---
model: gpt-6 (exact variant not exposed)
service: codex
timestamp: 2026-09-24T16:57:57.342784+00:00
git_ref: 1da9b760
scope: code
substantive: true
raw_file: 20260924T165757Z_1da9b760_prompt_io.raw.md
---

## Prompt

Document and test the existing null-segment repair, including its
flat-bar fallback, while distinguishing packed timestamp gaps.

## Response summary

Documented SHM-only repair, provider placement assumptions, fallback
fields, notifications, and concurrency limits. Added boundary and
no-history coverage and fixed epoch-dependent comparison tolerance
which could synthesize a duplicate timestamp at the right margin.

## Files changed

- piker/tsp/_history.py: helper contract and absolute tolerance.
- tests/test_history_backfill.py: four additional parameter/case runs.

## Human edits

The human identified cancellation as a source of stored gaps,
correctly described packed indexes and insertion costs, pointed to
maybe_fill_null_segments(), and requested immediate documentation
and tests. No direct source edits observed during this change;
the patch remains uncommitted for review.

## Close-copy factoring follow-up

The human requested stronger internal types, a reusable close-copy
helper, searchable comments for copying close and synthesizing
stamps, and research into historical venue closure queries.
Extracted _copy_close_to_null_rows(), preserving non-OHLC fields and
rejecting occupied slots before mutation. Added explicit callback,
array, segment-index and date annotations. Preserved the existing
provenance TODO and suggested avoiding volume sentinels.
Four helper cases cover successful fill and unchanged rejected
inputs. Backfill suite: 19 passed in 2.01s; Ruff and diff check pass.

IB documents historical SCHEDULE requests separately from contract
hours. The installed ib_async exposes reqHistoricalScheduleAsync.
No live schedule request or venue behavior change was performed.
Source: https://interactivebrokers.github.io/tws-api/historical_bars.html