Sanitise and deduplicate scenario sheet names 🟩

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

infrastructure/xlsx/scenario_export_workbook.py

@@ -8,6 +8,7 @@ dynamic number of scenario sheets is handled natively.
 
 from __future__ import annotations
 
+import re
 from io import BytesIO
 from typing import Sequence
 
@@ -15,6 +16,24 @@ from openpyxl import Workbook
 
 from domain.scenario_export.scenario_sheet import ExportSheet
 
+# Excel forbids these in a sheet title and caps titles at 31 characters.
+_ILLEGAL_SHEET_CHARS = re.compile(r"[:\\/?*\[\]]")
+_MAX_SHEET_NAME = 31
+
+
+def _safe_sheet_name(name: str, used: set[str]) -> str:
+    """An Excel-legal, unique sheet name: illegal characters stripped, capped at
+    31 chars, and suffixed on collision (two scenarios can share a name)."""
+    clean = _ILLEGAL_SHEET_CHARS.sub("", name or "scenario").strip() or "scenario"
+    clean = clean[:_MAX_SHEET_NAME]
+    base, index = clean, 1
+    while clean in used:
+        suffix = f" ({index})"
+        clean = base[: _MAX_SHEET_NAME - len(suffix)] + suffix
+        index += 1
+    used.add(clean)
+    return clean
+
 
 def render_workbook(sheets: Sequence[tuple[str, ExportSheet]]) -> bytes:
     """Render the scenario sheets into a single branded ``.xlsx`` as bytes. Each
@@ -25,8 +44,9 @@ def render_workbook(sheets: Sequence[tuple[str, ExportSheet]]) -> bytes:
     if default is not None:
         workbook.remove(default)
 
+    used_names: set[str] = set()
     for name, sheet in sheets:
-        worksheet = workbook.create_sheet(title=name)
+        worksheet = workbook.create_sheet(title=_safe_sheet_name(name, used_names))
         worksheet.append(list(sheet.columns))
         for row in sheet.rows:
             worksheet.append([row.get(column, "") for column in sheet.columns])