diff --git a/test/vitest-unit-fast-config.test.ts b/test/vitest-unit-fast-config.test.ts
index d7bbb24092a7..120a48509862 100644
--- a/test/vitest-unit-fast-config.test.ts
+++ b/test/vitest-unit-fast-config.test.ts
@@ -4,6 +4,8 @@ import { beforeAll, describe, expect, it } from "vitest";
 import { spawnNodeEvalSync } from "../src/test-utils/node-process.js";
 import { cliProcessTestFiles } from "./vitest/vitest.cli-process-paths.mjs";
 import { createCommandsLightVitestConfig } from "./vitest/vitest.commands-light.config.ts";
+import { createContractsPluginVitestConfig } from "./vitest/vitest.contracts-plugin.config.ts";
+import { pluginContractPatterns } from "./vitest/vitest.contracts-shared.ts";
 import { createPluginSdkLightVitestConfig } from "./vitest/vitest.plugin-sdk-light.config.ts";
 import { createUnitFastFakeTimersVitestConfig } from "./vitest/vitest.unit-fast-fake-timers.config.ts";
 import { createUnitFastIsolatedVitestConfig } from "./vitest/vitest.unit-fast-isolated.config.ts";
@@ -196,6 +198,44 @@ describe("unit-fast vitest lane", () => {
     expect(testConfig.include).toContain("src/commands/status-overview-values.test.ts");
   });
 
+  it("keeps excluded stateful files out of directory-scoped CLI runs", () => {
+    // A directory argument must narrow the curated inventory, never replace it with the
+    // directory glob. The lane is non-isolated, so re-admitting an excluded stateful file
+    // pollutes whichever unrelated files share its worker.
+    const otherLaneFiles = new Set([
+      ...getUnitFastTimerTestFiles(),
+      ...getUnitFastIsolatedTestFiles(),
+    ]);
+    for (const dir of ["src/plugins", "src/agents", "src/commands"]) {
+      const testConfig = requireTestConfig(
+        createUnitFastVitestConfig({}, { argv: ["node", "vitest", "run", dir] }),
+      );
+      const include = testConfig.include as string[];
+      const expected = unitFastTestFiles.filter(
+        (file) => file.startsWith(`${dir}/`) && !otherLaneFiles.has(file),
+      );
+
+      expect(include, dir).toEqual(expected);
+      expect(
+        include.filter((entry) => !isUnitFastTestFile(entry)),
+        `${dir} admitted non-unit-fast entries`,
+      ).toEqual([]);
+    }
+
+    const pluginsInclude = requireTestConfig(
+      createUnitFastVitestConfig({}, { argv: ["node", "vitest", "run", "src/plugins"] }),
+    ).include as string[];
+    expect(isUnitFastTestFile("src/plugins/install-persistence.test.ts")).toBe(false);
+    expect(pluginsInclude).not.toContain("src/plugins/install-persistence.test.ts");
+
+    // Glob-scoped lanes keep their own scope too: a parent-directory argument must not widen
+    // contracts-plugin from `contracts/` to every sibling test under `src/plugins`.
+    const contractsInclude = requireTestConfig(
+      createContractsPluginVitestConfig({}, ["node", "vitest", "run", "src/plugins"]),
+    ).include as string[];
+    expect(contractsInclude).toEqual(pluginContractPatterns);
+  });
+
   it("keeps obvious stateful files out of the unit-fast lane", () => {
     expect(isUnitFastTestFile("src/plugin-sdk/temp-path.test.ts")).toBe(false);
     expect(isUnitFastTestFile("src/agents/openai-transport-stream.base.test.ts")).toBe(false);
diff --git a/test/vitest/vitest.pattern-file.ts b/test/vitest/vitest.pattern-file.ts
index dd6016b7e381..3b45f99f6109 100644
--- a/test/vitest/vitest.pattern-file.ts
+++ b/test/vitest/vitest.pattern-file.ts
@@ -132,13 +132,23 @@ function narrowIncludePatterns(
     return null;
   }
 
-  return [
-    ...new Set(
-      candidatePatterns.filter((value) =>
-        includePatterns.some((pattern) => patternsCouldOverlap(value, pattern)),
-      ),
-    ),
-  ];
+  // Narrowing must intersect the CLI selection with the lane's own scope. When the lane is
+  // rooted deeper than the CLI selection, keep the lane: returning the caller's broader
+  // directory pattern re-admits files the lane never owns — `unit-fast` picks up the stateful
+  // files it excludes, and `contracts-*` picks up every sibling test outside `contracts/`.
+  // Both run `isolate: false`, so those extra files share a worker and pollute unrelated ones.
+  const narrowed = new Set<string>();
+  for (const candidate of candidatePatterns) {
+    const candidatePrefix = literalPrefixForGlobPattern(candidate);
+    for (const laneScope of includePatterns) {
+      if (!patternsCouldOverlap(candidate, laneScope)) {
+        continue;
+      }
+      const laneScopePrefix = literalPrefixForGlobPattern(laneScope);
+      narrowed.add(laneScopePrefix.length > candidatePrefix.length ? laneScope : candidate);
+    }
+  }
+  return [...narrowed];
 }
 
 function isPlainRepoRelativePath(value: string): boolean {