render: single-value formatters as a headless @malloydata/render/format entry

[lloydtabb]

Why

A value's display format (# currency, # percent, # duration, # number) could only be applied by mounting the renderer:

• the formatters take a data-tree Field, and
• the package's one entry loads Solid, Vega and the DOM.

Anything else that wants a value to read the way a rendered table shows it has had to reimplement the formats and drift from them. That includes a server writing "$521k" into a summary, a dashboard drawing its own KPI card, and an LLM reporting a number. Concretely, Malloyyo now hands each result column's declared format to its MCP clients (malloydata/malloyyo#204) and wants a format(path, value) for custom dashboards that matches the renderer exactly.

What

src/format/: the formatters, with no Field.

• resolveCellFormat(tag, {isTime}) → CellFormatConfig. This is the same plain-data config resolveCellFormatTags already produced, and it survives JSON.stringify.
• formatNumber(value, config) handles numbers, plus digit strings for exact bigints.
• formatDateTime(value, config, {timeframe, isDate, timezone}).
• formatDuration, formatScaledNumber, renderTimeString, NULL_SYMBOL.

The renderer uses the same code. resolveCellFormatTags and the render*Field helpers are now thin wrappers that add only the Field lookups (its resolved config and its query timezone). Rendered output is unchanged. util.ts re-exports everything that moved, so existing imports keep working.

A new export, @malloydata/render/format. It's built separately by vite.config.format.mts into dist/format/index.{mjs,cjs}, with types from the main build's dist/module/format/.

• Self-contained like the main build (external: []). Leaving dependencies external breaks Node ESM: ssf is CommonJS-only, and lodash/startCase is an extensionless subpath.
• About 113 KB as CJS (36 KB gzipped), against 3.5 MB for the UMD renderer.
• Loads in plain Node with no DOM stub, under both import and require. Checked through the package exports.

CONTEXT.md documents the second entry and the rule that keeps it headless: no data_tree, Solid, Vega or DOM imports in src/format/.

Tests

• New src/format/cell-format.spec.ts covers resolution (currency shorthand, percent, duration, # number as a date pattern only on time fields, default, JSON round-trip) and formatting (currency, percent, number shorthands and ssf patterns, duration, bigint strings, null, date patterns, timeframes). The malloy-render jest project has no DOM setup, so this also shows the module doesn't need one.
• malloy-render: 228/228 passed (the repo's jest config pins TZ=America/Los_Angeles). malloy-render-test (DOM renderer): 76 passed, 28 skipped. Consumer canary passes. tsc -p tsconfig.type-check.json, eslint and prettier are clean, and the full monorepo npm run build succeeds.

Date patterns now read the query's zone, not the host's (behaviour fix)

Before this PR, # number="mmm yyyy" handed a Date to ssf, which reads the host's local fields. So 1 Sep 2026 00:00 UTC rendered "Aug 2026" in any browser west of UTC, and a server and a browser could disagree. formatDateTime now formats the value's wall clock as a spreadsheet serial date, which carries no zone:

• a timestamp reads in the query's time zone (the renderer passes the field's effective query_timezone, as it already did for the default path), otherwise UTC;
• a date reads as its UTC calendar day.

This is the one change to rendered output: date-pattern fields on hosts that aren't in the value's zone, where the output was wrong. The spec covers the UTC midnight-on-the-1st case, a query time zone and a date. Note that jest.config.ts pins TZ=America/Los_Angeles, so the repo's suite only ever runs west of UTC. I also ran the spec with that line removed under UTC, America/Los_Angeles, Asia/Tokyo and Asia/Kolkata, and it passes in all four.

Differential check, old vs new. Using a throwaway harness (not committed), I rendered 7,824 cells through the renderer's own pipeline (RenderFieldMetadata → getDataTree → renderCellValue) on both main and this branch, with the host in the same four zones:

• 28 number/currency/percent/duration formats × 13 values, plus bigints;
• 12 date patterns plus no pattern, × every date and timestamp timeframe;
• 5 query time zones, plus a nest with its own timezone:.

The results:

• Every number, bigint and duration cell is identical, in every zone.
• Every cell that differs uses a date pattern.
• The new output is the same in all four host zones. On main, 5,070 of the 7,824 cells changed with the host's zone.
• The harness also found a crash that exists on main: # currency=gbp… and # currency=pound throw unrecognized character £ in ssf. It's unchanged by this PR and worth its own fix.

Review follow-ups (second commit)

• typesVersions maps format to its .d.ts. Checked: moduleResolution: node10 fails with TS2307 without it and resolves with it; bundler and node16 resolve either way.
• resolveCellFormat returns a fresh default config instead of one shared object stored on every untagged field.
• The invalid-date-pattern warning names the field again.
• The legacy renderer's duration text (html/duration.ts) reuses formatDuration, which now takes the per-part # number pattern the legacy code applied, so only one copy of the duration logic remains.
• The unused util.getText wrapper is removed.
• Not changed: the ES build of ./format is about 258 KB unminified, against 113 KB for CJS. Vite's library mode won't strip whitespace from ES output, even with build.minify.

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