Persist undo/redo history across runs with a 20-entry cap.

Serialize create/update/delete commands to DataDir/history.json and reload them on startup via OpenHistory.

Co-authored-by: Cursor <cursoragent@cursor.com>

internal/command/persist_test.go

@@ -0,0 +1,80 @@
+package command_test
+
+import (
+	"os"
+	"path/filepath"
+	"testing"
+
+	"task/internal/command"
+	"task/internal/ticket"
+)
+
+func TestHistoryPersistsAcrossOpen(t *testing.T) {
+	dir := t.TempDir()
+	store := ticket.NewJSONStore(dir)
+	path := command.HistoryPath(dir)
+
+	h1, err := command.OpenHistory(path, store)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if err := h1.Do(&command.CreateTicket{
+		Store: store,
+		Ticket: ticket.Ticket{
+			Title: "Persist me", ProjectID: "inbox", Status: ticket.StatusTodo,
+		},
+	}); err != nil {
+		t.Fatal(err)
+	}
+	if _, err := os.Stat(path); err != nil {
+		t.Fatalf("history file missing: %v", err)
+	}
+
+	h2, err := command.OpenHistory(path, store)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if !h2.CanUndo() {
+		t.Fatal("expected undo after reload")
+	}
+	if err := h2.Undo(); err != nil {
+		t.Fatal(err)
+	}
+	list, err := store.List("inbox")
+	if err != nil || len(list) != 0 {
+		t.Fatalf("after persistent undo: %v len=%d", err, len(list))
+	}
+}
+
+func TestHistoryCapsAtMax(t *testing.T) {
+	dir := t.TempDir()
+	store := ticket.NewJSONStore(dir)
+	h, err := command.OpenHistory(filepath.Join(dir, "history.json"), store)
+	if err != nil {
+		t.Fatal(err)
+	}
+	for i := 0; i < command.MaxHistory+5; i++ {
+		if err := h.Do(&command.CreateTicket{
+			Store: store,
+			Ticket: ticket.Ticket{
+				Title: "t", ProjectID: "inbox", Status: ticket.StatusTodo,
+			},
+		}); err != nil {
+			t.Fatal(err)
+		}
+	}
+	// Count undos available
+	n := 0
+	for h.CanUndo() {
+		if err := h.Undo(); err != nil {
+			t.Fatal(err)
+		}
+		n++
+		if n > command.MaxHistory+1 {
+			t.Fatal("undo stack larger than cap")
+		}
+	}
+	if n != command.MaxHistory {
+		t.Fatalf("undo count = %d, want %d", n, command.MaxHistory)
+	}
+}