---
model: openai/gpt-5.6-sol
service: opencode
timestamp: 2026-08-11T23:38:33Z
git_ref: 7cbd64ee
diff_cmd: git diff HEAD~1..HEAD
---

The user asked for a Tractor fix in a new isolated worktree after a live piker
failure reported:

```text
tractor.trionics._broadcast.Lagged:
Task `piker.brokers.ib.broker.handle_order_requests` overrun and
dropped `0` values
```

Inspection showed the lag exception was valid but its count was off by one.
`BroadcastReceiver.receive_nowait()` treats `seq` as a deque index. With a
one-entry queue, index zero is the only retained value and `seq == 1` already
means one value was displaced. The old `seq - maxlen` calculation therefore
reported zero instead of one.

> `git diff HEAD~1..HEAD -- tractor/trionics/_broadcast.py`

Adjusted the lag count to `seq - maxlen + 1` and documented why the first
invalid deque index must be included. The existing Tokio-style cursor reset
remains unchanged.

> `git diff HEAD~1..HEAD -- tests/test_task_broadcasting.py`

Added a deterministic parameterized regression covering a one-slot queue
with one dropped value and a three-slot queue with two dropped values. The
test keeps the root receiver idle while a child subscriber synchronously
drains each produced value, asserts the exact `Lagged` message, and proves the
next receive resumes at the oldest retained item.

Verification output:

```text
..                                                                       [100%]
2 passed in 0.04s

..........                                                               [100%]
10 passed in 4.65s
```

The targeted import resolved to the new Tractor worktree. Python compilation
and `git diff --check` passed. Adversarial review found no actionable issues;
zero-capacity channels remain a pre-existing untested edge outside this fix.