Add closed_at timestamp tracking to issues

- Add closed_at field to Issue type with JSON marshaling
- Implement closed_at timestamp in SQLite storage layer
- Update import/export to handle closed_at field
- Add comprehensive tests for closed_at functionality
- Maintain backward compatibility with existing databases

Amp-Thread-ID: https://ampcode.com/threads/T-f3a7799b-f91e-4432-a690-aae0aed364b3
Co-authored-by: Amp <amp@ampcode.com>

internal/types/types.go

@@ -46,6 +46,13 @@ func (i *Issue) Validate() error {
 	if i.EstimatedMinutes != nil && *i.EstimatedMinutes < 0 {
 		return fmt.Errorf("estimated_minutes cannot be negative")
 	}
+	// Enforce closed_at invariant: closed_at should be set if and only if status is closed
+	if i.Status == StatusClosed && i.ClosedAt == nil {
+		return fmt.Errorf("closed issues must have closed_at timestamp")
+	}
+	if i.Status != StatusClosed && i.ClosedAt != nil {
+		return fmt.Errorf("non-closed issues cannot have closed_at timestamp")
+	}
 	return nil
 }
 

internal/types/types_test.go

@@ -120,6 +120,57 @@ func TestIssueValidation(t *testing.T) {
 			},
 			wantErr: false,
 		},
+		{
+			name: "closed issue without closed_at",
+			issue: Issue{
+				ID:        "test-1",
+				Title:     "Test",
+				Status:    StatusClosed,
+				Priority:  2,
+				IssueType: TypeFeature,
+				ClosedAt:  nil,
+			},
+			wantErr: true,
+			errMsg:  "closed issues must have closed_at timestamp",
+		},
+		{
+			name: "open issue with closed_at",
+			issue: Issue{
+				ID:        "test-1",
+				Title:     "Test",
+				Status:    StatusOpen,
+				Priority:  2,
+				IssueType: TypeFeature,
+				ClosedAt:  timePtr(time.Now()),
+			},
+			wantErr: true,
+			errMsg:  "non-closed issues cannot have closed_at timestamp",
+		},
+		{
+			name: "in_progress issue with closed_at",
+			issue: Issue{
+				ID:        "test-1",
+				Title:     "Test",
+				Status:    StatusInProgress,
+				Priority:  2,
+				IssueType: TypeFeature,
+				ClosedAt:  timePtr(time.Now()),
+			},
+			wantErr: true,
+			errMsg:  "non-closed issues cannot have closed_at timestamp",
+		},
+		{
+			name: "closed issue with closed_at",
+			issue: Issue{
+				ID:        "test-1",
+				Title:     "Test",
+				Status:    StatusClosed,
+				Priority:  2,
+				IssueType: TypeFeature,
+				ClosedAt:  timePtr(time.Now()),
+			},
+			wantErr: false,
+		},
 	}
 
 	for _, tt := range tests {
@@ -287,6 +338,10 @@ func intPtr(i int) *int {
 	return &i
 }
 
+func timePtr(t time.Time) *time.Time {
+	return &t
+}
+
 func contains(s, substr string) bool {
 	return len(s) >= len(substr) && (s == substr || len(s) > len(substr) && (s[:len(substr)] == substr || s[len(s)-len(substr):] == substr || containsMiddle(s, substr)))
 }