[Mark Hildebrand (hildebrandmw)]

Move frozen point knowledge out of Store and into Representations.

This is part of a workstream to make usage of start points more flexible. Currently, the Store has knowledge of frozen points and mandates that they go at the end. However, outside of some minor optimizations with respect to initial ID minting and ID scanning, the Store doesn't really need to know about frozen points.

The PR is broken into two commits:

Commit 1

Mechanically moves the start points handling into repr::Full and repr::Quantized and does minimal test rewrites on Store to compensate for the lack for direct frozen point knowledge.

Commit 2

A clean up pass. Instead of using std::ops::Range<u32> to represent start point ranges, this adds a bespoke Range that is closer to https://doc.rust-lang.org/std/range/struct.Range.html with the additional requirement that end >= start.

Small Perf Changes

When the Store/Freelist knew about the frozen points, we could optimize ID minting and ID scanning to not consider the frozen point range. With this PR, the Store doesn't know the start points are special. I think this is only a minor concern: there are usually only a handful of start points (usually one) for millions of vectors. So we add a few extra slot acquisition attempts but buy much more flexibility.

[Copilot]

🟡 Changes recommended

Frozen IDs in the freelist can exhaust all 20 acquisition attempts, causing Store::acquire to return None even when a writable slot is available.

1 open issue

• Prevent frozen IDs from exhausting slot acquisition retries · New

What changed in this PR

This PR moves start-point ownership from Store into the full and quantized representations, preparing the in-memory index for more flexible start-point placement.

Changes:

• Makes stores and freelists manage a total ID limit without tracking a separate frozen-point range.
• Moves capacity, start-point IDs, and total-point validation into representations.
• Adds a copyable, validated Range type and updates accessors, integration wrappers, and tests.

File	Description
diskann-inmem/​src/​store/​simple.rs	Updates tests to initialize frozen slots explicitly.
diskann-inmem/​src/​store/​mod.rs	Removes frozen-range ownership and uses total ID limits.
diskann-inmem/​src/​store/​intrusive.rs	Adapts frozen-slot and acquisition tests.
diskann-inmem/​src/​repr/​quantized/​mod.rs	Owns capacity and start-point IDs in the quantized representation.
diskann-inmem/​src/​repr/​internal/​simple.rs	Updates test store construction.
diskann-inmem/​src/​repr/​internal/​quantization/​rerank.rs	Updates reranking test store construction.
diskann-inmem/​src/​repr/​internal/​macros.rs	Reads capacity from representations.
diskann-inmem/​src/​repr/​full.rs	Owns capacity and start-point IDs in the full representation.
diskann-inmem/​src/​provider.rs	Uses the new range type for search start points.
diskann-inmem/​src/​num.rs	Adds validated ranges and boundary tests.
diskann-inmem/​src/​integration/​store/​simple.rs	Converts configured capacity into an ID limit.
diskann-inmem/​src/​integration/​store/​mod.rs	Reports slot counts from the total ID limit.
diskann-inmem/​src/​integration/​store/​intrusive.rs	Adapts construction and panic documentation.
diskann-inmem/​src/​integration/​store/​checked.rs	Adapts checked-store construction.
diskann-inmem/​src/​freelist.rs	Uses IdLimit for minting, scanning, and recycling bounds.

_{Review effort: Balanced}

[Codecov Comments Bot (codecov-commenter)]

Codecov Report

❌ Patch coverage is 98.51485% with 3 lines in your changes missing coverage. Please review.
✅ Project coverage is 92.10%. Comparing base (b83da5b) to head (3d95c32).

Files with missing lines	Patch %	Lines
diskann-inmem/src/freelist.rs	90.90%	1 Missing ⚠️
diskann-inmem/src/num.rs	98.83%	1 Missing ⚠️
diskann-inmem/src/repr/full.rs	94.11%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1527      +/-   ##
==========================================
+ Coverage   91.04%   92.10%   +1.05%     
==========================================
  Files         592      592              
  Lines      123565   123658      +93     
==========================================
+ Hits       112498   113890    +1392     
+ Misses      11067     9768    -1299     

Flag	Coverage Δ
miri	92.10% <98.51%> (+1.05%)	⬆️
unittests	92.04% <98.51%> (+1.29%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Files with missing lines	Coverage Δ
diskann-inmem/src/integration/store/checked.rs	100.00% <100.00%> (ø)
diskann-inmem/src/integration/store/intrusive.rs	100.00% <100.00%> (ø)
diskann-inmem/src/integration/store/mod.rs	96.55% <100.00%> (ø)
diskann-inmem/src/integration/store/simple.rs	100.00% <100.00%> (ø)
diskann-inmem/src/provider.rs	96.28% <100.00%> (ø)
diskann-inmem/src/repr/internal/macros.rs	100.00% <100.00%> (ø)
...ann-inmem/src/repr/internal/quantization/rerank.rs	98.75% <100.00%> (ø)
diskann-inmem/src/repr/internal/simple.rs	95.55% <100.00%> (ø)
diskann-inmem/src/repr/quantized/mod.rs	98.45% <100.00%> (+0.02%)	⬆️
diskann-inmem/src/store/intrusive.rs	93.95% <100.00%> (-0.03%)	⬇️
... and 5 more

... and 49 files with indirect coverage changes

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