#!/usr/bin/env python3
# Standalone synthetic fixture; no user files or external network.

import copy,json
initial=[{'id':f'R-{n}','version':1}for n in range(100,108)]
current=copy.deepcopy(initial);pages=[copy.deepcopy(current[:3])]
current.insert(0,{'id':'R-099','version':1});next(x for x in current if x['id']=='R-102')['version']=2
pages.extend([copy.deepcopy(current[3:6]),copy.deepcopy(current[6:9])])
ledger={};duplicates=[];conflicts=[]
for p,items in enumerate(pages,1):
    for item in items:
        if item['id']in ledger:
            duplicates.append({'id':item['id'],'page':p})
            if ledger[item['id']]!=item:conflicts.append({'id':item['id'],'old':ledger[item['id']],'new':item})
        else:ledger[item['id']]=item
missing=sorted({x['id']for x in current}-set(ledger));assert missing==['R-099'] and len(duplicates)==1 and len(conflicts)==1
chain={'start':{'items':initial[:3],'next':'middle-empty'},'middle-empty':{'items':[],'next':'last-a'},'last-a':{'items':initial[3:6],'next':'last-b'},'last-b':{'items':initial[6:],'next':''}}
def collect(responses):
    token='start';seen=set();data=[];trace=[]
    while token:
        if token in seen:raise ValueError('repeated continuation token')
        seen.add(token);response=responses[token];data+=response['items'];trace.append({'token':token,'count':len(response['items']),'next':response['next']});token=response['next']
    return data,trace
snapshot,trace=collect(chain);assert snapshot==initial
loopBlocked=False
try:collect({'start':{'items':[],'next':'start'}})
except ValueError:loopBlocked=True
assert loopBlocked
result={'initial':initial,'currentAfterMutation':current,'offsetPages':pages,'offsetAudit':{'received':sum(map(len,pages)),'unique':len(ledger),'duplicates':duplicates,'conflicts':conflicts,'missingAgainstKnownCurrent':missing},'snapshotCursor':{'trace':trace,'ids':[r['id']for r in snapshot],'completeAgainstInitial':True},'loopBlocked':True,'scope':'Deterministic local response fixtures, no vendor API requests. Missing IDs are knowable only because this fixture exposes a reference inventory. Cursor alone does not imply provider snapshot consistency.'}

import sys,json
from datetime import datetime,timezone
result={'experiment':'api-pagination-overlap-ledger','executedAt':datetime.now(timezone.utc).isoformat(),'runtime':sys.version.split()[0],'synthetic':True,**result}
print(json.dumps(result,ensure_ascii=False,indent=2))