diff --git a/cmd/verstak-gui/bindings_plugins.go b/cmd/verstak-gui/bindings_plugins.go
index 31b1286..56c28bf 100644
--- a/cmd/verstak-gui/bindings_plugins.go
+++ b/cmd/verstak-gui/bindings_plugins.go
@@ -115,14 +115,16 @@ func (a *App) SetPluginEnabled(name string, enabled bool) error {
 		}
 		// Activate runtime — if this fails, do NOT persist to config
 		if err := a.plugins.ActivatePlugin(name); err != nil {
-			// Rollback: deactivate and un-enable
+			// Rollback: deactivate runtime AND un-enable in-memory state
 			a.plugins.DeactivatePlugin(name)
+			a.plugins.Disable(name)
 			return fmt.Errorf("activate %q: %w", name, err)
 		}
 		// Only persist to config after successful activation
 		if err := a.saveEnabledPlugin(name); err != nil {
 			// Config save failed — rollback runtime too
 			a.plugins.DeactivatePlugin(name)
+			a.plugins.Disable(name)
 			return fmt.Errorf("save config for %q: %w", name, err)
 		}
 	} else {
diff --git a/cmd/verstak-gui/plugins_lifecycle_test.go b/cmd/verstak-gui/plugins_lifecycle_test.go
new file mode 100644
index 0000000..a41775b
--- /dev/null
+++ b/cmd/verstak-gui/plugins_lifecycle_test.go
@@ -0,0 +1,123 @@
+package main
+
+import (
+	"os"
+	"path/filepath"
+	"testing"
+
+	"verstak/internal/core/config"
+	"verstak/internal/core/plugins"
+)
+
+// TestSetPluginEnabled_BrokenPlugin_Rollback verifies that when activation fails,
+// the plugin is fully rolled back: not Active, not Enabled, and not in config.
+func TestSetPluginEnabled_BrokenPlugin_Rollback(t *testing.T) {
+	// Isolate global config to a temp dir so we don't pollute the user's real config
+	tmpCfgDir := filepath.Join(t.TempDir(), "config")
+	if err := os.MkdirAll(tmpCfgDir, 0o750); err != nil {
+		t.Fatalf("mkdir config dir: %v", err)
+	}
+	t.Setenv("XDG_CONFIG_HOME", tmpCfgDir)
+
+	vaultRoot := t.TempDir()
+
+	// Create .verstak/plugins/ structure
+	pluginsDir := filepath.Join(vaultRoot, ".verstak", "plugins")
+	if err := os.MkdirAll(pluginsDir, 0o750); err != nil {
+		t.Fatalf("mkdir plugins: %v", err)
+	}
+
+	// Create a broken plugin: valid Lua but invalid background task interval
+	brokenDir := filepath.Join(pluginsDir, "broken")
+	if err := os.MkdirAll(brokenDir, 0o750); err != nil {
+		t.Fatalf("mkdir broken plugin: %v", err)
+	}
+
+	// plugin.json with an invalid background task interval ("not-a-duration")
+	pluginJSON := `{
+		"name": "broken",
+		"version": "0.1.0",
+		"hooks": {
+			"on_install": "on_install",
+			"on_init": "on_init"
+		},
+		"background_tasks": [
+			{"id": "bad-task", "interval": "not-a-duration", "script": "bad.lua"}
+		]
+	}`
+	if err := os.WriteFile(filepath.Join(brokenDir, "plugin.json"), []byte(pluginJSON), 0o644); err != nil {
+		t.Fatalf("write plugin.json: %v", err)
+	}
+
+	// main.lua — on_install is a no-op (tables not needed for this test),
+	// on_init is harmless. Activation will fail on the invalid background task interval.
+	mainLua := `
+function on_install()
+	-- no-op
+end
+
+function on_init()
+	-- harmless
+end
+`
+	if err := os.WriteFile(filepath.Join(brokenDir, "main.lua"), []byte(mainLua), 0o644); err != nil {
+		t.Fatalf("write main.lua: %v", err)
+	}
+
+	// Create App with real plugin manager
+	app := &App{
+		plugins:   plugins.NewManager(vaultRoot),
+		vault:     vaultRoot,
+		vaultOpen: true,
+	}
+
+	// Discover the plugin
+	app.plugins.Discover()
+
+	// Step 1: Install the plugin (creates tables, marks installed in config)
+	if err := app.plugins.Install("broken"); err != nil {
+		t.Fatalf("install broken plugin: %v", err)
+	}
+
+	// Verify plugin is installed
+	if !app.plugins.IsInstalled("broken") {
+		t.Fatal("expected plugin to be installed")
+	}
+
+	// Step 2: Try to enable — should fail because background task has invalid interval
+	err := app.SetPluginEnabled("broken", true)
+	if err == nil {
+		t.Fatal("expected SetPluginEnabled to fail for broken plugin, got nil")
+	}
+	t.Logf("SetPluginEnabled returned expected error: %v", err)
+
+	// Step 3: Verify plugin is NOT Active and NOT Enabled (in-memory rollback)
+	found := false
+	for _, p := range app.plugins.Plugins() {
+		if p.Meta.Name == "broken" {
+			found = true
+			if p.Active {
+				t.Error("expected plugin to NOT be Active after failed activation")
+			}
+			if p.Enabled {
+				t.Error("expected plugin to NOT be Enabled after failed activation (in-memory rollback)")
+			}
+		}
+	}
+	if !found {
+		t.Fatal("plugin 'broken' not found in manager")
+	}
+
+	// Step 4: Verify plugin is NOT in EnabledPlugins config
+	appCfg, err := config.LoadAppConfig()
+	if err != nil {
+		t.Fatalf("load app config: %v", err)
+	}
+	if appCfg != nil {
+		for _, name := range appCfg.EnabledPlugins {
+			if name == "broken" {
+				t.Error("expected 'broken' to NOT be in EnabledPlugins config after failed activation")
+			}
+		}
+	}
+}
diff --git a/internal/core/plugins/manager_lifecycle.go b/internal/core/plugins/manager_lifecycle.go
index bef96cf..e0f887e 100644
--- a/internal/core/plugins/manager_lifecycle.go
+++ b/internal/core/plugins/manager_lifecycle.go
@@ -12,6 +12,7 @@ import (
 // ActivatePlugin fully activates a plugin: creates Lua VM, loads main.lua, starts scheduler.
 // Only works if plugin is installed and enabled but not yet active.
 // Returns error if VM creation, script loading, scheduler setup, or on_init hook fails.
+// on_init failure is fatal — the plugin cannot run without proper initialization.
 func (m *Manager) ActivatePlugin(name string) error {
 	for i := range m.plugins {
 		p := &m.plugins[i]
@@ -56,8 +57,12 @@ func (m *Manager) ActivatePlugin(name string) error {
 
 		if hookName, ok := p.Meta.Hooks["on_init"]; ok {
 			if err := vm.CallHook(hookName); err != nil {
-				// on_init failure is non-fatal for activation — log but continue
-				log.Printf("[plugins] %s: on_init error: %v", name, err)
+				// on_init failure is fatal — rollback activation
+				p.scheduler.Stop()
+				p.scheduler = nil
+				p.vm.Close()
+				p.vm = nil
+				return fmt.Errorf("on_init for %q: %w", name, err)
 			}
 		}