Implement filter search for disk path using AdpativeL

[dyhyfu]

This PR is to add filter search to disk path using AdpativeL filter algorithm.

Reference PR: #1131

The main changes:

1. New filter_search() method on DiskIndexSearcher (parallel to flat_search) that constructs InlineFilterSearch::new(Knn, label_provider, adaptive_l) and hands it to the same self.index.search(...) engine as the plain Knn path.
2. New PredicateLabelProvider that adapts the existing &dyn Fn(&u32) -> bool to QueryLabelProvider
3. search() and search_internal() gain adaptive_l: Option. When None, behavior is identical to today. When Some(_), the graph path routes through filter_search.
4. Three-way dispatch in search_internal: flat scan → graph + adaptive_l → plain Knn.

[Copilot]

Pull request overview

This PR adds an AdaptiveL-enabled, inline label-filtered graph-search path for disk index search, wiring it through DiskIndexSearcher while keeping existing behavior unchanged when AdaptiveL is not provided.

Changes:

• Add adaptive_l: Option<AdaptiveL> to DiskIndexSearcher::search / search_internal and dispatch to an InlineFilterSearch path when present.
• Introduce a small PredicateLabelProvider adapter to bridge the existing &dyn Fn(&u32) -> bool filter predicate into QueryLabelProvider<u32>.
• Add disk-provider tests covering (1) no-op equivalence vs plain Knn and (2) selective predicates returning only matching IDs; update callers to pass None until CLI/JSON exposes AdaptiveL.

Reviewed changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated 1 comment.

File	Description
diskann-tools/src/utils/search_disk_index.rs	Passes None for the new adaptive_l argument (not yet exposed via CLI).
diskann-disk/src/search/provider/disk_provider.rs	Implements filter_search via InlineFilterSearch + AdaptiveL, adds adapter + tests, and extends search APIs with adaptive_l.
diskann-disk/src/build/builder/core.rs	Updates test call sites to include the new adaptive_l parameter.
diskann-benchmark/src/backend/disk_index/search.rs	Passes None for the new adaptive_l argument (not yet exposed via benchmark JSON).

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[magdalendobson]

You may want to take a look at the changes that are coming to filters with #1141 and make sure your changes are compatible

[wuw92]

Worth noting this whole module diskann-tools/src/utils/search_disk_index.r looks dead. pub fn search_disk_index / SearchDiskIndexParameters aren't referenced from any binary.
I recommend deleting search_disk_index.rs (and its pub mod / pub use in utils/mod.rs) in a follow-up rather than carry the filter search migration.

[wuw92]

nit: Plan  tends to read as a query/execution plan: something the engine generates and optimize. Consdier naming SearchMode  or  SearchKind  which would line up more directly with what the variants express

[dyhyfu]

Renamed to SearchMode

[codecov-commenter]

Codecov Report

❌ Patch coverage is 90.75630% with 22 lines in your changes missing coverage. Please review.
✅ Project coverage is 89.47%. Comparing base (3aa44ac) to head (d1dcec3).

Files with missing lines	Patch %	Lines
diskann-disk/src/search/provider/disk_provider.rs	93.25%	11 Missing ⚠️
diskann-tools/src/utils/search_disk_index.rs	0.00%	7 Missing ⚠️
diskann-disk/src/search/search_mode.rs	94.02%	4 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1173      +/-   ##
==========================================
+ Coverage   89.46%   89.47%   +0.01%     
==========================================
  Files         487      488       +1     
  Lines       92170    92363     +193     
==========================================
+ Hits        82460    82642     +182     
- Misses       9710     9721      +11     

Flag	Coverage Δ
miri	89.47% <90.75%> (+0.01%)	⬆️
unittests	89.12% <90.75%> (+0.01%)	⬆️

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

Files with missing lines	Coverage Δ
diskann-benchmark/src/main.rs	91.36% <ø> (ø)
diskann-disk/src/build/builder/core.rs	95.36% <100.00%> (+0.01%)	⬆️
diskann-disk/src/search/search_mode.rs	94.02% <94.02%> (ø)
diskann-tools/src/utils/search_disk_index.rs	0.00% <0.00%> (ø)
diskann-disk/src/search/provider/disk_provider.rs	93.56% <93.25%> (-0.12%)	⬇️

... and 1 file with indirect coverage changes

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[magdalendobson]

Can we expose adaptive L by creating a json deserializable struct here that has a function returning the SearchMode object? It's a bit awkward to just construct it from params here. If we had a dedicated struct it would be much easier to build on what's already here.

[magdalendobson]

This looks fine to me pending a couple of things:

• Let's get the benchmark integration a little smoother by creating a wrapper struct that's json deserializable and constructs the SearchMode directly
• Can you include a few experiments with larger filtered datasets as a sanity check for correctness/performance here?