feat(backend): /settings GET+PUT, /models PiModel shape, app wiring

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

backend/src/routes/meta.ts

@@ -1,14 +1,15 @@
 import { readdirSync } from "node:fs";
 import { join } from "node:path";
 import type { FastifyInstance } from "fastify";
+import type { PiModel } from "../pi/list-models.js";
 
-export type ListModelsFn = () => Promise<string[]>;
+export type ListModelsFn = () => Promise<PiModel[]>;
 
 /**
  * List YAML workspace configs found in <harnessDir>/workspaces/*.yaml.
  * Returns [{name, file}] — no database credentials or secrets.
  */
-function listWorkspaces(harnessDir: string): { name: string; file: string }[] {
+export function listWorkspaces(harnessDir: string): { name: string; file: string }[] {
   const dir = join(harnessDir, "workspaces");
   let entries: string[];
   try {
@@ -18,10 +19,7 @@ function listWorkspaces(harnessDir: string): { name: string; file: string }[] {
   }
   return entries
     .filter((f) => f.endsWith(".yaml") || f.endsWith(".yml"))
-    .map((f) => ({
-      name: f.replace(/\.ya?ml$/, ""),
-      file: f,
-    }));
+    .map((f) => ({ name: f.replace(/\.ya?ml$/, ""), file: f }));
 }
 
 export function metaRoutes(
@@ -32,28 +30,13 @@ export function metaRoutes(
     return listWorkspaces(deps.harnessDir);
   });
 
-  app.get("/models", async (_req, reply) => {
-    const fn = deps.listModels ?? defaultListModels;
+  app.get("/models", async () => {
+    const fn = deps.listModels ?? (async () => []);
     try {
-      const models = await fn();
-      return { models };
+      return { models: await fn() };
     } catch {
       // Graceful fallback: Pi may not be running; don't crash the server.
-      return { models: [] };
+      return { models: [] as PiModel[] };
     }
   });
 }
-
-/**
- * Default implementation: spawns a short-lived `tht` invocation that asks a Pi
- * process for available models via get_available_models.  This is intentionally
- * behind the injectable seam so tests can stub it without spawning real processes.
- *
- * In the MVP we return an empty list — the real spawn path can be wired in later
- * once a Pi-side "list models" RPC stabilises.
- */
-async function defaultListModels(): Promise<string[]> {
-  // Real ephemeral Pi spawn left for a follow-up task.
-  // Returning [] here triggers the graceful fallback seen by clients.
-  return [];
-}

backend/src/routes/settings.ts

@@ -0,0 +1,48 @@
+import type { FastifyInstance } from "fastify";
+import type { AppConfig } from "../config.js";
+import { loadSettings, saveSettings, type Settings } from "../settings/settings-store.js";
+import { listWorkspaces, type ListModelsFn } from "./meta.js";
+
+/** Merge stored settings over env/first-workspace defaults. */
+export function effectiveSettings(cfg: AppConfig, stored: Settings): Settings {
+  const workspaces = listWorkspaces(cfg.harnessDir);
+  return {
+    workspace: stored.workspace ?? (workspaces[0]?.name),
+    provider: stored.provider ?? cfg.defaults.provider,
+    model: stored.model ?? cfg.defaults.model,
+    thinking: stored.thinking ?? cfg.defaults.thinking,
+  };
+}
+
+export function settingsRoutes(
+  app: FastifyInstance,
+  deps: { cfg: AppConfig; listModels: ListModelsFn },
+): void {
+  app.get("/settings", async () => {
+    return effectiveSettings(deps.cfg, loadSettings(deps.cfg));
+  });
+
+  app.put("/settings", async (req, reply) => {
+    const b = (req.body ?? {}) as Settings;
+    if (b.model) {
+      let available: { id: string }[] = [];
+      try {
+        available = await deps.listModels();
+      } catch {
+        available = [];
+      }
+      // Only validate when Pi gave us a non-empty list; otherwise allow (degraded).
+      if (available.length > 0 && !available.some((m) => m.id === b.model)) {
+        return reply.code(400).send({ error: `Unknown model: ${b.model}` });
+      }
+    }
+    const next: Settings = {
+      workspace: b.workspace,
+      provider: b.provider,
+      model: b.model,
+      thinking: b.thinking,
+    };
+    saveSettings(deps.cfg, next);
+    return effectiveSettings(deps.cfg, next);
+  });
+}