fix(update): compare preview installs to stable

Author: luvs01

src/update/notify.ts

@@ -92,7 +92,7 @@ function gt(a: number[], b: number[]): boolean {
 export function isNewer(latest: string, current: string, channel: Channel): boolean {
   if (channel === "latest") {
     const l = parseStable(latest);
-    const c = parseStable(current);
+    const c = parseStable(current) ?? parsePreview(current)?.slice(0, 3);
     if (!l || !c) return false;
     return gt(l, c);
   }

tests/update-job.test.ts

@@ -85,6 +85,24 @@ describe("GUI update check", () => {
     expect(result.canUpdate).toBe(false);
     expect(result.reason).toBe("already_latest");
   });
+
+  test("offers a stable update from an older preview but not the same base", () => {
+    const olderPreview = checkForUpdate("latest", {
+      currentVersion: () => "2.8.2-preview.20260731",
+      detectInstall: () => "npm",
+      latestVersion: () => "2.9.1",
+    });
+    expect(olderPreview.updateAvailable).toBe(true);
+    expect(olderPreview.canUpdate).toBe(true);
+
+    const sameBasePreview = checkForUpdate("latest", {
+      currentVersion: () => "2.9.1-preview.20260731",
+      detectInstall: () => "npm",
+      latestVersion: () => "2.9.1",
+    });
+    expect(sameBasePreview.updateAvailable).toBe(false);
+    expect(sameBasePreview.canUpdate).toBe(false);
+  });
 });
 
 describe("GUI update execution decisions", () => {

tests/update-notify.test.ts

@@ -38,6 +38,10 @@ describe("isNewer — latest channel", () => {
   test("prereleases are ignored on the stable channel", () => {
     expect(isNewer("2.7.0-preview.1", "2.6.4", "latest")).toBe(false);
   });
+  test("stable releases compare against a preview current by its base version", () => {
+    expect(isNewer("2.9.1", "2.8.2-preview.20260731", "latest")).toBe(true);
+    expect(isNewer("2.9.1", "2.9.1-preview.20260731", "latest")).toBe(false);
+  });
 });
 
 describe("isNewer — preview channel", () => {