chore: make pi-only rpc with fixed sessions

src/agents/index.ts

@@ -1,15 +1,7 @@
-import { claudeSpec } from "./claude.js";
-import { codexSpec } from "./codex.js";
-import { geminiSpec } from "./gemini.js";
-import { opencodeSpec } from "./opencode.js";
 import { piSpec } from "./pi.js";
 import type { AgentKind, AgentSpec } from "./types.js";
 
 const specs: Record<AgentKind, AgentSpec> = {
-  claude: claudeSpec,
-  codex: codexSpec,
-  gemini: geminiSpec,
-  opencode: opencodeSpec,
   pi: piSpec,
 };