Extract safecsv writer for spreadsheet-safe exports

Wrap encoding/csv with formula-safe cell sanitization and
use it from log export streaming.

Signed-off-by: Cursor Agent <cursoragent@cursor.com>

Co-authored-by: Bryan FRIMIN <bryan@frimin.fr>

pkg/safecsv/cell.go

@@ -0,0 +1,49 @@
+// Copyright (c) 2026 Probo Inc <hello@probo.com>.
+//
+// Permission is hereby granted, free of charge, to any person obtaining a copy
+// of this software and associated documentation files (the "Software"), to deal
+// in the Software without restriction, including without limitation the rights
+// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+// copies of the Software, and to permit persons to whom the Software is
+// furnished to do so, subject to the following conditions:
+//
+// The above copyright notice and this permission notice shall be included in
+// all copies or substantial portions of the Software.
+//
+// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+// SOFTWARE.
+
+package safecsv
+
+// SanitizeRecord returns a copy of record with spreadsheet-safe cell values.
+func SanitizeRecord(record []string) []string {
+	if len(record) == 0 {
+		return record
+	}
+
+	out := make([]string, len(record))
+	for i, field := range record {
+		out[i] = SanitizeCell(field)
+	}
+
+	return out
+}
+
+// SanitizeCell prefixes values that spreadsheet tools may interpret as formulas.
+func SanitizeCell(value string) string {
+	if value == "" {
+		return value
+	}
+
+	switch value[0] {
+	case '=', '+', '-', '@', '\t', '\r':
+		return "'" + value
+	default:
+		return value
+	}
+}