refactor: add execution backend selection

tests/execution-backend-selector.test.ts

@@ -0,0 +1,75 @@
+import assert from "node:assert/strict";
+import test from "node:test";
+import { selectExecutionBackendForTesting } from "@/lib/execution/backend-selector";
+
+test("selectExecutionBackendForTesting prefers the ready primary master codex node", async () => {
+  const backend = await selectExecutionBackendForTesting({
+    primary: { provider: "master_codex_node", status: "ready" },
+    backups: [
+      { provider: "aliyun_qwen_api", status: "ready" },
+      { provider: "openai_api", status: "ready" },
+    ],
+  });
+
+  assert.equal(backend.backendId, "master-codex-node");
+});
+
+test("selectExecutionBackendForTesting falls back to ready aliyun qwen before openai", async () => {
+  const backend = await selectExecutionBackendForTesting({
+    primary: { provider: "master_codex_node", status: "degraded" },
+    backups: [
+      { provider: "openai_api", status: "ready" },
+      { provider: "aliyun_qwen_api", status: "ready" },
+    ],
+  });
+
+  assert.equal(backend.backendId, "aliyun-qwen");
+});
+
+test("selectExecutionBackendForTesting falls back to ready openai when aliyun qwen is unavailable", async () => {
+  const backend = await selectExecutionBackendForTesting({
+    primary: { provider: "master_codex_node", status: "degraded" },
+    backups: [
+      { provider: "openai_api", status: "ready" },
+      { provider: "aliyun_qwen_api", status: "disabled" },
+    ],
+  });
+
+  assert.equal(backend.backendId, "openai-api");
+});
+
+test("selectExecutionBackendForTesting uses fixed backend order when an API primary is not ready", async () => {
+  const backend = await selectExecutionBackendForTesting({
+    primary: { provider: "openai_api", status: "degraded" },
+    backups: [
+      { provider: "master_codex_node", status: "ready" },
+      { provider: "aliyun_qwen_api", status: "ready" },
+    ],
+  });
+
+  assert.equal(backend.backendId, "aliyun-qwen");
+});
+
+test("selectExecutionBackendForTesting does not let an earlier disabled backup hide a later ready account", async () => {
+  const backend = await selectExecutionBackendForTesting({
+    primary: { provider: "master_codex_node", status: "degraded" },
+    backups: [
+      { provider: "openai_api", status: "disabled" },
+      { provider: "openai_api", status: "ready" },
+    ],
+  });
+
+  assert.equal(backend.backendId, "openai-api");
+});
+
+test("selectExecutionBackendForTesting falls back to master node last when higher-priority API backends are unavailable", async () => {
+  const backend = await selectExecutionBackendForTesting({
+    primary: { provider: "openai_api", status: "degraded" },
+    backups: [
+      { provider: "aliyun_qwen_api", status: "disabled" },
+      { provider: "master_codex_node", status: "ready" },
+    ],
+  });
+
+  assert.equal(backend.backendId, "master-codex-node");
+});