docs(plan-9): doc-pass slice 1 — CLAUDE.md, core-shared AGENTS, architecture, plan-8 annotations

First slice of the combined Plan 8 + Plan 9 doc-update pass:
- CLAUDE.md Key Conventions: append schema-in-use-case, presenter,
  controller unknown input, feature-scoped tRPC error mapping, public
  surface split (./ui)
- packages/core-shared/AGENTS.md: document defineErrorMiddleware export
  + t re-export from trpc/init
- docs/superpowers/plans/2026-05-05-plan-8-*.md and matching spec:
  one-line note that some controller/router patterns shifted in Plan 9;
  link to the Plan 9 refactor log
- docs/architecture/overview.md: data-flow box now shows xProcedure +
  xInputSchema + xOutputSchema.parse + presenter + middleware lanes;
  three explanatory paragraphs added (schemas, presenter, error mapping)
- docs/architecture/dependency-flow.md: app-side ./ui subpath note,
  allowed/disallowed examples updated for Plan 9 paths

Remaining doc-pass items (root AGENTS.md, per-feature AGENTS.md ×5,
core-testing AGENTS.md, adding-a-feature.md, tdd-workflow.md,
testing-strategy.md, vertical-feature-spec.md) follow in subsequent
commits — to be dispatched in parallel.

CLAUDE.md

@@ -43,6 +43,10 @@ Turborepo + pnpm monorepo organized by vertical features. Each feature (`auth`,
 - **Factory-function use cases & controllers** — Every use case and controller is `(deps) => async (input) => result`; each exports `export type I*UseCase = ReturnType<typeof xUseCase>` (and the analogous `I*Controller`); one controller per use case (no multi-method controllers)
 - **DI uses `.toDynamicValue()` for factories** — `bind<IXUseCase>(SYMBOL).toDynamicValue((ctx) => xUseCase(ctx.container.get(...)))`; mocks remain the default binding
 - **Tests inject mocks directly** — Construct `MockXRepository` and pass into the factory: `signInUseCase(mockUsers, mockAuth)(input)`. No container rebinding in unit tests
+- **Schemas in the use-case file** — Every use case exports `xInputSchema` (a `z.ZodObject` with `.strict()`; `z.object({}).strict()` for void inputs) and, for non-void use cases, `xOutputSchema`. Types: `XInput = z.infer<typeof xInputSchema>` and `XOutput`. Use case body ends with `xOutputSchema.parse(result)` before returning (runtime guarantee against malformed repository data)
+- **Controllers receive `unknown` + presenter** — Controllers `safeParse(xInputSchema)` from the use-case file and throw `InputParseError` on failure. Non-void controllers define a top-level `function presenter(value: XOutput)` and return `Promise<ReturnType<typeof presenter>>` (identity is fine — `return value`); void controllers return `Promise<void>` with no presenter
+- **Feature-scoped tRPC error mapping** — Each feature has `integrations/api/procedures.ts` exporting `xProcedure = t.procedure.use(defineErrorMiddleware([[Ctor, "TRPC_CODE"], ...]))` from `@repo/core-shared/trpc/define-error-middleware`. Routers use `xProcedure.input(xInputSchema)` — schemas are imported from the use-case file, never redefined inline. `core-shared` never enumerates feature error classes
+- **Public surface split** — Feature root (`.`) exports contracts only: types, errors, schemas, IUseCase / IController aliases, router type, constants. UI artifacts (query builders, components) live behind `./ui` (`src/ui/index.ts`). Apps import queries from `@repo/<feature>/ui`, schemas/types from `@repo/<feature>`
 - **Payload repositories via constructor** — Feature packages receive Payload config at constructor time, not as a direct dependency
 - **App bootstrap** — Each app calls `bindProduction*()` per feature at startup to swap mocks for real Payload-backed impls in the InversifyJS containers