feat(backend): support container runtime paths

backend/src/pi/list-models.ts

@@ -1,5 +1,4 @@
 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";
 
@@ -11,7 +10,11 @@ export interface PiModel {
 }
 
 interface Opts {
-  spawnFn?: () => ChildProcessWithoutNullStreams;
+  spawnFn?: (
+    command: string,
+    args: string[],
+    options: { cwd: string; env: NodeJS.ProcessEnv },
+  ) => ChildProcessWithoutNullStreams;
   ttlMs?: number;
   nowMs?: () => number;
 }
@@ -24,22 +27,16 @@ interface Opts {
 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;
-    });
+  const spawnFn = opts.spawnFn ?? nodeSpawn;
 
   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();
+    const env: NodeJS.ProcessEnv = { ...process.env };
+    if (cfg.dataRoot !== undefined) env.THT_DATA_ROOT = cfg.dataRoot;
+    const child = spawnFn(cfg.piBin, ["--mode", "rpc"], { cwd: cfg.harnessDir, env });
     child.stderr.resume();
     const rpc = new RpcClient(child);
     try {