feat(server): online session history with configurable stats window (#1243)

Add persisted online sessions, configurable retention and online history statistics with lifecycle, recovery, timezone and concurrency regression coverage.

Co-authored-by: naiba/CloudCode <hi+cloudcode@nai.ba>

cmd/dashboard/controller/setting_single_commit_test.go

@@ -0,0 +1,49 @@
+package controller
+
+import (
+	"go/ast"
+	"go/parser"
+	"go/token"
+	"testing"
+
+	"github.com/stretchr/testify/require"
+)
+
+// The transition helper owns Save (including unchanged MCP settings). A direct
+// second Save after it can fail after persistence and irreversible revocation.
+func TestUpdateConfigHasSinglePersistenceOwner(t *testing.T) {
+	file, err := parser.ParseFile(token.NewFileSet(), "setting.go", nil, 0)
+	require.NoError(t, err)
+	transitions, directSaves := 0, 0
+	found := false
+	for _, decl := range file.Decls {
+		fn, ok := decl.(*ast.FuncDecl)
+		if !ok || fn.Name.Name != "updateConfig" {
+			continue
+		}
+		found = true
+		ast.Inspect(fn.Body, func(n ast.Node) bool {
+			call, ok := n.(*ast.CallExpr)
+			if !ok {
+				return true
+			}
+			if ident, ok := call.Fun.(*ast.Ident); ok && ident.Name == "applyEnableMCPTransition" {
+				transitions++
+			}
+			if selector, ok := call.Fun.(*ast.SelectorExpr); ok && selector.Sel.Name == "Save" {
+				directSaves++
+			}
+			return true
+		})
+	}
+	require.True(t, found)
+	require.Equal(t, 1, transitions)
+	require.Zero(t, directSaves)
+}
+
+func TestUnchangedMCPTransitionStillSavesOnce(t *testing.T) {
+	saves := 0
+	err := applyEnableMCPTransition(true, true, func(bool) {}, func() error { saves++; return nil }, func() { t.Error("unchanged MCP must not revoke streams") })
+	require.NoError(t, err)
+	require.Equal(t, 1, saves)
+}