MOD-13176 Add Ad-Hoc Brute Force Context API for disk-based vector search

[meiravgri]

Overview

Introduces a new VecSimAdhocBfCtx abstraction to preprocess a query vector once and reuse it for repeated distance computations. This is the foundation for efficient hybrid ad-hoc brute force search on disk-based HNSW indexes.

Changes

• New VecSimAdhocBfCtx class inheriting from VecsimBaseObject
• New C API entrypoints:
  • VecSimIndex_AdhocBfCtx_New() - Create context for a query vector
  • VecSimIndex_AdhocBfCtx_Free() - Release context
  • VecSimIndex_AdhocBfCtx_GetDistanceFrom() - Get distance for a single label
  • VecSimIndex_AdhocBfCtx_GetExactDistances() - Batch-fetch exact distances for reranking
• New virtual method VecSimIndexInterface::newAdhocBfCtx() (defaults to nullptr for unsupported index types)
• Compile-time static_assert to enforce labelType == size_t at C/C++ boundary

Mark if applicable

• This PR introduces API changes
• This PR introduces serialization changes

---

Note

Medium Risk
Introduces a new public C API and virtual extension point for creating/freeing query contexts and computing distances, which can impact ABI/API consumers and allocator/lifetime handling if misused.

Overview
Adds a new ad-hoc brute force context abstraction (VecSimAdhocBfCtx) to preprocess a query once and reuse it for repeated distance computations (including a batched exact-distance path).

Exposes this via new C API entrypoints (VecSimIndex_AdhocBfCtx_New/Free/GetDistanceFrom/GetExactDistances) that delegate to a new virtual method VecSimIndexInterface::newAdhocBfCtx (defaulting to nullptr for unsupported index types). Also adds a compile-time static_assert to enforce labelType == size_t at the C/C++ boundary.

^{Written by Cursor Bugbot for commit 96b659e. This will update automatically on new commits. Configure here.}

[jit-ci]

🛡️ Jit Security Scan Results

✅ No security findings were detected in this PR

---

^{Security scan by Jit}

[codecov]

Codecov Report

❌ Patch coverage is 0% with 10 lines in your changes missing coverage. Please review.
✅ Project coverage is 97.01%. Comparing base (8d37cf1) to head (96b659e).
⚠️ Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
src/VecSim/vec_sim.cpp	0.00%	9 Missing ⚠️
src/VecSim/vec_sim_interface.h	0.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #917      +/-   ##
==========================================
- Coverage   97.14%   97.01%   -0.13%     
==========================================
  Files         129      129              
  Lines        7557     7567      +10     
==========================================
  Hits         7341     7341              
- Misses        216      226      +10     

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.

[cursor]

Cursor Bugbot has reviewed your changes and found 1 potential issue.

^{Bugbot Autofix is OFF. To automatically fix reported issues with cloud agents, have a team admin enable autofix in the Cursor dashboard.}