fix: preserve custom provider smoke config

backend/test/pi-provider-smoke.test.ts

@@ -24,6 +24,83 @@ function rpcChild(onCommand: (command: any, emit: (message: unknown) => void) =>
   return child;
 }
 
+// Catches an isolated smoke agent that copies auth.json but drops the selected custom
+// provider/model from models.json, causing set_model to fail before the real request.
+test("provider smoke reaches the selected custom provider from an isolated models.json", async () => {
+  let isolatedAgentDir: string | undefined;
+  let providerRequests = 0;
+  const child = rpcChild((command, emit) => {
+    if (command.type === "set_model") {
+      const models = JSON.parse(readFileSync(`${isolatedAgentDir}/models.json`, "utf8"));
+      const selectedProvider = models.providers?.[command.provider];
+      const selectedModel = selectedProvider?.models?.find(
+        (candidate: { id?: unknown }) => candidate.id === command.modelId,
+      );
+      emit({ type: "response", id: command.id, success: Boolean(selectedModel) });
+    }
+    if (command.type === "set_thinking_level") {
+      emit({ type: "response", id: command.id, success: true });
+    }
+    if (command.type === "prompt") {
+      providerRequests++;
+      emit({
+        type: "message_end",
+        message: { role: "assistant", stopReason: "stop", content: "must-not-be-returned" },
+      });
+      emit({
+        type: "agent_end",
+        messages: [{ role: "assistant", stopReason: "stop", content: "must-not-be-returned" }],
+      });
+    }
+  });
+  const smoke = createPiProviderSmoke(loadConfig({ PI_BIN: "/usr/local/bin/pi" }), {
+    spawnFn: (_command, _args, options) => {
+      isolatedAgentDir = options.env.PI_CODING_AGENT_DIR;
+      expect(readdirSync(isolatedAgentDir)).toEqual(["auth.json", "models.json"]);
+      expect(JSON.parse(readFileSync(`${isolatedAgentDir}/models.json`, "utf8"))).toEqual({
+        providers: {
+          "custom-openai": {
+            baseUrl: "https://selected.invalid/v1",
+            api: "openai-completions",
+            models: [{ id: "selected-model", name: "Selected model", reasoning: true }],
+          },
+        },
+      });
+      return child;
+    },
+    authProviders: () => new Set(["custom-openai"]),
+    readAuthStore: () => JSON.stringify({
+      "custom-openai": { type: "api_key", key: "test-only" },
+      unrelated: { type: "api_key", key: "must-not-enter-isolated-context" },
+    }),
+    readModelsStore: () => JSON.stringify({
+      providers: {
+        "custom-openai": {
+          baseUrl: "https://selected.invalid/v1",
+          api: "openai-completions",
+          models: [
+            { id: "selected-model", name: "Selected model", reasoning: true },
+            { id: "unrelated-model", name: "Must not enter isolated context" },
+          ],
+        },
+        unrelated: {
+          baseUrl: "https://unrelated.invalid/v1",
+          api: "openai-completions",
+          apiKey: "!must-not-run",
+          models: [{ id: "unrelated-model" }],
+        },
+      },
+    }),
+  });
+
+  await expect(smoke({
+    provider: "custom-openai", model: "selected-model", reasoning: "medium", timeoutMs: 750,
+  })).resolves.toBeUndefined();
+  expect(providerRequests).toBe(1);
+  expect(child.kill).toHaveBeenCalledOnce();
+  expect(isolatedAgentDir && existsSync(dirname(isolatedAgentDir))).toBe(false);
+});
+
 // Catches a provider smoke process that runs from the trusted harness or leaves Pi tools,
 // extensions, skills, context files, templates, themes, or session persistence enabled.
 test("provider smoke makes one configured request from an isolated no-capability Pi process", async () => {
@@ -71,6 +148,7 @@ test("provider smoke makes one configured request from an isolated no-capability
       zai: { type: "api_key", key: "test-only" },
       deepseek: { type: "api_key", key: "must-not-enter-isolated-context" },
     }),
+    readModelsStore: () => undefined,
   });
 
   await expect(smoke({
@@ -144,6 +222,7 @@ test.each(unexpectedToolEvents)("provider smoke fails closed on an unexpected $n
     spawnFn: () => child,
     authProviders: () => new Set(["zai"]),
     readAuthStore: () => '{"zai":{"type":"api_key","key":"test-only"}}',
+    readModelsStore: () => undefined,
   });
 
   await expect(smoke({
@@ -174,6 +253,7 @@ test("provider smoke rejects a failed model turn with a stable non-secret error"
     spawnFn: () => child,
     authProviders: () => new Set(["zai"]),
     readAuthStore: () => '{"zai":{"type":"api_key","key":"test-only"}}',
+    readModelsStore: () => undefined,
   });
 
   let caught: unknown;