fix(core-typescript): tighten jsdom config tests + document cycle avoidance

- Replace arrayContaining with toEqual on setupFiles + include — captures
  actual mergeConfig array-concatenation behavior so future changes to
  setup/node.ts surface in this test.
- Document in core-typescript/AGENTS.md why @repo/core-testing is not a
  devDep here (would create a circular dependency with core-testing).

Reviewer: superpowers:code-reviewer (Task 2 of Plan 7).

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

packages/core-typescript/AGENTS.md

@@ -4,6 +4,15 @@
 
 Shared TypeScript base configs (`tsconfig.json` files) and Vitest base config, consumed by all packages.
 
+## Why `@repo/core-testing` is not a devDependency here
+
+Plan 7 Step 9 originally said to add it. Doing so creates a circular dependency
+because `@repo/core-testing` already depends on `@repo/core-typescript` for its
+own tsconfig. The base configs reference `@repo/core-testing/setup/{node,jsdom}`
+as STRING paths in `setupFiles` — these are resolved at Vitest execution time
+by the consuming feature package, not by `core-typescript` itself. Each feature
+package therefore lists `@repo/core-testing` in its own `devDependencies`.
+
 ## What it owns
 
 - **`base.json`** — Base `tsconfig.json`: target ES2022, module ESM, `experimentalDecorators` + `emitDecoratorMetadata` for InversifyJS

packages/core-typescript/vitest.base.jsdom.test.ts

@@ -1,19 +1,30 @@
 import { describe, it, expect } from "vitest";
 import { jsdomVitestConfig } from "./vitest.base.jsdom";
 
+// jsdomVitestConfig is built with mergeConfig(nodeVitestConfig, ...).
+// mergeConfig concatenates arrays rather than replacing them, so:
+//   - setupFiles inherits the node setup file (currently a no-op) AND adds the jsdom one
+//   - include inherits the node patterns AND adds the tsx-aware patterns (the file globs deduplicate at resolution)
+// We assert the EXACT merged arrays so any future change to setup/node.ts or to include
+// behavior is consciously visible in this test.
+
 describe("jsdomVitestConfig", () => {
   it("uses jsdom environment", () => {
     expect(jsdomVitestConfig.test?.environment).toBe("jsdom");
   });
-  it("loads the jsdom setup file", () => {
+  it("loads both the node setup (no-op) and jsdom setup files", () => {
-    expect(jsdomVitestConfig.test?.setupFiles).toEqual(
+    expect(jsdomVitestConfig.test?.setupFiles).toEqual([
-      expect.arrayContaining(["@repo/core-testing/setup/jsdom"]),
+      "@repo/core-testing/setup/node",
-    );
+      "@repo/core-testing/setup/jsdom",
+    ]);
   });
-  it("includes tsx files", () => {
+  it("merges include globs from node base with the tsx-aware patterns", () => {
-    expect(jsdomVitestConfig.test?.include).toEqual(
+    expect(jsdomVitestConfig.test?.include).toEqual([
-      expect.arrayContaining(["src/**/*.test.{ts,tsx}", "tests/**/*.test.{ts,tsx}"]),
+      "src/**/*.test.ts",
-    );
+      "tests/**/*.test.ts",
+      "src/**/*.test.{ts,tsx}",
+      "tests/**/*.test.{ts,tsx}",
+    ]);
   });
   it("inherits clearMocks from node base", () => {
     expect(jsdomVitestConfig.test?.clearMocks).toBe(true);