# httpx Concurrent Client Cookie Corruption

## Symptom
All 30 parallel requests return HTTP 401, but individual tests succeed.

## Root Cause
Sharing ONE `httpx.AsyncClient` instance across multiple concurrent `asyncio` tasks corrupts cookie handling. httpx reuses connection pools and cookie jars that are not thread/async-safe when multiple tasks set different cookies.

## Wrong Pattern
```python
# ❌ Creates one shared client — cookies from different accounts mix up
async def main():
    async with httpx.AsyncClient(timeout=httpx.Timeout(30)) as shared_client:
        # All 30 concurrent tasks use the SAME client
        tasks = [test_account(shared_client, acc) for acc in accounts]
        await asyncio.gather(*tasks)

async def test_account(client, acc):
    # Setting cookies on the shared client
    client.cookies = {name: value}  # Gets overwritten by other tasks!
    r = await client.post(...)
```

## Correct Pattern
```python
# ✅ Each concurrent task creates its OWN client
async def test_account(acc):
    cookies = load_cookies(acc['cookies_path'])
    async with httpx.AsyncClient(cookies=cookies, timeout=httpx.Timeout(30)) as client:
        r = await client.post(...)

async def main():
    tasks = [test_account(acc) for acc in accounts]
    await asyncio.gather(*tasks)
```

## Concurrency Control
Use `asyncio.Semaphore(N)` to limit concurrent connections:
```python
sem = asyncio.Semaphore(3)

async def bounded(acc):
    async with sem:
        return await test_account(acc)

results = await asyncio.gather(*[bounded(a) for a in accounts])
```

## Detection
If you see HTTP 401 on all requests in parallel but HTTP 201 on individual sequential requests, this is almost certainly the shared client issue.