fix: keep default release when latest has no compatible SKU artifact

After the getDefaultRelease SKU-compat fix, the default path was
graceful but the rollout-upgrade path stayed strict: if a device was in
the rollout bucket and the latest release lacked a compatible artifact
for the requested SKU, dbReleaseToMetadata still threw and 404'd the
whole request — even though responseJson already held a valid default.

Short-circuit the upgrade when the latest release has no compatible
artifact and update the regression test to assert the default is kept
instead of asserting the throw.

src/releases.ts

@@ -617,26 +617,30 @@ export async function Retrieve(req: Request, res: Response) {
 
   // Background update checks follow rollout percentages so new releases roll
   // out gradually. Devices outside the bucket fall back to the default (the
-  // newest 100%-rolled-out release).
+  // newest 100%-rolled-out release). If the latest release lacks a compatible
+  // artifact for this SKU (e.g. a SKU-specific build hasn't shipped yet) we
+  // silently keep the default rather than 404 the whole request.
   const responseJson = toRelease(
     dbReleaseToMetadata(defaultAppRelease, query.sku),
     dbReleaseToMetadata(defaultSystemRelease, query.sku),
   );
 
   if (
-    await isDeviceEligibleForLatestRelease(
+    latestAppRelease.artifacts.length > 0 &&
+    (await isDeviceEligibleForLatestRelease(
       latestAppRelease.rolloutPercentage,
       query.deviceId,
-    )
+    ))
   ) {
     setAppRelease(responseJson, dbReleaseToMetadata(latestAppRelease, query.sku));
   }
 
   if (
-    await isDeviceEligibleForLatestRelease(
+    latestSystemRelease.artifacts.length > 0 &&
+    (await isDeviceEligibleForLatestRelease(
       latestSystemRelease.rolloutPercentage,
       query.deviceId,
-    )
+    ))
   ) {
     setSystemRelease(responseJson, dbReleaseToMetadata(latestSystemRelease, query.sku));
   }

test/releases.test.ts

@@ -489,7 +489,7 @@ describe("Retrieve handler", () => {
       });
     });
 
-    it("does not fall back when the latest release lacks a compatible artifact", async () => {
+    it("keeps the default when the latest release lacks a compatible artifact for an in-bucket device", async () => {
       await createDbRelease("app", "3.3.0", 100, [
         {
           ...releaseArtifact("app", "3.3.0", DEFAULT_SKU),
@@ -506,19 +506,28 @@ describe("Retrieve handler", () => {
         releaseArtifact("system", "3.3.0", DEFAULT_SKU, "system-default-hash"),
         releaseArtifact("system", "3.3.0", SDMMC_SKU, "system-sdmmc-hash"),
       ]);
+      // system 3.3.1 ships only with the default-SKU artifact — no sdmmc binary.
       await createDbRelease("system", "3.3.1", 100);
 
-      await expect(
-        Retrieve(
-          createMockRequest({
-            deviceId: "sdmmc-compatible-fallback-device",
-            sku: SDMMC_SKU,
-          }),
-          createMockResponse(),
-        ),
-      ).rejects.toThrow(
-        'Version 3.3.1 predates SKU support and cannot serve SKU "jetkvm-v2-sdmmc"',
+      // Every device is in-bucket at 100% rollout, so this exercises the
+      // upgrade path. The request must keep the default 3.3.0 system release
+      // rather than 404 because 3.3.1 has no sdmmc binary.
+      const res = createMockResponse();
+      await Retrieve(
+        createMockRequest({
+          deviceId: "sdmmc-compatible-fallback-device",
+          sku: SDMMC_SKU,
+        }),
+        res,
       );
+
+      expect(jsonBody(res)).toMatchObject({
+        appVersion: "3.3.1",
+        appUrl: artifactUrl("app", "3.3.1"),
+        systemVersion: "3.3.0",
+        systemUrl: artifactUrl("system", "3.3.0", SDMMC_SKU),
+        systemHash: "system-sdmmc-hash",
+      });
     });
 
     it("does not discover or create stable releases from S3", async () => {