feat(backend): ephemeral Pi model lister (get_available_models) with TTL cache

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

backend/src/pi/list-models.ts

@@ -0,0 +1,63 @@
+import { spawn as nodeSpawn, type ChildProcessWithoutNullStreams } from "node:child_process";
+import { join } from "node:path";
+import type { AppConfig } from "../config.js";
+import { RpcClient } from "../rpc/rpc-client.js";
+
+export interface PiModel {
+  provider: string;
+  id: string;
+  name: string;
+  reasoning: boolean;
+}
+
+interface Opts {
+  spawnFn?: () => ChildProcessWithoutNullStreams;
+  ttlMs?: number;
+  nowMs?: () => number;
+}
+
+/**
+ * Returns a function that lists Pi's available models (those with auth
+ * configured) via an ephemeral `pi --mode rpc` process. Result is cached for
+ * `ttlMs`. The returned function rejects on timeout/error; callers degrade.
+ */
+export function createPiModelLister(cfg: AppConfig, opts: Opts = {}): () => Promise<PiModel[]> {
+  const ttlMs = opts.ttlMs ?? 60_000;
+  const now = opts.nowMs ?? (() => Date.now());
+  const spawnFn =
+    opts.spawnFn ??
+    (() => {
+      const harnessVenvBin = join(cfg.harnessDir, ".venv", "bin");
+      return nodeSpawn(cfg.piBin, ["--mode", "rpc"], {
+        cwd: cfg.harnessDir,
+        env: { ...process.env, PATH: `${harnessVenvBin}:${process.env.PATH ?? ""}` },
+      }) as ChildProcessWithoutNullStreams;
+    });
+
+  let cache: { at: number; models: PiModel[] } | null = null;
+
+  return async function listModels(): Promise<PiModel[]> {
+    if (cache && now() - cache.at < ttlMs) return cache.models;
+
+    const child = spawnFn();
+    child.stderr.resume();
+    const rpc = new RpcClient(child);
+    try {
+      const resp = await Promise.race([
+        rpc.request({ type: "get_available_models" }),
+        new Promise<never>((_, rej) => setTimeout(() => rej(new Error("pi model list timeout")), 8000)),
+      ]);
+      const raw = (resp?.data?.models ?? []) as Array<Record<string, unknown>>;
+      const models: PiModel[] = raw.map((m) => ({
+        provider: String(m.provider ?? ""),
+        id: String(m.id ?? ""),
+        name: String(m.name ?? m.id ?? ""),
+        reasoning: Boolean(m.reasoning),
+      }));
+      cache = { at: now(), models };
+      return models;
+    } finally {
+      child.kill();
+    }
+  };
+}