diff --git a/docs/superpowers/plans/2026-08-14-cl10-final-review-closure.md b/docs/superpowers/plans/2026-08-14-cl10-final-review-closure.md
index 114f448c12..b5eb331317 100644
--- a/docs/superpowers/plans/2026-08-14-cl10-final-review-closure.md
+++ b/docs/superpowers/plans/2026-08-14-cl10-final-review-closure.md
@@ -22,10 +22,19 @@ A direct same-publisher bundle revocation whose target bundle is absent is norma
 
 The closure is protected by focused tests that require:
 
-- live lock contention to return `community_cache_busy` in under 500 ms;
+- live lock contention to throw `community_cache_busy` synchronously without running protected work;
+- one signal-zero owner-liveness check on that refusal, rejecting repeated live-owner polling;
 - the management community endpoint to return `503` plus `Retry-After: 1` for that contention;
+- both rejection paths to preserve the existing owner bytes and lock directory identity;
 - oversized locally-originated community copies to be removed during sensitive purge;
 - hardlinked locally-originated cache pathnames to be removed while a peer hardlink survives; and
 - missing direct revocation bundle targets to return stable `revocation_target` errors.
 
+The contention tests originally required completion in under 500 ms. That wall-clock criterion
+included filesystem and management-route work and could fail under shared CI load before checking
+the actual response contract. Verification now checks synchronous refusal, one owner-liveness probe,
+and ownership preservation under the normal test deadline. The probe count detects repeated owner
+checks, but does not promise to detect an unrelated one-off delay. This changes the test oracle, not the fail-fast/no-polling runtime
+contract above, and does not establish a new response-time SLA.
+
 Exact-head GitHub Actions success is required before this closure is considered verified. PR #1510 must remain open and unmerged during this review cycle.
diff --git a/tests/lab/lab-community-mutation-lock.test.ts b/tests/lab/lab-community-mutation-lock.test.ts
index ced17392a0..7c3132d155 100644
--- a/tests/lab/lab-community-mutation-lock.test.ts
+++ b/tests/lab/lab-community-mutation-lock.test.ts
@@ -1,5 +1,5 @@
-import { afterEach, describe, expect, test } from "bun:test";
-import { existsSync, mkdirSync, mkdtempSync, utimesSync, writeFileSync } from "node:fs";
+import { afterEach, describe, expect, spyOn, test } from "bun:test";
+import { existsSync, lstatSync, mkdirSync, mkdtempSync, readFileSync, utimesSync, writeFileSync } from "node:fs";
 import { tmpdir } from "node:os";
 import { join } from "node:path";
 import { ensureLabDirs, labCommunityDir } from "../../src/lab/paths";
@@ -7,6 +7,7 @@ import { listCommunityEvidence } from "../../src/lab/public/community";
 import {
   publicEvidenceMutationLockIsReclaimableForTests,
   publicEvidenceTryReclaimMutationLockForTests,
+  withPublicEvidenceMutationLock,
 } from "../../src/lab/public/mutation-lock";
 import { PublicEvidenceValidationError } from "../../src/lab/public/validate";
 import { removeTreeWithRetry } from "../helpers/remove-tree";
@@ -69,23 +70,35 @@ describe("community mutation lock", () => {
     expect(existsSync(lockPath)).toBe(true);
   });
 
-  test("fails fast when a live owner holds the mutation lock", () => {
+  test("rejects a live owner after one check without running protected work or changing ownership", () => {
     const config = configDir();
     const lockPath = createLiveOwnerLock(config);
-    const startedAt = performance.now();
+    const lockBefore = lstatSync(lockPath);
+    const ownerBefore = readFileSync(join(lockPath, "owner.json"));
+    let ranProtectedWork = false;
     let failure: unknown;
 
+    // Observe the real signal-zero owner check. A retry loop must not poll a
+    // live owner before eventually returning the same refusal.
+    const ownerCheck = spyOn(process, "kill");
     try {
-      listCommunityEvidence(config);
-    } catch (error) {
-      failure = error;
+      try {
+        withPublicEvidenceMutationLock(config, () => { ranProtectedWork = true; });
+      } catch (error) {
+        failure = error;
+      }
+
+      expect(failure).toBeInstanceOf(PublicEvidenceValidationError);
+      expect((failure as PublicEvidenceValidationError).code).toBe("community_cache_busy");
+      expect(ranProtectedWork).toBe(false);
+      expect(readFileSync(join(lockPath, "owner.json"))).toEqual(ownerBefore);
+      const lockAfter = lstatSync(lockPath);
+      expect([lockAfter.dev, lockAfter.ino]).toEqual([lockBefore.dev, lockBefore.ino]);
+      expect(ownerCheck).toHaveBeenCalledTimes(1);
+      expect(ownerCheck).toHaveBeenCalledWith(process.pid, 0);
+    } finally {
+      ownerCheck.mockRestore();
     }
-
-    const elapsedMs = performance.now() - startedAt;
-    expect(failure).toBeInstanceOf(PublicEvidenceValidationError);
-    expect((failure as PublicEvidenceValidationError).code).toBe("community_cache_busy");
-    expect(elapsedMs).toBeLessThan(500);
-    expect(existsSync(lockPath)).toBe(true);
   });
 
   test("a competing reclaim claim prevents a second stale reclaimer from deleting the lock", () => {
diff --git a/tests/lab/lab-public-surfaces.test.ts b/tests/lab/lab-public-surfaces.test.ts
index e28d601a2c..bf798e2992 100644
--- a/tests/lab/lab-public-surfaces.test.ts
+++ b/tests/lab/lab-public-surfaces.test.ts
@@ -1,5 +1,5 @@
 import { afterEach, describe, expect, test } from "bun:test";
-import { existsSync, mkdirSync, readFileSync, readdirSync, writeFileSync } from "node:fs";
+import { existsSync, lstatSync, mkdirSync, readFileSync, readdirSync, writeFileSync } from "node:fs";
 import { tmpdir } from "node:os";
 import { join } from "node:path";
 import { handleLabCommand } from "../../src/cli/lab";
@@ -286,7 +286,7 @@ describe("CL-10 management local public evidence", () => {
     }
   });
 
-  test("busy community lock is a prompt retryable service response", async () => {
+  test("busy community lock returns a retryable service response and preserves ownership", async () => {
     const home = tempHome();
     const lockPath = join(labCommunityDir(home), ".mutation-lock");
     mkdirSync(lockPath, { recursive: true, mode: 0o700 });
@@ -300,16 +300,18 @@ describe("CL-10 management local public evidence", () => {
       { encoding: "utf8", mode: 0o600 },
     );
 
-    const startedAt = performance.now();
+    const lockBefore = lstatSync(lockPath);
+    const ownerBefore = readFileSync(join(lockPath, "owner.json"));
     const response = await api(home, "/api/lab/public/community");
-    const elapsedMs = performance.now() - startedAt;
 
-    expect(elapsedMs).toBeLessThan(500);
     expect(response.status).toBe(503);
     expect(response.headers.get("retry-after")).toBe("1");
     expect(await response.json()).toMatchObject({
       error: { code: "community_cache_busy" },
     });
+    expect(readFileSync(join(lockPath, "owner.json"))).toEqual(ownerBefore);
+    const lockAfter = lstatSync(lockPath);
+    expect([lockAfter.dev, lockAfter.ino]).toEqual([lockBefore.dev, lockBefore.ino]);
   });
 
   test("does not expose a remote publish endpoint", async () => {