLayer — read cellData.style for textColor, fontFamily, fontSize, fontWeight, fontStyle
• Font string construction: per-cell override > theme default

Phase 2: Alignment & layout

• textAlign — per-cell override of CellTypeRenderer.align
• verticalAlign — support top/middle/bottom
• textWrap — per-cell override of ColumnDef.wrapText
• indent — add left padding

Phase 3: Per-cell borders

• GridLinesLayer — per-cell border color, width, style (solid/dashed/dotted)
• Requires careful handling of shared borders between adjacent cells

Motivation

Real consumers (e.g., planeta-worktree2) are forced to create custom RenderLayer overlays that paint white over engine output and re-render because the engine ignores per-cell styles. This is the correct extension point but should be unnecessary for basic styling.

Files to modify

• packages/core/src/renderer/layers/cell-text-layer.ts
• packages/core/src/renderer/layers/background-layer.ts (or new CellBackgroundLayer)
• packages/core/src/renderer/layers/grid-lines-layer.ts (Phase 3)
• packages/core/src/renderer/render-context.ts (may need StylePool in context)