UAN-002 house TypeScript style review

Reviewed 2026-10-10 against the owner's TypeScript house guide (version 1.0.0, updated 2026-09-23). The scope was all owned TypeScript in src/ (about 6,900 lines). The examples contain no .ts/.tsx sources: their callbacks are .mjs with JSDoc types, which this TypeScript-only guide does not cover. The emitted Astro export default defineConfig(...) template in src/init.ts is third-party framework output and stays as Astro requires.

Deviations found and changed

Guide rule	Before	After
Maximum practical compiler strictness	`noImplicitReturns` missing from the baseline	Added to `tsconfig.json`; no errors resulted
Avoid lint rules that rewrite intentional `let`	Biome `recommended` enabled `style/useConst`	`style/useConst` is off. `complexity/useLiteralKeys` is also off, because it contradicts `noPropertyAccessFromIndexSignature` bracket access. The rest of `recommended` remains
`const` means immutable; `let` means mutable	Collections were held in `const` bindings and then pushed to or set	Mutated bindings use `let`. Never-mutated ones keep `const` with `readonly T[]`, `ReadonlySet`, `ReadonlyMap` or `Readonly<Record<…>>`
No non-null assertions	10 postfix `!` in `src/init.ts`	Replaced with visible `requireAt`/`requireValue` helpers. Each value was already established, so behavior is unchanged
Shared `assertNever`	Owned-union switches over execution failures and harness events had no compile-time exhaustiveness	`src/core/assert-never.ts` (internal) closes the switches in `http.ts`, `mcp.ts` and `browser.ts`. `harness.ts` uses a local `never` guard that keeps its `HarnessError` for untrusted input
Explicit types by default; explicit callback types	Locals, callbacks, default-valued parameters and some helpers relied on inference	About 460 locals were annotated with the types tsc inferred, plus callback parameters and returns, default-valued parameters and class fields. Async functions declare `Promise<T>`, and `runTurn` declares its `AsyncGenerator` type. A few internal aliases name repeated shapes
`interface` for implementation contracts	`HarnessMcpBridge`, `BrowserCapabilityAdapter`, `WebMcpModelContext`, `NextBrowserBootstrap` and `McpAppRegistration` were object `type`s	Now interfaces. This is structural and source-compatible for consumers

The emitted declaration files were compared with a build of the previous source. Exported names, signatures and value types are unchanged apart from equivalent spellings.

Deliberate exceptions

PACKAGE_VERSION stays unannotated because scripts/check-package-version.mjs matches that exact line.
DOCTOR_REPORT_SCHEMA_VERSION and DOCTOR_REPORT_JSON_SCHEMA keep their inferred types. Annotating them would change exported literal types.
as const/satisfies precision sites stay as they are, which the guide allows.
HarnessEvent is a released public union discriminated by type rather than kind. Renaming it would break the 0.1.1 API, so it is left for a future major version.
Remaining void promise.catch(handler) calls use handlers that cannot throw, which the guide accepts.

Verification

npm run format:check, npm run lint, npm run typecheck (all three tsconfig projects), npm run build:browser-proof and the full unit suite pass. That includes 124 non-harness tests and 6/6 Codex harness tests. The full npm run check and the isolated-export check repeat these on the committed source.