Nil pointer dereference in OnConnectionConfigChanged closes #4784 (#4829)

* Add test demonstrating bug #4784 - OnConnectionConfigChanged panics with nil pool

🤖 Generated with [Claude Code](https://claude.com/claude-code)

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

* Fix #4784: Add nil pool check in handlePluginInstanceChanges

🤖 Generated with [Claude Code](https://claude.com/claude-code)

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

---------

Co-authored-by: Claude <noreply@anthropic.com>

pkg/pluginmanager_service/plugin_manager_plugin_instance.go

@@ -27,6 +27,12 @@ func (m *PluginManager) handlePluginInstanceChanges(ctx context.Context, newPlug
 	// update connectionConfigMap
 	m.plugins = newPlugins
 
+	// if pool is nil, we're in a test environment or the plugin manager hasn't been fully initialized
+	// in this case, we can't repopulate the plugin table, so just return early
+	if m.pool == nil {
+		return nil
+	}
+
 	// repopulate the plugin table
 	conn, err := m.pool.Acquire(ctx)
 	if err != nil {

pkg/pluginmanager_service/plugin_manager_test.go

@@ -1,6 +1,7 @@
 package pluginmanager_service
 
 import (
+	"context"
 	"fmt"
 	"runtime"
 	"sync"
@@ -714,3 +715,35 @@ func TestPluginManager_StressConcurrentMapAccess(t *testing.T) {
 	close(stopCh)
 	wg.Wait()
 }
+
+// Test 24: OnConnectionConfigChanged with Nil Pool (Bug #4784)
+
+// TestPluginManager_OnConnectionConfigChanged_EmptyToNonEmpty tests the scenario where
+// a PluginManager with no pool (e.g., in a testing environment) receives a configuration change.
+// This test demonstrates bug #4784 - a nil pointer panic when m.pool is nil.
+func TestPluginManager_OnConnectionConfigChanged_EmptyToNonEmpty(t *testing.T) {
+	// Create a minimal PluginManager without pool initialization
+	// This simulates a testing scenario or edge case where the pool might not be initialized
+	m := &PluginManager{
+		plugins: make(map[string]*plugin.Plugin),
+		// Note: pool is intentionally nil to demonstrate the bug
+	}
+
+	// Create a new plugin map with one plugin
+	newPlugins := map[string]*plugin.Plugin{
+		"aws": {
+			Plugin:   "hub.steampipe.io/plugins/turbot/aws@latest",
+			Instance: "aws",
+		},
+	}
+
+	ctx := context.Background()
+
+	// This should panic with nil pointer dereference when trying to use m.pool
+	err := m.handlePluginInstanceChanges(ctx, newPlugins)
+
+	// If we get here without panic, the fix is working
+	if err != nil {
+		t.Logf("Expected error when pool is nil: %v", err)
+	}
+}