fix(rpc): close the service-collision fail-open and the fix-wave gaps

Critical:
- router: fail loudly (WRN-SERVICE-COLLISION) when two app/services files
  scan to the same service name, instead of silently letting directory-walk
  order pick a winner.

Important:
- server.ts: wrap a throwing input schema so its raw message cannot escape
  invoke(); returns RPC_INVALID and logs server-side instead.
- client.ts: race timeoutMs against transport.call so a stalled transport
  cannot hang the caller; rejects with a ServiceError(RPC_TRANSPORT).
- client.ts: the proxy returns undefined for undeclared properties (incl.
  then/catch/finally) instead of a function that throws, closing the
  await-client thenable trap.
- gateway.ts / rpc-dispatch.ts: import RPC_PATH_PREFIX / RPC_INTERNAL_HEADER
  from @wrnexus/rpc instead of hardcoding local copies.
- gateway.test.ts: cover the RPC-prefix edge block and internal-header
  stripping across casing variants.
- http.test.ts / client.test.ts: cover anonymous-call header omission, the
  internal marker, the retryable-status sweep, network/malformed/HTML
  failures, AbortSignal propagation, the timeout path, and timer cleanup.

Minor:
- transport.ts: Object.hasOwn for handler lookup; note the entry-only abort
  check.
- client.ts: wrap a missing/invalid WRNEXUS_RPC_SECRET as a ServiceError
  (RPC_IDENTITY) instead of a bare Error.
- rpc/package.json: drop the unused @wrnexus/authz dependency.
- server.ts: implement() now throws at construction time if a declared
  procedure has no own handler.

Verified: reverting the service-collision check and the client timeout race
each make their new test fail, then restore green.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

packages/dev-server/test/gateway.test.ts

@@ -1,4 +1,5 @@
 import { expect, test } from "bun:test";
+import { RPC_INTERNAL_HEADER, RPC_PATH_PREFIX } from "@wrnexus/rpc";
 import {
   defaultGatewayHostname,
   forwardAuthFailure,
@@ -7,6 +8,7 @@ import {
   stripUntrustedInternalHeaders,
   gatewayRestartDelay,
   internalError,
+  isRpcGatewayPath,
   stripInternalError,
 } from "../src/gateway.ts";
 import { resolveProductionHostname } from "../src/prod.ts";
@@ -144,6 +146,29 @@ test("nested SSO proxy keeps the protected app's original request headers", () =
   expect(proxied.get("x-original-uri")).toBe("/settings");
 });
 
+test("the reserved RPC prefix is refused at the gateway before any proxying", () => {
+  expect(isRpcGatewayPath(RPC_PATH_PREFIX)).toBe(true);
+  expect(isRpcGatewayPath(`${RPC_PATH_PREFIX}/billing/createInvoice`)).toBe(true);
+  expect(isRpcGatewayPath("/api/billing")).toBe(false);
+  expect(isRpcGatewayPath("/__wrnexus/rpcfoo")).toBe(false);
+});
+
+test("an inbound internal-marker header from outside is stripped regardless of casing", () => {
+  for (const name of [
+    RPC_INTERNAL_HEADER,
+    RPC_INTERNAL_HEADER.toUpperCase(),
+    "X-WrNexus-Internal",
+  ]) {
+    const request = new Request("http://localhost:3000/path", {
+      headers: { [name]: "1" },
+    });
+    const headers = stripUntrustedInternalHeaders(
+      gatewayProxyHeaders(request, new URL(request.url), "127.0.0.1", true),
+    );
+    expect(headers.has(RPC_INTERNAL_HEADER)).toBe(false);
+  }
+});
+
 test("gateway respawns development apps after an HMR restart exit", () => {
   expect(gatewayRestartDelay("development", 97, null)).toBe(0);
   expect(gatewayRestartDelay("development", 1, null)).toBe(1200);