diff --git a/scripts/stryker-diff.mjs b/scripts/stryker-diff.mjs
index dd64f4e774..06d06fb7ac 100644
--- a/scripts/stryker-diff.mjs
+++ b/scripts/stryker-diff.mjs
@@ -57,8 +57,14 @@ export const PACKAGE_CONFIGS = [
 		root: "src",
 		sourceRoot: "src/",
 		vitestConfig: "vitest.config.ts",
-		vitestRelated: false,
-		discoverRelatedTests: true,
+		// Use plugin-side related-test discovery for the extension package: with an
+		// explicit STRYKER_TEST_FILES list, stryker-js 10.0.0 plans static mutants with
+		// runtime activation (stryker-mutator/stryker-js#6144, #6209), which the vitest
+		// plugin can only apply after top-level code has run, producing false Survived
+		// results. Revert to vitestRelated: false / discoverRelatedTests: true once the
+		// upstream planner fix lands.
+		vitestRelated: true,
+		discoverRelatedTests: false,
 		// CI build/coverage tooling under src/scripts is excluded like the other build scripts:
 		// it is not shipped runtime code and is covered by src/scripts/__tests__/merge-lcov.spec.mjs.
 		excludedPaths: [
diff --git a/scripts/stryker-diff.test.mjs b/scripts/stryker-diff.test.mjs
index 22284e598d..5286aba38e 100644
--- a/scripts/stryker-diff.test.mjs
+++ b/scripts/stryker-diff.test.mjs
@@ -254,8 +254,11 @@ describe("buildManifest", () => {
 		assert.equal(webview.runRoot, ".")
 		assert.equal(webview.discoverRelatedTests, true)
 		assert.equal(webview.vitestRelated, false)
-		assert.equal(extension.discoverRelatedTests, true)
-		assert.equal(extension.vitestRelated, false)
+		// The extension package deliberately uses plugin-side discovery (see the
+		// comment in PACKAGE_CONFIGS): stryker-js 10.0.0 mis-activates static mutants
+		// when an explicit STRYKER_TEST_FILES list is supplied.
+		assert.equal(extension.discoverRelatedTests, false)
+		assert.equal(extension.vitestRelated, true)
 		const types = manifest.packages.find(({ id }) => id === "types")
 		assert.equal(types.discoverRelatedTests, undefined)
 		assert.equal(types.vitestRelated, undefined)