# api-host-testing-kit — Populate Stage-5 ./testing subpath

## Why

`@suaveplan/api-host/testing` has shipped a `STAGE_2_RESERVED` sentinel since Stage 2. Stage 5 in-memory adapters (`api-router-in-memory`, `api-auth-static-principal` / `api-auth-anonymous`, `api-db-sqlite-memory`, `api-events-in-memory`, `api-ws-broker-in-memory`, `api-tenant-provider-memory`, `api-secrets-env`) have all shipped, but no host-side composition surface drives them together. Plugin authors writing integration tests have to hand-wire every adapter slot at the call site — the same boilerplate observed in `e2e/foundation-stack/src/server.ts`. The keystone for the Stage-5 testing kit is a `createTestHost(config?)` factory that composes every default in one line.

## What changes

- Replace `STAGE_2_RESERVED` placeholder with the full `createTestHost(config?)` factory under `src/testing/create-test-host/`.
- Surface flips: the sentinel constant changes from `true` to `false` (back-compat preserved — consumers that branched on `=== true` still compile; the populated helpers ship alongside).
- New types: `TestHostConfig`, `TestHostSeed`, `TestHostAdapters`, `TestHost`, `FixturePluginInstall`, `FixtureRouteRegistration`.
- `TestHost` extends `Host` with `installFixturePlugin`, `fetchAs`, `waitForEvent`, `dispose`.
- Default adapter resolution per-slot, override-beats-default semantics.
- `seed.principal` / `seed.tenants` / `seed.secrets` populate the default adapter inputs.
- Companion smoke at `e2e/foundation-stack-test-host/` boots a Bun.serve over `createTestHost(...)` and drives every wired slot through real HTTP with Playwright.
- `suaveplan.conformanceSkip` for api-lifecycle / api-loader / api-manifest / api-secrets retained (api-host is the consumer/driver, not the implementer); the gap is documented in README + this proposal.

## Impact

- Affected specs: `api-host`
- Affected code: `packages/api-stack/api/api-host/src/testing/*`, `packages/api-stack/api/api-host/package.json` (peerDependenciesMeta + new devDependencies for the in-memory adapters), `e2e/foundation-stack-test-host/*` (new workspace).
- Affected downstream: every package previously branching on `STAGE_2_RESERVED === true` can now opt into the populated helper; no breaking change.