Resolves both 🟡 important issues from the latest review:
1. `page_number` was unconditionally overwritten in `viz_routes.py:696` even
when Qdrant's payload lacked the field, clobbering the value resolved
from `chunk_context.page_number`. The new helper returns each field
independently and both call sites only overwrite via `is not None`
guards, matching the existing logic in `visualization.py`.
2. The ~60-line `if chunk_index is not None: ... else: ...` Qdrant scroll
block was duplicated between `api/visualization.py` and
`auth/viz_routes.py`. Extracted into `get_chunk_bbox_and_page_from_qdrant`
in `search/context.py` alongside the existing private `_get_chunk_*_from_qdrant`
helpers; both routes now share ~12 lines of caller code.
New unit tests at `tests/unit/test_chunk_bbox_helper.py` cover the indexed
and offset paths, the `(bbox, None)` regression case, and graceful
degradation on Qdrant strict-mode 400 (which also closes nit #4).
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
