refactor(core-trpc): make the tRPC context router-agnostic

Ports the type-safety/ergonomics half of the upstream cycle-break: core-trpc
no longer imports AppRouter from @repo/core-api (an illegal
core -> core-composition boundary edge). The runtime context and both
providers are now AnyTRPCRouter-generic; consumers inject their router type
via useTRPC<TRouter>().

The clean-slate tree is already cycle-free (no kept feature consumes
core-trpc), so this is purely the architecture/boundary improvement. The
per-feature app-slice types the upstream commit added for the demo features
are intentionally skipped: no kept feature consumes useTRPC yet.

Also covers the router-agnostic useTRPC delegation: the refactor turned
useTRPC into a wrapper function whose body was unexercised, dropping
client.ts below the coverage floor — client.test.ts stubs the context
factory and asserts the delegation, restoring client.ts to 100%.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_016j8z4VHjedXDTjEDNg7qHK

packages/core-trpc/package.json

@@ -15,7 +15,6 @@
     "test": "vitest run --passWithNoTests"
   },
   "dependencies": {
-    "@repo/core-api": "workspace:*",
     "@tanstack/react-query": "^5.66.0",
     "@trpc/client": "^11.18.0",
     "@trpc/server": "^11.18.0",

packages/core-trpc/src/client.test.ts

@@ -1,4 +1,15 @@
-import { describe, it, expect } from "vitest";
+import { describe, it, expect, vi } from "vitest";
+
+// Stub the tRPC context factory so useTRPC() can run outside a React render:
+// the real context.useTRPC() requires a mounted TRPCProvider. The stubbed
+// proxy lets us exercise the router-agnostic delegation (client.ts:useTRPC).
+vi.mock("@trpc/tanstack-react-query", () => ({
+  createTRPCContext: () => ({
+    TRPCProvider: () => null,
+    useTRPC: () => ({ __proxy: "trpc-options-proxy" }),
+  }),
+}));
+
 import { useTRPC, TRPCProvider } from "./client";
 
 describe("core-trpc client exports", () => {
@@ -9,4 +20,10 @@ describe("core-trpc client exports", () => {
   it("exports TRPCProvider component", () => {
     expect(TRPCProvider).toBeTypeOf("function");
   });
+
+  it("useTRPC delegates to the underlying router-agnostic tRPC proxy", () => {
+    // The generic is a compile-time-only cast; at runtime it returns whatever
+    // the shared context proxy yields.
+    expect(useTRPC()).toEqual({ __proxy: "trpc-options-proxy" });
+  });
 });

packages/core-trpc/src/client.ts

@@ -1,6 +1,20 @@
 "use client";
 
 import { createTRPCContext } from "@trpc/tanstack-react-query";
-import type { AppRouter } from "@repo/core-api";
+import type { TRPCOptionsProxy } from "@trpc/tanstack-react-query";
+import type { AnyTRPCRouter } from "@trpc/server";
 
-export const { TRPCProvider, useTRPC } = createTRPCContext<AppRouter>();
+// core-trpc must not depend on @repo/core-api (core → core-composition is an
+// illegal boundary edge and creates a package cycle through the features).
+// The runtime context is router-agnostic; consumers inject their router type
+// as a generic: features pass their app-slice type (e.g. `BlogAppSlice`),
+// apps may pass the full AppRouter.
+const context = createTRPCContext<AnyTRPCRouter>();
+
+export const TRPCProvider = context.TRPCProvider;
+
+export function useTRPC<
+  TRouter extends AnyTRPCRouter = AnyTRPCRouter,
+>(): TRPCOptionsProxy<TRouter> {
+  return context.useTRPC() as unknown as TRPCOptionsProxy<TRouter>;
+}

packages/core-trpc/src/index.ts

@@ -1,3 +1,2 @@
 export { useTRPC, TRPCProvider } from "./client";
 export { getQueryClient } from "./query-client";
-export type { AppRouter } from "@repo/core-api";

packages/core-trpc/src/providers/next-provider.tsx

@@ -4,7 +4,7 @@ import { useState } from "react";
 import { QueryClientProvider } from "@tanstack/react-query";
 import { createTRPCClient, httpBatchLink } from "@trpc/client";
 import superjson from "superjson";
-import type { AppRouter } from "@repo/core-api";
+import type { AnyTRPCRouter } from "@trpc/server";
 import { TRPCProvider } from "../client";
 import { getQueryClient } from "../query-client";
 
@@ -22,7 +22,9 @@ export function NextTrpcProvider({
 }) {
   const [queryClient] = useState(() => getQueryClient());
   const [trpcClient] = useState(() =>
-    createTRPCClient<AppRouter>({
+    // Router-agnostic on purpose: procedure typing comes from useTRPC<TRouter>
+    // at the call sites, not from the wire-level client.
+    createTRPCClient<AnyTRPCRouter>({
       links: [
         httpBatchLink({
           url: `${getBaseUrl()}${trpcUrl}`,

packages/core-trpc/src/providers/tanstack-provider.tsx

@@ -4,7 +4,7 @@ import { useState } from "react";
 import { QueryClientProvider } from "@tanstack/react-query";
 import { createTRPCClient, httpBatchLink } from "@trpc/client";
 import superjson from "superjson";
-import type { AppRouter } from "@repo/core-api";
+import type { AnyTRPCRouter } from "@trpc/server";
 import { TRPCProvider } from "../client";
 import { getQueryClient } from "../query-client";
 
@@ -17,7 +17,9 @@ export function TanstackTrpcProvider({
 }) {
   const [queryClient] = useState(() => getQueryClient());
   const [trpcClient] = useState(() =>
-    createTRPCClient<AppRouter>({
+    // Router-agnostic on purpose: procedure typing comes from useTRPC<TRouter>
+    // at the call sites, not from the wire-level client.
+    createTRPCClient<AnyTRPCRouter>({
       links: [httpBatchLink({ url: trpcUrl, transformer: superjson })],
     }),
   );

pnpm-lock.yaml

@@ -760,9 +760,6 @@ importers:
 
   packages/core-trpc:
     dependencies:
-      "@repo/core-api":
-        specifier: workspace:*
-        version: link:../core-api
       "@tanstack/react-query":
         specifier: ^5.66.0
         version: 5.96.2(react@19.2.4)