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openspec/changes/complete-rng-unification/specs/testing/spec.md

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+# Capability Spec Delta: testing (testing)
+
+**Package**: `@suaveplan/testing`
+**Status**: PROPOSED
+
+> Every requirement below carries a `**Verified by:**` line at authoring time. No exceptions.
+
+## MODIFIED Requirements
+
+### Requirement: Rng surface re-exports the canonical type
+
+`@suaveplan/testing` SHALL re-export the canonical `Rng` interface from `@suaveplan/types` rather than declaring a local `interface Rng`. The re-export lives at `src/context/context.ts` and is named `Rng`, preserving the existing consumer import path (`import type { Rng } from "@suaveplan/testing"`) for one release cycle. The local `cryptoRng` and `seededRng(seed)` factories SHALL continue to satisfy the canonical type — they provide the required `nextUint32` / `nextFloat` members and omit the optional `nextBytes` / `nextIntInRange` members. The package SHALL add `@suaveplan/types` to `dependencies` as `workspace:^`; this is the sole `@suaveplan/*` runtime dependency permitted for testing-infrastructure packages under CLAUDE.md rule 8, and is allowed because `@suaveplan/types` is types-only and emits zero runtime (verified by the byte-size guard).
+
+**Verified by:** `packages/testing/testing/src/context/context.ts` (re-export line `export type { Rng } from "@suaveplan/types"`) AND `packages/testing/testing/src/context/context.test.ts::"cryptoRng satisfies canonical Rng"` AND `packages/testing/testing/src/context/context.test.ts::"seededRng satisfies canonical Rng"` AND `packages/testing/testing/package.json` `dependencies` contains `"@suaveplan/types": "workspace:^"` AND `bunx turbo test --filter=...@suaveplan/testing` (foundation dependent sweep).
+
+#### Scenario: local Rng re-export forwards canonical
+
+- **WHEN** a consumer writes `import type { Rng } from "@suaveplan/testing"`
+- **THEN** the imported type is structurally identical to `import type { Rng } from "@suaveplan/types"`
+
+#### Scenario: cryptoRng satisfies canonical
+
+- **WHEN** `const r: import("@suaveplan/types").Rng = cryptoRng`
+- **THEN** `tsc` accepts (cryptoRng provides nextUint32 + nextFloat; optional members omitted)
+
+#### Scenario: seededRng satisfies canonical
+
+- **WHEN** `const r: import("@suaveplan/types").Rng = seededRng(42)`
+- **THEN** `tsc` accepts AND `r.nextUint32()` is deterministic given seed 42
+
+#### Scenario: byte-size guard remains green
+
+- **WHEN** the testing-infra byte-size guard runs after `@suaveplan/types` is added as a dependency
+- **THEN** the guard exits zero (because `@suaveplan/types` emits zero runtime bytes — it is a types-only package)