test(mutation): configure mutation testing with vitest integration

- Add vitest-runner plugin to stryker configuration
- Create custom vitest.mutation.config.ts to exclude slow tests
- Set coverageAnalysis to 'off' for faster mutation testing
- Remove incompatible typescript checker configuration
- Configure to run only validation tests (exclude *.exp.*.test.ts)
- Set 60s timeout for mutation test execution
- Update concurrency setting from maxConcurrentTestRunners

This enables mutation testing to run successfully on test infrastructure,
validating test effectiveness by injecting code mutations and verifying
tests fail appropriately.

Author: Mearman

stryker.config.json

@@ -1,8 +1,14 @@
 {
   "$schema": "./node_modules/@stryker-mutator/core/schema/stryker-schema.json",
   "packageManager": "pnpm",
+  "plugins": [
+    "@stryker-mutator/vitest-runner"
+  ],
   "testRunner": "vitest",
-  "coverageAnalysis": "perTest",
+  "vitest": {
+    "configFile": "vitest.mutation.config.ts"
+  },
+  "coverageAnalysis": "off",
   "mutate": [
     "src/experiments/evaluation/__tests__/validation/common/benchmark-graph-expander.ts",
     "src/experiments/evaluation/__tests__/validation/common/test-graph-expander.ts",
@@ -12,7 +18,6 @@
     "src/experiments/evaluation/metrics/structural-representativeness.ts"
   ],
   "mutator": {
-    "plugins": ["@stryker-mutator/typescript-checker"],
     "excludedMutations": [
       "StringLiteral",
       "BlockStatement"
@@ -33,8 +38,7 @@
   },
   "timeoutMS": 300000,
   "timeoutFactor": 1.5,
-  "maxConcurrentTestRunners": 2,
+  "concurrency": 2,
   "disableTypeChecks": "{test,src,lib}/**/*.{js,ts,jsx,tsx,html,vue}",
-  "checkers": ["typescript"],
   "tsconfigFile": "tsconfig.json"
 }

vitest.mutation.config.ts

@@ -0,0 +1,23 @@
+import { defineConfig } from "vitest/config";
+import tsconfigPaths from "vite-tsconfig-paths";
+
+export default defineConfig({
+	plugins: [tsconfigPaths()],
+	test: {
+		globals: true,
+		environment: "node",
+		fileParallelism: false,
+		testTimeout: 60000, // 60 seconds for mutation testing
+		include: [
+			"src/experiments/evaluation/__tests__/validation/common/*.unit.test.ts",
+			"src/experiments/evaluation/__tests__/validation/*.unit.test.ts",
+			"src/experiments/evaluation/metrics/*.property.unit.test.ts",
+		],
+		exclude: [
+			"node_modules",
+			"dist",
+			"**/*.exp.*.test.ts", // Exclude expensive experimental tests
+			"**/*.integration.test.ts", // Exclude slow integration tests  except validation
+		],
+	},
+});