test(router-eval): give spawned CLI children an explicit DATA_DIR

The router-eval CLI test spawns the CLI with spawnSync and asserts stderr stays empty. NODE_TEST_CONTEXT is inherited by those children, so since #10432 (guard #10428) resolveWritableDataDir() detects a test context with no DATA_DIR and warns on stderr before falling back to a throwaway dir - 194 chars that broke three cases. Pass an isolated DATA_DIR in the child env (the resolution the guard message itself prescribes) instead of loosening the assertions.

tests/unit/router-eval-cli.test.ts

@@ -8,7 +8,7 @@
 // limitation, not a defect in the code under test: the OmniRoute runtime itself
 // cascades to node:sqlite/sql.js when better-sqlite3 is unavailable. See
 // tests/unit/_helpers/betterSqlite3Availability.ts for a guard helper.
-import test from "node:test";
+import test, { after } from "node:test";
 import assert from "node:assert/strict";
 import { mkdtempSync, readFileSync, writeFileSync, rmSync } from "node:fs";
 import { tmpdir } from "node:os";
@@ -18,9 +18,19 @@ import Database from "better-sqlite3";
 
 const scriptPath = "scripts/router-eval/index.ts";
 
+// #10432 (guard #10428) made every process that detects a test context but has no
+// explicit DATA_DIR warn on stderr before falling back to a throwaway dir.
+// `NODE_TEST_CONTEXT` is inherited by the children spawned below, so the CLI printed
+// that warning and broke the "stderr stays empty" assertions. Give every child its own
+// DATA_DIR — the exact resolution the guard message prescribes — instead of loosening
+// the assertions.
+const cliDataDir = mkdtempSync(join(tmpdir(), "router-eval-cli-datadir-"));
+after(() => rmSync(cliDataDir, { recursive: true, force: true }));
+
 function runCli(args: string[]) {
   return spawnSync(process.execPath, ["--import", "tsx", scriptPath, ...args], {
     encoding: "utf8",
+    env: { ...process.env, DATA_DIR: cliDataDir },
   });
 }