[feat] kit: reusable build-your-own core + examples (STAR-45)

[vt128]

What & why

starcli is the standard, fully-loaded build. STAR-45 introduces a build-your-own track: a few-line Go shell that embeds your Starlark scripts and wires only the modules you need. To keep the project consistent, the CLI's runtime construction is factored into a small reusable core — github.com/1set/starcli/kit — that both the turnkey CLI and a user's own shell go through, so they behave identically.

Go is the shell, Starlark is the app. main.go stays a few lines; logic lives in //go:embed'd .star files.

kit

Turns an embedded script + chosen modules + runtime knobs into a ready-to-run starbox. Depends only on starbox + starlet (never on any starpkg module), so a build-your-own shell pulls in only what it actually wires. Three composable wiring styles:

Option	Resolves as	For
WithModules("json","math")	starlet builtins	the stdlib
WithLoader("qrcode", loader)	an explicit loader you import	a specific starpkg/custom module
WithDynamicLoader(fn)	a registry on demand	exposing many modules (how starcli itself wires every starpkg module)

Unity (the CLI reuses it)

BuildBox is rewritten to translate its options into kit options and delegate construction to kit.Box(). CLI-specific concerns (capability gating, scenario printer, file logging) stay in the cli layer as a thin wrapper. The existing e2e/web/cli suites pass unchanged — the refactor is behaviour-preserving.

Examples

examples/ is a separate Go module (minimal deps, out of the coverage gate):

• hello — the smallest shell (embed + one call)
• qrcard — wiring a single starpkg module (qrcode); its whole dep tree is starbox + qrcode
• a build-your-own quickstart README

A non-gating CI job builds the examples module.

Verification

• go test -race -count=2 ./... green (incl. e2e/web safety net)
• kit coverage 97.5%; total 76.3% (floor 65)
• gofmt/go vet clean; examples build + vet + run locally

Refs STAR-45.

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