[MOD-18624] Cover tiered get_vector and read uint8 vectors back

[dor-forer]

What

Two independent gaps around the Python get_vector(), both on uncompressed indexes.

1. Tiered get_vector() has no test coverage. The dispatcher used to cast every non brute force index to HNSWIndex, so a tiered index failed the cast and the null result was dereferenced (SIGSEGV). #1045 replaced that cast with a tiered-first one, which fixed the crash but left the behavior untested: every tiered read in the flow tests runs after wait_for_index(), so nothing exercises a read while the vector is still in the flat buffer.

This adds test_get_vector and test_get_vector_multi to tests/flow/test_hnsw_tiered.py. Both read a label back before and after ingestion drains, and assert an absent label is reported as no vectors. The multi case asserts a count range before draining: an ingest job inserts into the backend before removing from the buffer, so a vector caught inside that window is reported by both tiers.

2. getVector() had no uint8 branch. Reading a uint8 vector back raised RuntimeError: Invalid vector data type, even though uint8 is supported everywhere else in the bindings (knn_query, range_query, index construction). Adds the branch, plus a read-back test for int8 and uint8 in tests/flow/test_hnsw.py.

Verification

Built the Python bindings and ran the flow tests on a Linux x86_64 box:

• Without the uint8 branch: TestUINT8::test_get_vector fails with RuntimeError: Invalid vector data type; TestINT8::test_get_vector passes.
• With it: both pass.
• Full tests/flow/test_hnsw_tiered.py: 21 passed.
• The reported reproducer (tiered get_vector after add_vector + wait_for_index) returns (1, 64) with the inserted values, no SIGSEGV.
• check-format.sh clean.

Not included

SQ8 tiered coverage. HNSWParams::quantType is not exposed to Python on main, so the SQ8 half of MOD-18624 belongs with #1048, which adds that binding. MOD-18624 stays open until that test lands there.

🤖 Generated with Claude Code

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Note

Low Risk
Small binding branch plus test-only coverage; no auth or core query-path logic changes beyond aligning UINT8 with existing INT8 read-back behavior.

Overview
Fixes Python get_vector() for UINT8 indexes and adds flow tests for get_vector on plain HNSW and tiered HNSW.

In bindings.cpp, getVector now handles VecSimType_UINT8 (same pattern as INT8: uint8_t storage returned as float numpy), so UINT8 read-back no longer raises Invalid vector data type.

test_hnsw.py adds a shared get_vector check on the cached L2 index (exact round-trip for int types, empty (0, dim) for missing labels) and wires test_get_vector into TestINT8 and TestUINT8.

test_hnsw_tiered.py adds test_get_vector and test_get_vector_multi, reading labels before wait_for_index() (buffer vs backend) and after drain; the multi test allows up to 2 * per_label rows mid-ingest when both tiers briefly report the same vector.

^{Reviewed by Cursor Bugbot for commit 2c7378c. Bugbot is set up for automated code reviews on this repo. Configure here.}

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 97.49%. Comparing base (26ffef5) to head (2c7378c).
⚠️ Report is 2 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1049      +/-   ##
==========================================
- Coverage   97.50%   97.49%   -0.02%     
==========================================
  Files         141      141              
  Lines        8851     8851              
==========================================
- Hits         8630     8629       -1     
- Misses        221      222       +1     

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