[1.6.0] - 2026-04-19

Added

• BM25 + RRF Hybrid Search (engine/hybrid_search.py): Production-grade BM25
  (k1=1.5, b=0.75) with Korean+English tokenizer
  (re.findall(r"[a-z0-9\uac00-\ud7a3]+", text.lower())).
  Reciprocal Rank Fusion merges BM25 and ChronosGrid semantic lists using
  string URI as doc ID — no integer alignment required. k=60, top_k configurable.
  Lazy per-store index with _bm25_dirty set: index rebuilt on first hybrid
  search after any upload, not on every upload.

• KnowledgeAtom chunk-level indexing (engine/knowledge_atom.py): Two-level
  indexing — file-level doc + chunk atoms with fragment URIs
  (local://store/enc_path#c0001). chunk_and_inject() splits content into
  800-char overlapping windows (120-char overlap, 80-char minimum), embeds each
  chunk via embedding_generator.generate(), injects into ChronosGrid, and
  registers in _atom_store_docs for URI-based resolution. Enables precision
  chunk-level retrieval alongside file-level documents.

• Stable URI scheme: Local documents now use
  local://<store>/<urllib.parse.quote(abs_path, safe='')> instead of
  local://<store>/<basename>. Eliminates collisions when files with identical
  names exist in different directories. URIs are reversible via unquote().
  Both main docs and chunk atoms share the same URI namespace.

Refactored

• core.py segmentation (1258 → 221 lines): FlamehavenFileSearch split into
  three focused mixin classes via IngestMixin, LocalSearchMixin,
  CloudSearchMixin. core.py is now a thin orchestrator: __init__,
  create_store, list_stores, delete_store, get_metrics,
  _resolve_vector_backend.

  Mixin	File	Responsibility
  IngestMixin	_ingest.py (228 L)	upload_file, upload_files, _local_upload, _generate_file_vector
  LocalSearchMixin	_search_local.py (273 L)	_local_search, BM25 rebuild, hybrid rerank, RAG prompt
  CloudSearchMixin	_search_cloud.py (265 L)	search, search_stream, search_multimodal + 6 shared helpers

• Duplicate helper elimination (_search_cloud.py): Six blocks that were
  copy-pasted between search() and search_multimodal() are now shared helpers:
  _resolve_search_params, _ensure_store, _query_vector_backend,
  _driftlock_validate, _extract_grounding_sources, _gemini_search_call.

Fixed

• search_stream double intent-refine bug: intent_refiner.refine_intent(query)
  was called twice (lines 984 and 988 in old core.py) — once before the
  provider-RAG branch and once inside it. The second call discarded the first
  optimized_query. Fixed: single call, result reused throughout the method.

Tests

• 443 tests pass, 13 skipped — no regression from refactor.
• test_flamehaven_remote_client_flow patch target updated: also patches
  flamehaven_filesearch._search_cloud._google_genai_types after types moved
  from core.py to _search_cloud.py.