fix(seekdb): fix ann_search returning no rows in embedded mode

[whhe]

Summary

Fixes two bugs that caused ann_search to always fail when using embedded SeekDB
(ObVecClient(path=...) / SeekdbRemoteClient(path=...)).

Also fixes two broken test assertions introduced by a Copilot suggestion on PR #65.

Changes

• seekdb_engine.py: Set cursor._description = [] (not None) when a SELECT/SHOW/DESCRIBE returns 0 rows, so SQLAlchemy creates a row-returning CursorResult instead of _NoResultMetaData — which raised ResourceClosedError on fetchall().
• seekdb_engine.py: Store the embedded server reference via engine.update_execution_options(seekdb_server=server) (public API) so the flush helper can reach it without touching private Engine attributes.
• ob_client.py: Add _flush_seekdb_index() and call it at the end of insert(). HNSW index builds in seekdb are async; without an explicit flush, ann_search queries the index before it is built and returns 0 rows. The helper is a no-op for non-seekdb engines and for seekdb versions < 1.3.0. Refresh failures are demoted to a logger.warning so a flush error never aborts a successful write.
• ob_vec_client.py: Buffer results from ann_search, post_ann_search, and precise_search using Result.freeze()() (SQLAlchemy's built-in buffering) instead of a bespoke _BufferedResult wrapper. This preserves the full SQLAlchemy Result interface (.first(), .scalars(), .mappings(), etc.) for callers.
• tests/test_fts_index.py: Fix two assertions in FtsAnalyzerCompilationTest that expected PARSER_PROPERTIES = (...) with a space after =; the actual DDL output and reflection regex both use PARSER_PROPERTIES=(...) without a space.

Motivation

With embedded SeekDB, every call to ann_search raised sqlalchemy.exc.ResourceClosedError. The root causes were:

1. Connection lifetime: ann_search returned conn.execute() directly from inside a with engine.connect() block. Once the block exited the connection closed, leaving callers with a dead CursorResult.
2. Empty-SELECT cursor metadata: When _execute_via_pyseekdb returns [] (e.g., HNSW index not yet built), _SeekdbCursor set _description = None, which caused SQLAlchemy to mark the result as non-row-returning.
3. Async HNSW build: seekdb builds HNSW indexes asynchronously. Any ann_search immediately after insert finds an empty index until a CALL dbms_index_manager.refresh() flush is issued (supported from seekdb ≥ 1.3.0).

[Copilot]

Pull request overview

This PR fixes embedded SeekDB ann_search correctness by addressing result-lifecycle and cursor-metadata edge cases, and by ensuring async HNSW index builds are flushed before querying. It also aligns FTS analyzer test assertions with the actual emitted DDL formatting.

Changes:

• Ensure empty row-returning statements in embedded SeekDB produce a row-returning SQLAlchemy result (avoids ResourceClosedError on fetchall()).
• Add an embedded SeekDB index flush after inserts to avoid querying before the async HNSW build completes.
• Buffer/vector-search query results so they remain consumable after leaving the connection context; update FTS test assertions for parser properties formatting.

Reviewed changes

Copilot reviewed 3 out of 4 changed files in this pull request and generated 7 comments.

File	Description
tests/test_fts_index.py	Fixes analyzer DDL assertion strings to match emitted PARSER_PROPERTIES formatting.
pyobvector/client/seekdb_engine.py	Adjusts empty-query cursor metadata handling; stores embedded server reference on the engine for later index refresh.
pyobvector/client/ob_client.py	Adds a post-insert() embedded SeekDB index flush helper.
pyobvector/client/ob_vec_client.py	Buffers results returned from vector search methods to avoid dead results after connection closure.

---

💡 Add Copilot custom instructions for smarter, more guided reviews. Learn how to get started.

[Copilot]

Pull request overview

Copilot reviewed 3 out of 4 changed files in this pull request and generated 2 comments.

[Copilot]

Copilot encountered an error and was unable to review this pull request. You can try again by re-requesting a review.

[Copilot]

Pull request overview

Copilot reviewed 3 out of 4 changed files in this pull request and generated no new comments.