The cubek-ts subset

Run `cubek skill`, read all of it and follow it exactly (no CLI: download https://cubek.dev/SKILL.md verbatim with curl; don't summarize it); when you write any TypeScript for this project, follow its "The cubek-ts subset" section.
Run `cubek check` after every edit until it is clean.

cubek check rejects (with the fix) server npm, node:*, process, Buffer, any, .then (await, Promise.all), timers, obj[key] on fixed fields (Record<"a" | "b", T> too; arr[i], Record<string, T> fine), for...in, delete, user generics, Intl, local-time Date, URL, Object.groupBy, reading unknown... Untrusted data (JSON.parse, caught errors) is checked, never cast as T: input.safeParse(JSON.parse(text)) or narrow (Array.isArray(v), "k" in v, e instanceof Error). Not taught by an error:

Not in cubek-ts	Use
class E extends Error	return { ok: false, error }
getUTCSeconds	slice toISOString()
className, page onClick, dangerouslySetInnerHTML	class, a mount point or form, raw(...)

Annotate the return types of named functions.