diff --git a/.github/workflows/desktop-release.yml b/.github/workflows/desktop-release.yml
index 25d7ffd23..792fbacf5 100644
--- a/.github/workflows/desktop-release.yml
+++ b/.github/workflows/desktop-release.yml
@@ -446,4 +446,25 @@ jobs:
           fi
           timestamp="$(date -u +"%Y-%m-%dT%H:%M:%S.000Z")"
           node ../scripts/stamp-rollout.mjs --release-date "$timestamp" --rollout-hours "$ROLLOUT_HOURS" "${files[@]}"
+          ROLLOUT_HOURS_EXPECTED="$ROLLOUT_HOURS" RELEASE_DATE_EXPECTED="$timestamp" node -e '
+            const yaml = require("js-yaml");
+            const fs = require("fs");
+            const expectedHours = Number(process.env.ROLLOUT_HOURS_EXPECTED);
+            const expectedDate = process.env.RELEASE_DATE_EXPECTED;
+            if (!Number.isFinite(expectedHours) || expectedHours < 0) {
+              throw new Error(`expected non-negative rolloutHours, got ${process.env.ROLLOUT_HOURS_EXPECTED}`);
+            }
+            for (const f of process.argv.slice(1)) {
+              const m = yaml.load(fs.readFileSync(f, "utf8")) ?? {};
+              if (m.rolloutHours !== expectedHours) {
+                throw new Error(`${f}: rolloutHours=${m.rolloutHours}, expected ${expectedHours}`);
+              }
+              if (m.releaseDate !== expectedDate) {
+                throw new Error(`${f}: releaseDate=${m.releaseDate}, expected ${expectedDate}`);
+              }
+              if (typeof m.version !== "string" || m.version.length === 0) {
+                throw new Error(`${f}: missing or invalid version`);
+              }
+            }
+          ' "${files[@]}"
           gh release upload "$RELEASE_TAG" "${files[@]}" --clobber --repo "${{ github.repository }}"
diff --git a/packages/desktop/src/features/auto-updater.test.ts b/packages/desktop/src/features/auto-updater.test.ts
index b8d8f122f..f810b8da3 100644
--- a/packages/desktop/src/features/auto-updater.test.ts
+++ b/packages/desktop/src/features/auto-updater.test.ts
@@ -14,7 +14,12 @@ vi.mock("electron-updater", () => ({
   autoUpdater: {},
 }));
 
-import { resolveStagingUserId, rolloutManifestSchema, shouldAdmitToRollout } from "./auto-updater";
+import {
+  bucketFromStagingUserId,
+  resolveStagingUserId,
+  rolloutManifestSchema,
+  shouldAdmitToRollout,
+} from "./auto-updater";
 
 describe("shouldAdmitToRollout", () => {
   it("admits beta, missing rollout hours, zero-hour rollout, and missing release date", () => {
@@ -86,6 +91,61 @@ describe("shouldAdmitToRollout", () => {
     ).toBe(false);
   });
 
+  it("blocks the bucket-zero client at exact release time, admits as soon as time advances", () => {
+    expect(
+      shouldAdmitToRollout({
+        channel: "stable",
+        rolloutHours: 24,
+        releaseDate: "2026-04-28T00:00:00.000Z",
+        now: Date.parse("2026-04-28T00:00:00.000Z"),
+        bucket: 0,
+      }),
+    ).toBe(false);
+    expect(
+      shouldAdmitToRollout({
+        channel: "stable",
+        rolloutHours: 24,
+        releaseDate: "2026-04-28T00:00:00.000Z",
+        now: Date.parse("2026-04-28T00:00:00.001Z"),
+        bucket: 0,
+      }),
+    ).toBe(true);
+  });
+
+  it("admits the highest-bucket client at and past the rollout end", () => {
+    const maxBucket = (0x100000000 - 1) / 0x100000000;
+    expect(
+      shouldAdmitToRollout({
+        channel: "stable",
+        rolloutHours: 24,
+        releaseDate: "2026-04-28T00:00:00.000Z",
+        now: Date.parse("2026-04-29T00:00:00.000Z"),
+        bucket: maxBucket,
+      }),
+    ).toBe(true);
+    expect(
+      shouldAdmitToRollout({
+        channel: "stable",
+        rolloutHours: 24,
+        releaseDate: "2026-04-28T00:00:00.000Z",
+        now: Date.parse("2027-04-28T00:00:00.000Z"),
+        bucket: maxBucket,
+      }),
+    ).toBe(true);
+  });
+
+  it("admits when releaseDate is unparseable", () => {
+    expect(
+      shouldAdmitToRollout({
+        channel: "stable",
+        rolloutHours: 24,
+        releaseDate: "not a date",
+        now: Date.parse("2026-04-28T12:00:00.000Z"),
+        bucket: 0.99,
+      }),
+    ).toBe(true);
+  });
+
   it("treats garbage manifest rollout fields as missing and admits", () => {
     const parsed = rolloutManifestSchema.parse({
       rolloutHours: "not a number",
@@ -103,6 +163,14 @@ describe("shouldAdmitToRollout", () => {
     ).toBe(true);
   });
 
+  it("maps the maximum 32-bit slot to a bucket strictly less than 1", () => {
+    const allOnes = "ffffffff-ffff-ffff-ffff-ffffffffffff";
+    const allZeros = "00000000-0000-0000-0000-000000000000";
+    expect(bucketFromStagingUserId(allOnes)).toBeLessThan(1);
+    expect(bucketFromStagingUserId(allOnes)).toBeGreaterThan(0.999);
+    expect(bucketFromStagingUserId(allZeros)).toBe(0);
+  });
+
   it("creates and then reuses the on-disk staging user id", async () => {
     const tempDir = await mkdtemp(path.join(os.tmpdir(), "paseo-updater-id-"));
     const filePath = path.join(tempDir, ".updaterId");
diff --git a/packages/desktop/src/features/auto-updater.ts b/packages/desktop/src/features/auto-updater.ts
index f68867836..78949721f 100644
--- a/packages/desktop/src/features/auto-updater.ts
+++ b/packages/desktop/src/features/auto-updater.ts
@@ -69,8 +69,8 @@ export function shouldAdmitToRollout(args: {
   return args.bucket * 100 < pct;
 }
 
-function bucketFromStagingUserId(stagingUserId: string): number {
-  return UUID.parse(stagingUserId).readUInt32BE(12) / 0xffffffff;
+export function bucketFromStagingUserId(stagingUserId: string): number {
+  return UUID.parse(stagingUserId).readUInt32BE(12) / 0x100000000;
 }
 
 export async function resolveStagingUserId(filePath: string): Promise<string> {