deepseek-harness/packages/util/brand

dsh-brand

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The Branded<B> nominal-typing primitive — a tiny, type-only package (no runtime code, no harness-package dependency) shared by every package that owns a cross-boundary id.

What Branded is

A brand makes structurally-identical strings non-interchangeable at the type level: a SessionId cannot be passed where a CallId is expected, even though both are plain strings at runtime.

import type { Branded } from '@deepseek-ai/dsh-brand'

export type SessionId = Branded<'SessionId'>

/** Brand a string as a SessionId (a plain cast — zero runtime cost). */
export function SessionId(id: string): SessionId {
  return id as SessionId
}

Construction goes through the per-id factory in the owning package. Comparison, logging, JSON serialization, and the wire format behave as for an ordinary string; the brand is erased at compile time.

Policy: brand ids that cross package boundaries

A package brands the ids it owns — CallId in dsh-llm, the shared agent/session SessionId in dsh-session, and TaskId in dsh-tasks. Brand cross-package ids that could plausibly be confused; not every string needs one.

This package owns only the primitive. Keeping it dependency-free lets dsh-tasks, for example, brand TaskId without importing an unrelated capability package merely to reach Branded.