"""Compatibility for Gemini translators that retain only the last system turn.

Only instruction-bearing text messages are folded; user/tool content is never
promoted. Caller must scope this to the affected Gemini route. No network or IO.
"""


def coalesce_context(request):
    items = request.get('input')
    base = request.get('instructions', '')
    if not isinstance(items, list) or not isinstance(base, str):
        return 0
    chunks = ['[BASE SYSTEM INSTRUCTIONS]\n' + base] if base else []
    remaining = []
    count = 0
    for item in items:
        if not isinstance(item, dict) or item.get('type', 'message') != 'message' or item.get('role') not in ('system', 'developer'):
            remaining.append(item)
            continue
        content = item.get('content', '')
        if isinstance(content, str):
            text = content
        elif isinstance(content, list) and all(isinstance(p, dict) and p.get('type') in ('input_text','text') and isinstance(p.get('text'), str) for p in content):
            text = '\n'.join(p['text'] for p in content)
        else:
            # Unknown multimodal instruction block: do not discard or rewrite.
            return 0
        chunks.append('[' + item['role'].upper() + ' CONTEXT ' + str(count+1) + ']\n' + text)
        count += 1
    if count:
        request['instructions'] = '\n\n'.join(chunks)
        request['input'] = remaining
    return count