Harden issueDataChanged with type-safe comparisons

Based on code review feedback:
- Remove unsafe type assertions that could panic
- Add robust type conversion helpers (strFrom, intFrom, equalStatus, equalIssueType)
- Support multiple numeric types for priority (int, int32, int64, float64)
- Treat empty string and nil as equal for optional fields
- Add default case to detect unknown fields (conservative)
- Add comprehensive unit tests for all edge cases
- Test coverage: enums as strings, numeric conversions, nil/empty handling

Amp-Thread-ID: https://ampcode.com/threads/T-225f8c56-0710-46e9-9db2-dbf90cf91911
Co-authored-by: Amp <amp@ampcode.com>

cmd/bd/import_idempotent_test.go

@@ -12,6 +12,210 @@ import (
 	"github.com/steveyegge/beads/internal/types"
 )
 
+// TestIssueDataChanged tests the issueDataChanged helper function
+func TestIssueDataChanged(t *testing.T) {
+	tests := []struct {
+		name     string
+		existing *types.Issue
+		updates  map[string]interface{}
+		want     bool // true if changed, false if unchanged
+	}{
+		{
+			name: "no changes",
+			existing: &types.Issue{
+				Title:       "Test",
+				Description: "Desc",
+				Status:      types.StatusOpen,
+				Priority:    2,
+				IssueType:   types.TypeTask,
+			},
+			updates: map[string]interface{}{
+				"title":       "Test",
+				"description": "Desc",
+				"status":      types.StatusOpen,
+				"priority":    2,
+				"issue_type":  types.TypeTask,
+			},
+			want: false,
+		},
+		{
+			name: "title changed",
+			existing: &types.Issue{
+				Title: "Old Title",
+			},
+			updates: map[string]interface{}{
+				"title": "New Title",
+			},
+			want: true,
+		},
+		{
+			name: "status as string vs enum - unchanged",
+			existing: &types.Issue{
+				Status: types.StatusOpen,
+			},
+			updates: map[string]interface{}{
+				"status": "open", // string instead of enum
+			},
+			want: false,
+		},
+		{
+			name: "status as enum - unchanged",
+			existing: &types.Issue{
+				Status: types.StatusInProgress,
+			},
+			updates: map[string]interface{}{
+				"status": types.StatusInProgress, // enum
+			},
+			want: false,
+		},
+		{
+			name: "issue_type as string vs enum - unchanged",
+			existing: &types.Issue{
+				IssueType: types.TypeBug,
+			},
+			updates: map[string]interface{}{
+				"issue_type": "bug", // string instead of enum
+			},
+			want: false,
+		},
+		{
+			name: "priority as int - unchanged",
+			existing: &types.Issue{
+				Priority: 3,
+			},
+			updates: map[string]interface{}{
+				"priority": 3,
+			},
+			want: false,
+		},
+		{
+			name: "priority as int64 - unchanged",
+			existing: &types.Issue{
+				Priority: 2,
+			},
+			updates: map[string]interface{}{
+				"priority": int64(2),
+			},
+			want: false,
+		},
+		{
+			name: "priority as float64 whole number - unchanged",
+			existing: &types.Issue{
+				Priority: 1,
+			},
+			updates: map[string]interface{}{
+				"priority": float64(1),
+			},
+			want: false,
+		},
+		{
+			name: "priority as float64 fractional - changed",
+			existing: &types.Issue{
+				Priority: 1,
+			},
+			updates: map[string]interface{}{
+				"priority": 1.5, // fractional not allowed
+			},
+			want: true,
+		},
+		{
+			name: "empty string vs empty - unchanged",
+			existing: &types.Issue{
+				Design: "",
+			},
+			updates: map[string]interface{}{
+				"design": "",
+			},
+			want: false,
+		},
+		{
+			name: "empty string vs nil - unchanged (treated as equal)",
+			existing: &types.Issue{
+				Assignee: "",
+			},
+			updates: map[string]interface{}{
+				"assignee": nil,
+			},
+			want: false,
+		},
+		{
+			name: "non-empty to empty - changed",
+			existing: &types.Issue{
+				Notes: "Some notes",
+			},
+			updates: map[string]interface{}{
+				"notes": "",
+			},
+			want: true,
+		},
+		{
+			name: "external_ref nil vs empty - unchanged",
+			existing: &types.Issue{
+				ExternalRef: nil,
+			},
+			updates: map[string]interface{}{
+				"external_ref": nil,
+			},
+			want: false,
+		},
+		{
+			name: "external_ref pointer to empty vs nil - unchanged",
+			existing: &types.Issue{
+				ExternalRef: strPtr(""),
+			},
+			updates: map[string]interface{}{
+				"external_ref": nil,
+			},
+			want: false,
+		},
+		{
+			name: "external_ref changed",
+			existing: &types.Issue{
+				ExternalRef: strPtr("gh-123"),
+			},
+			updates: map[string]interface{}{
+				"external_ref": "gh-456",
+			},
+			want: true,
+		},
+		{
+			name: "unknown field - treated as changed",
+			existing: &types.Issue{
+				Title: "Test",
+			},
+			updates: map[string]interface{}{
+				"title":        "Test",
+				"unknown_field": "value",
+			},
+			want: true,
+		},
+		{
+			name: "invalid type for title - treated as changed",
+			existing: &types.Issue{
+				Title: "Test",
+			},
+			updates: map[string]interface{}{
+				"title": 123, // wrong type
+			},
+			want: true,
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			got := issueDataChanged(tt.existing, tt.updates)
+			if got != tt.want {
+				t.Errorf("issueDataChanged() = %v, want %v", got, tt.want)
+			}
+		})
+	}
+}
+
+// strPtr helper for tests
+func strPtr(s string) *string {
+	return &s
+}
+
 // TestIdempotentImportNoTimestampChurn verifies that importing unchanged issues
 // does not update their timestamps (bd-84)
 func TestIdempotentImportNoTimestampChurn(t *testing.T) {