feat(desktop): show what's changed in auto-update prompt

Publish HEALTHCHAT_CHANGES.md release notes into the update feeds so users
see what changed. macOS gets them natively via releases.json's notes field;
Windows fetches a published notes.txt, since Squirrel.Windows only delivers
releaseName through the update-downloaded event.

apps/desktop/src/updater.ts

@@ -78,6 +78,7 @@ export async function start(updateBaseUrl: string): Promise<void> {
     if (!updateBaseUrl.endsWith("/")) {
         updateBaseUrl = updateBaseUrl + "/";
     }
+    updateFeedBaseUrl = updateBaseUrl;
 
     try {
         let url: string;
@@ -184,6 +185,27 @@ interface ICachedUpdate {
     updateURL: string;
 }
 
+// The feed base URL passed to start(), retained so the update-downloaded handler can fetch
+// release notes out-of-band on Windows (see below).
+let updateFeedBaseUrl: string | undefined;
+
+// On Windows the autoUpdater never provides release notes: "With Squirrel.Windows only
+// releaseName is available" (https://www.electronjs.org/docs/latest/api/auto-updater). We
+// publish a notes.txt alongside the per-arch Squirrel feed and fetch it here so the renderer's
+// update toast can show "what's changed" the same way it does on macOS (where Squirrel.Mac
+// carries the notes natively via releases.json).
+async function fetchWindowsReleaseNotes(): Promise<string> {
+    if (process.platform !== "win32" || !updateFeedBaseUrl) return "";
+    try {
+        const res = await fetch(`${updateFeedBaseUrl}win32/${process.arch}/notes.txt`);
+        if (!res.ok) return "";
+        return await res.text();
+    } catch (err) {
+        console.log("Couldn't fetch Windows release notes", err);
+        return "";
+    }
+}
+
 // cache the latest update which has been downloaded as electron offers no api to read it
 let latestUpdateDownloaded: ICachedUpdate | undefined;
 autoUpdater
@@ -205,7 +227,13 @@ autoUpdater
     });
 
 autoUpdater.on("update-downloaded", (ev, releaseNotes, releaseName, releaseDate, updateURL) => {
-    // forward to renderer
-    latestUpdateDownloaded = { releaseNotes, releaseName, releaseDate, updateURL };
-    global.mainWindow?.webContents.send("update-downloaded", latestUpdateDownloaded);
+    void (async (): Promise<void> => {
+        // Windows delivers no release notes via the event, so fetch them out-of-band.
+        if (!releaseNotes) {
+            releaseNotes = await fetchWindowsReleaseNotes();
+        }
+        // forward to renderer
+        latestUpdateDownloaded = { releaseNotes, releaseName, releaseDate, updateURL };
+        global.mainWindow?.webContents.send("update-downloaded", latestUpdateDownloaded);
+    })();
 });