[dangreen]

Why

Some messages need code to decide what they render: a template that applies only when every part is present, values changed before they are filled in, a locale-aware change of the result. Today that logic lives in helpers at the call sites, like a getGardenPlace(t, garden) that renders '{city}, {country}' only when both parts are present and the part alone otherwise. Every call site has to remember the helper, and the message type is declared again by hand next to it.

wrap moves that logic into the scheme, so the message renders the same everywhere:

const [$t] = messages('garden', {
  location: wrap(params({
    city: text(),
    country: text()
  }), (place, message) => (place.city && place.country ? message(place) : place.city || place.country))
})

$t().location(garden.location)

What

• wrap(format, fn) works with any format. A value, like the result of text(), reaches fn as is with the active locale: (message, locale). A message function, like one of params, plural or match, reaches it as is after the values of its call read from signals and accessors: (values, message, locale). fn calls the message with the values it chooses, changed ones included, or returns something else instead.
• The wrapped message renders only when fn calls it: a guard that skips it neither fills placeholders nor warns about a parameter without a value, and a value returned instead is used as is.
• One signature with the conditional WrapArgs<R> and Wrapped<R, O> types instead of overloads: with overloads, TypeScript infers unknown for the message of an inline call with arguments, like datetime({ dateStyle: 'medium' }).
• A format() message is wrapped from the inside, format(wrap(datetime(), fn)), as with capitalize. Wrapped from the outside, messages() would take it for a translated message and warn that it is missing, since it tells the two apart by the arity of the format.
• Docs: a "Wrapping Messages" section on the intl API page, a line in the format list of Core Concepts, a convention in the nano-kit-intl skill and its regenerated DOCS.md.

Size

Entry	Before	After	Limit
@nano_kit/intl All publics (Gzip)	2234 B	2303 B	2.25 → 2.35 kB
@nano_kit/intl All publics (Brotli)	2074 B	2140 B	2.1 → 2.15 kB

Minimal set and Basic set are unchanged. Importing wrap next to { intl, text, params } adds 78 B gzip.

Verification

oxlint, tsc --noEmit and vitest are clean in @nano_kit/intl (144 tests, 11 of them for wrap) and size-limit passes. The pre-push pnpm test passes across the monorepo, pnpm skills:docs --check passes and the website builds. Every example of the new docs section was compiled and run against the package.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 83.66%. Comparing base (c9266af) to head (661f1e0).

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #311      +/-   ##
==========================================
+ Coverage   83.62%   83.66%   +0.03%     
==========================================
  Files         228      229       +1     
  Lines        4849     4860      +11     
  Branches     1074     1075       +1     
==========================================
+ Hits         4055     4066      +11     
  Misses        553      553              
  Partials      241      241              

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