[MayCXC]

A point query on a rowid the table does not hold returns no rows on a flat column, and fails on a rescore or DiskANN column:

create virtual table t using vec0(embedding float[8] indexed by rescore(quantizer=bit));
insert into t(rowid, embedding) values (1, ?);   -- any float[8]
select rowid from t where rowid = 999;
-- Error: Could not fetch vector data for 999 from rescore vectors

The same happens with quantizer=int8, for a rowid that was deleted, and on a DiskANN column (Could not fetch vector data for 999 from DiskANN vectors table). An IVF column already returns no rows.

vec0_get_vector_data() looks the rowid up in _rowids with vec0_get_chunk_position(), whose SQLITE_EMPTY vec0Filter_point() reads as the end of the results, but only on the flat path; the DiskANN and rescore branches come first and read their own tables by rowid, where a missing row is an error. Every index type registers its rows in _rowids (the insert's first step, an all-DiskANN table included, which skips only the chunk placement), so the lookup now comes before every index's read. Its other callers, vec0Column_fullscan() and vec0Column_knn(), read rowids taken from _rowids or from a KNN result.

Test. tests/test-rescore.py (both quantizers), tests/test-diskann.py and tests/test-ivf.py each check a never-inserted and a deleted rowid. On main the rescore and DiskANN tests fail with the errors above; on this branch they pass, and the IVF one passes on both. The Python tests pass: 242 passed and 67 skipped as make loadable builds, 305 passed and 4 skipped with -DSQLITE_VEC_EXPERIMENTAL_IVF_ENABLE=1. It merges cleanly with #327 to #331 and #336 to #341.

Origin. The rescore port to photostructure/sqlite-vec, photostructure#8 (cd4bb09), lists this among its differences from upstream, with the lookup first in vec0_get_vector_data() as here, and the DiskANN port, photostructure#11 (cd53413), tests it for DiskANN columns; the change and its tests are written here for asg017's main. No open or closed PR or issue here makes the same change.