Script-first MVP

The rule. When a new capability's contract is uncertain, build it first as a local script (bash and the standard Unix toolbox) operating on real data, outside the Go core. The script's job is to discover the contract — the on-disk shapes, the failure modes, the verbs worth having. The Go core absorbs the proven contract, never the script; the script then serves as reference implementation and dogfood until the native verb is wired.

Why. The single-binary boundary makes premature absorption expensive: a wrong contract baked into internal/core costs a schema migration and a release, while a script iterates at conversation speed against real data. What stabilises under real use is the on-disk contract — folders, JSON shapes, exit codes — which is exactly the part a Go port keeps verbatim. Learning happens where iteration is cheap; permanence happens where the contract is proven.

Bounds.

• A script MVP lives in the personal/local tier (a user-home bin/, a repo's scripts/), never ships as product behaviour, and is never the thing "wired or it isn't done" is claimed against — that bar applies to the Go absorption.
• A plugin surface may front a script MVP early (one surface across the later swap), but it must stop gracefully where the script is absent.

Live instance. The sources-corpus tooling (user-tier registrar, ingest wrapper, banlist projection, cite guard) proved the per-source-folder + CSL-JSON + append-only-ledger contract as bash before any Go verb exists; its absorption into the core is iss-27, converging with the itd-36 provenance substrate. The consult and ingest skills that fronted it became command pages and then retired into /abcd:library, which fronts it per the bounds above.

Promotion. This principle is the capability-specific instance of the MVP → tool edge of the ladder in this directory's README: the script is the enabling MVP, the Go-core absorption the tool. No enforcement hook exists; per the promotion path in this directory's README, this file becomes a discipline-kind intent the moment one does.