fix: Discover before server call, preserve caller precedence

- Move Discover BEFORE HttpDownloadSource construction so the server
  call sees real manifest values, not placeholder defaults.
- Discover only fills empty context fields — caller-provided values
  take precedence over manifest (matches old ?? behaviour).

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

Author: JusterZhu

src/c#/GeneralUpdate.Core/Configuration/AppMetadataDiscoverer.cs

@@ -25,19 +25,20 @@ public static void Discover(UpdateContext context)
 
         if (manifest == null) return;
 
-        if (!string.IsNullOrWhiteSpace(manifest.MainAppName))
+        // Only fill empty fields — caller-provided values take precedence.
+        if (string.IsNullOrWhiteSpace(context.MainAppName) && !string.IsNullOrWhiteSpace(manifest.MainAppName))
             context.MainAppName = manifest.MainAppName;
-        if (!string.IsNullOrWhiteSpace(manifest.UpdateAppName))
+        if (string.IsNullOrWhiteSpace(context.UpdateAppName) && !string.IsNullOrWhiteSpace(manifest.UpdateAppName))
             context.UpdateAppName = manifest.UpdateAppName;
-        if (!string.IsNullOrWhiteSpace(manifest.ClientVersion))
+        if (string.IsNullOrWhiteSpace(context.ClientVersion) && !string.IsNullOrWhiteSpace(manifest.ClientVersion))
             context.ClientVersion = manifest.ClientVersion;
-        if (!string.IsNullOrWhiteSpace(manifest.UpgradeClientVersion))
+        if (string.IsNullOrWhiteSpace(context.UpgradeClientVersion) && !string.IsNullOrWhiteSpace(manifest.UpgradeClientVersion))
             context.UpgradeClientVersion = manifest.UpgradeClientVersion;
-        if (!string.IsNullOrWhiteSpace(manifest.ProductId))
+        if (string.IsNullOrWhiteSpace(context.ProductId) && !string.IsNullOrWhiteSpace(manifest.ProductId))
             context.ProductId = manifest.ProductId;
-        if (!string.IsNullOrWhiteSpace(manifest.UpdatePath))
+        if (string.IsNullOrWhiteSpace(context.UpdatePath) && !string.IsNullOrWhiteSpace(manifest.UpdatePath))
             context.UpdatePath = manifest.UpdatePath;
-        if (!string.IsNullOrWhiteSpace(manifest.AppType)
+        if (context.AppType == null && !string.IsNullOrWhiteSpace(manifest.AppType)
             && Enum.TryParse<AppType>(manifest.AppType, out var at))
             context.AppType = at;
     }

src/c#/GeneralUpdate.Core/Strategy/ClientStrategy.cs

@@ -398,6 +398,14 @@ private async Task ExecuteStandardWorkflowAsync()
         GeneralTracer.Info(
             $"ClientStrategy: validating client={_configInfo!.ClientVersion}, upgrade={_configInfo.UpgradeClientVersion}");
 
+        // Discover identity metadata from the manifest in InstallPath BEFORE
+        // constructing HttpDownloadSource so the server call sees real values.
+        // UpdateStrategy writes versions back to InstallPath after each update;
+        // using the parameterless Load() would read from BaseDirectory instead
+        // and could pick up a stale manifest when InstallPath is customized.
+        // Only fills empty fields — caller-provided values take precedence.
+        AppMetadataDiscoverer.Discover(_configInfo!);
+
         // Use injected DownloadSource (Hub/HTTP), or default to HttpDownloadSource
         var downloadSource = DownloadSource ?? new Download.Sources.HttpDownloadSource(
             _configInfo.UpdateUrl,
@@ -412,12 +420,6 @@ private async Task ExecuteStandardWorkflowAsync()
         // Call server validation — returns assets from the two Validate calls
         var sourceResult = await downloadSource.ListAsync().ConfigureAwait(false);
 
-        // Discover identity metadata from the manifest in InstallPath.
-        // UpdateStrategy writes versions back to InstallPath after each update;
-        // using the parameterless Load() would read from BaseDirectory instead
-        // and could pick up a stale manifest when InstallPath is customized.
-        // Caller's explicit value takes precedence; manifest is a fallback.
-        AppMetadataDiscoverer.Discover(_configInfo!);
         var localClientVersion = _configInfo!.ClientVersion;
         var localUpgradeVersion = _configInfo.UpgradeClientVersion ?? localClientVersion;