27 lines
1.7 KiB
Markdown
27 lines
1.7 KiB
Markdown
# 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.
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## What `Branded` is
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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 `string`s at runtime.
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```ts
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import type { Branded } from '@deepseek-ai/dsh-brand'
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export type SessionId = Branded<'SessionId'>
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/** Brand a string as a SessionId (a plain cast — zero runtime cost). */
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export function SessionId(id: string): SessionId {
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return id as SessionId
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}
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```
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Construction goes through the per-id factory in the OWNING package (a plain cast inside — zero runtime cost). Comparison, logging, JSON serialization, and the wire format all behave exactly as for an ordinary string; the brand is erased at compile time.
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## Policy: brand ids that cross package boundaries
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A package brands the ids it OWNS — `CallId` in `dsh-llm` (tool-call correlation), the shared agent/session `SessionId` in `dsh-session`, and `BashTaskId`/`OwnerToken` in `dsh-bash`. Branding is for ids that cross package boundaries and could plausibly be confused; **not every string needs a brand.**
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This package owns ONLY the primitive — no concrete id, no runtime code beyond the (erased) type. Keeping the primitive dependency-free is the point: a capability package can brand its ids without depending on an unrelated package. `dsh-bash`, for example, brands `BashTaskId`/`OwnerToken` by depending on `dsh-brand` alone — it never pulls in `dsh-llm` (or `dsh-session`) just to reach `Branded`.
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