[Feature](lance) Add radius and full-text search modes

[Gabriel39]

Parent

Tracked by #66340. ANN and Flat vector search were introduced by #65730.

Scope

• Add Radius/Range Search with lower and upper distance bounds.
• Add standalone full-text search with BM25.
• Define result schemas, filtering order, scoring semantics, limits, and EXPLAIN output.
• Keep Hybrid Search out of scope unless it is designed separately.

Completion criteria

• FE analysis and BE/lance-c execution paths are implemented.
• Unit and regression tests cover bounds, BM25 scoring, filters, and invalid parameters.
• User documentation describes syntax, score or distance semantics, and limitations.
• Representative indexed and non-indexed datasets are verified.

Status update — 2026-09-30

Standalone full_text_search() is delivered by #67289 (merged into branch-4.1) with FE/BE tests and SQL regression coverage. Its recorded External Regression status is successful. English and Chinese syntax, result, filtering, scoring, coverage-mode, and parameter documentation merged in apache/doris-website#4112.

The unchecked shared scope/completion criteria still include Radius/Range Search. The upstream C/C++ distance-bound API is proposed in lance-format/lance-c#90, which is open; it does not yet provide Doris SQL/FE/BE integration or its tests and documentation. Keep this issue open for that work. Distributed BM25 global-statistics consistency is separately tracked in #67435; standalone FTS delivery does not imply that follow-up is complete.

For the parent feature matrix, completion on branch-4.1 is the branch criterion; no separate branch-4.2 merge is required.