fix(rpc): close prototype-chain permission bypass, add server/client/transport tests

C1 CRITICAL: implement() looked up procedures/handlers with plain property
indexing, so any Object.prototype member name (constructor, toString, etc.)
resolved truthy and skipped the permission gate entirely. Fixed with
Object.hasOwn checks in packages/rpc/src/server.ts. Defense-in-depth guard
added in packages/dev-server/src/rpc-dispatch.ts constraining URL path
segments to a safe charset before they reach service/procedure lookups.

Added missing direct test coverage for packages/rpc/src/transport.ts,
server.ts and client.ts (previously untested), including a prototype-name
sweep in both server.test.ts and dev-server's rpc-endpoint.test.ts.

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

packages/rpc/src/server.ts

@@ -37,8 +37,14 @@ export function implement<Procedures extends AnyProcedures>(
   return {
     contract,
     async invoke(procedureName, payload, identity) {
-      const definition = contract.procedures[procedureName as keyof Procedures];
-      const handler = handlers[procedureName as keyof Procedures];
+      // Object.hasOwn, not plain indexing: "constructor", "toString" and every
+      // other Object.prototype member otherwise resolve as truthy, and a
+      // prototype member carries no `permission`, so the gate below is skipped
+      // entirely and an unintended function runs with attacker-controlled input.
+      const known =
+        Object.hasOwn(contract.procedures, procedureName) && Object.hasOwn(handlers, procedureName);
+      const definition = known ? contract.procedures[procedureName as keyof Procedures] : undefined;
+      const handler = known ? handlers[procedureName as keyof Procedures] : undefined;
       if (!definition || !handler) return failure(RPC_ERROR_CODES.unknown, "Unknown procedure");
 
       let subject: SubjectContext | undefined;