feat: persist server installation errors and show retry UI instead of auto-marking as handled

Author: msanatan

MCPForUnity/Editor/Helpers/PackageLifecycleManager.cs

@@ -14,6 +14,7 @@ public static class PackageLifecycleManager
     {
         private const string VersionKeyPrefix = "MCPForUnity.InstalledVersion:";
         private const string LegacyInstallFlagKey = "MCPForUnity.ServerInstalled"; // For migration
+        private const string InstallErrorKeyPrefix = "MCPForUnity.InstallError:"; // Stores last installation error
 
         static PackageLifecycleManager()
         {
@@ -83,17 +84,17 @@ private static void PerformInstallation(string version, string versionKey, bool
                 error = ex.Message;
                 capturedEx = ex;
 
-                // Mark as handled to avoid repeated failures
-                EditorPrefs.SetBool(versionKey, true);
-                if (isFirstTimeInstall)
-                {
-                    EditorPrefs.SetBool(LegacyInstallFlagKey, true);
-                }
+                // Store the error for display in the UI, but don't mark as handled
+                // This allows the user to manually rebuild via the "Rebuild Server" button
+                string errorKey = InstallErrorKeyPrefix + version;
+                EditorPrefs.SetString(errorKey, ex.Message ?? "Unknown error");
+                
+                // Don't mark as installed - user needs to manually rebuild
             }
 
             if (!string.IsNullOrEmpty(error))
             {
-                McpLog.Info($"Server check: {error}. Download via Window > MCP For Unity if needed.", always: false);
+                McpLog.Info($"Server installation failed: {error}. Use Window > MCP For Unity > Rebuild Server to retry.", always: false);
             }
         }
 
@@ -201,5 +202,41 @@ private static void CleanupLegacyPrefs()
             }
             catch { }
         }
+
+        /// <summary>
+        /// Gets the last installation error for the current package version, if any.
+        /// Returns null if there was no error or the error has been cleared.
+        /// </summary>
+        public static string GetLastInstallError()
+        {
+            try
+            {
+                string currentVersion = GetPackageVersion();
+                string errorKey = InstallErrorKeyPrefix + currentVersion;
+                if (EditorPrefs.HasKey(errorKey))
+                {
+                    return EditorPrefs.GetString(errorKey, null);
+                }
+            }
+            catch { }
+            return null;
+        }
+
+        /// <summary>
+        /// Clears the last installation error. Should be called after a successful manual rebuild.
+        /// </summary>
+        public static void ClearLastInstallError()
+        {
+            try
+            {
+                string currentVersion = GetPackageVersion();
+                string errorKey = InstallErrorKeyPrefix + currentVersion;
+                if (EditorPrefs.HasKey(errorKey))
+                {
+                    EditorPrefs.DeleteKey(errorKey);
+                }
+            }
+            catch { }
+        }
     }
 }

MCPForUnity/Editor/Helpers/ServerInstaller.cs

@@ -488,6 +488,10 @@ public static bool RebuildMcpServer()
                 }
 
                 McpLog.Info($"Server rebuilt successfully at {destRoot} (version {embeddedVer})");
+                
+                // Clear any previous installation error
+                PackageLifecycleManager.ClearLastInstallError();
+                
                 return true;
             }
             catch (Exception ex)

MCPForUnity/Editor/Windows/MCPForUnityEditorWindow.cs

@@ -641,8 +641,15 @@ private void UpdateServerStatusBanner()
                 rebuildServerButton.style.display = DisplayStyle.None;
             }
 
+            // Check for installation errors first
+            string installError = PackageLifecycleManager.GetLastInstallError();
+            if (!string.IsNullOrEmpty(installError))
+            {
+                serverStatusMessage.text = $"\u274C Server installation failed: {installError}. Click 'Rebuild Server' to retry.";
+                serverStatusBanner.style.display = DisplayStyle.Flex;
+            }
             // Update banner
-            if (!hasEmbedded && string.IsNullOrEmpty(installedVer))
+            else if (!hasEmbedded && string.IsNullOrEmpty(installedVer))
             {
                 serverStatusMessage.text = "\u26A0 Server not installed. Click 'Download & Install Server' to get started.";
                 serverStatusBanner.style.display = DisplayStyle.Flex;