diff --git a/test/scripts/changed-lanes.test.ts b/test/scripts/changed-lanes.test.ts
index 1e7bc57fea2..997c0a2a38e 100644
--- a/test/scripts/changed-lanes.test.ts
+++ b/test/scripts/changed-lanes.test.ts
@@ -172,6 +172,33 @@ describe("scripts/changed-lanes", () => {
     expect(plan.runFullTests).toBe(false);
   });
 
+  it("keeps shared Vitest wiring changes on the broad changed test path", () => {
+    const result = detectChangedLanes(["test/vitest/vitest.shared.config.ts"]);
+    const plan = createChangedCheckPlan(result);
+
+    expect(plan.testTargets).toEqual([]);
+    expect(plan.runChangedTestsBroad).toBe(true);
+    expect(plan.runFullTests).toBe(false);
+  });
+
+  it("keeps setup changes on the broad changed test path", () => {
+    const result = detectChangedLanes(["test/setup.ts"]);
+    const plan = createChangedCheckPlan(result);
+
+    expect(plan.testTargets).toEqual([]);
+    expect(plan.runChangedTestsBroad).toBe(true);
+    expect(plan.runFullTests).toBe(false);
+  });
+
+  it("routes changed extension Vitest configs to only their owning shard", () => {
+    const result = detectChangedLanes(["test/vitest/vitest.extension-discord.config.ts"]);
+    const plan = createChangedCheckPlan(result);
+
+    expect(plan.testTargets).toEqual(["test/vitest/vitest.extension-discord.config.ts"]);
+    expect(plan.runChangedTestsBroad).toBe(false);
+    expect(plan.runFullTests).toBe(false);
+  });
+
   it("keeps an empty changed path list as a no-op", () => {
     const result = detectChangedLanes([]);
     const plan = createChangedCheckPlan(result);
@@ -189,6 +216,7 @@ describe("scripts/changed-lanes", () => {
     expect(plan.commands).toEqual([
       { name: "conflict markers", args: ["check:no-conflict-markers"] },
     ]);
+    expect(plan.runChangedTestsBroad).toBe(false);
     expect(plan.runFullTests).toBe(false);
   });
 
@@ -200,6 +228,7 @@ describe("scripts/changed-lanes", () => {
     expect(plan.commands).toEqual([
       { name: "conflict markers", args: ["check:no-conflict-markers"] },
     ]);
+    expect(plan.runChangedTestsBroad).toBe(false);
     expect(plan.runFullTests).toBe(false);
   });
 });
diff --git a/test/scripts/test-projects.test.ts b/test/scripts/test-projects.test.ts
index 2c0fef40c48..b3ec76b82f6 100644
--- a/test/scripts/test-projects.test.ts
+++ b/test/scripts/test-projects.test.ts
@@ -6,6 +6,7 @@ import {
   buildVitestRunPlans,
   listFullExtensionVitestProjectConfigs,
   shouldAcquireLocalHeavyCheckLock,
+  resolveChangedTestTargetPlan,
   resolveChangedTargetArgs,
   resolveParallelFullSuiteConcurrency,
 } from "../../scripts/test-projects.test-support.mjs";
@@ -29,6 +30,20 @@ describe("scripts/test-projects changed-target routing", () => {
     ).toBeNull();
   });
 
+  it("keeps test runner implementation edits on runner tests", () => {
+    expect(
+      resolveChangedTestTargetPlan([
+        "scripts/check-changed.mjs",
+        "scripts/test-projects.test-support.d.mts",
+        "scripts/test-projects.test-support.mjs",
+        "test/scripts/changed-lanes.test.ts",
+      ]),
+    ).toEqual({
+      mode: "targets",
+      targets: ["test/scripts/changed-lanes.test.ts", "test/scripts/test-projects.test.ts"],
+    });
+  });
+
   it("routes changed extension vitest configs to their own shard", () => {
     expect(
       buildVitestRunPlans(["--changed", "origin/main"], process.cwd(), () => [