Expose vertical writing through the API, MCP, and the agent skill

[dani-polani]

Follow-up to #18, which shipped column layout in the editor only. This makes it reachable programmatically and from an AI assistant.

What's added

Two fields, both following the existing rtl precedent:

• settings.axis — "rows" (default) or "columns"
• lines[].orientation — "upright" (default), "vertical", or "sideways"

The API only encodes state into a URL, so none of the layout work from #18 is involved here.

curl -X POST /api/align -H "Content-Type: application/json" -d '{
  "lines": [
    { "text": "The cat ate the fish", "sizePx": 26 },
    { "text": "猫 が 魚 を 食べた", "orientation": "vertical", "font": "Noto Serif JP", "sizePx": 34 }
  ],
  "alignments": [[0,0,1,0],[0,1,1,0],[0,3,1,2],[0,4,1,2],[0,2,1,4]],
  "settings": { "axis": "columns" }
}'

One trap worth knowing about

axis is spelled layoutAxis internally, and settings were merged with a spread. Left in the spread it would have landed as a stray key that the compact encoder silently drops: the field would have validated, the request would have succeeded, and the diagram would have come back horizontal. It is pulled out and mapped by hand, with a test asserting the decoded state rather than just the accepted input.

Unknown values are rejected with a named error instead of being normalized, matching palette and lineStyle.

Docs

pairs[].upper / lower mean earlier and later in the stack. That is above/below in rows but left/right in columns, and the names now say so on the /api page. The MCP tool description said links must be "vertically adjacent"; corrected, and both surfaces now state that Japanese and Chinese are not segmented for you. OpenAPI, the /api page, and the agent skill get a worked tategaki example.

Verification

196 tests green (7 added, covering both fields, the decoded state, defaults, and rejection of bad values). Driven end to end: POST to the running API, then the returned URL opened in Chromium — columns present, Japanese stacked, English upright beside it.

Found along the way, not fixed here

/api/og renders "NO GLYPH" boxes for any non-Latin script. og-fonts.ts bundles only Inter, loadSystemFonts is off, and the deploy image (node:22-bookworm-slim) has no fonts. This predates vertical writing: the horizontal Japanese example breaks the same way. It affects social cards for every non-Latin gallery page and the inline PNG the MCP tool returns. Left alone deliberately, since the fix is a build-weight tradeoff; tracked separately.

🤖 Generated with Claude Code