Phase 3 lays two orthogonal per-KB knobs in the data and API layers so
follow-up commits (Phase 3B-late, Phase 3B-multimodal) only need to add
their code path and UI selector, not schema or types.
Schema (studio/backend/storage/studio_db.py)
- rag_knowledge_bases gains chunking_strategy ('standard'|'late', default
'standard') and mode ('text'|'multimodal', default 'text'). Both are
immutable after KB creation — changing either invalidates existing
chunks because they were ingested through a specific pipeline.
- rag_chunks gains kind ('text'|'image'|'caption', default 'text'),
image_path (NULLABLE), linked_chunk_id (NULLABLE) — used by Phase
3B-multimodal to pair image chunks with their captions.
- Idempotent ALTER TABLE additions for existing installs (mirrors the
chat_threads display_name / *_code_exec_container_id pattern earlier
in the file).
API (studio/backend/routes/rag.py)
- ChunkingStrategy + KBMode Literal aliases.
- CreateKBRequest accepts both fields with backward-compat defaults.
- KBResponse exposes both.
- _validate_mode_combo rejects (multimodal, late) with 400 — no public
open-weight embedder supports both at once. Surface the constraint
early rather than failing silently during ingestion.
Config (studio/backend/utils/rag/config.py)
- RAG_EMBEDDER_MATRIX dict keyed by (mode, strategy) → embedder name.
- resolve_embedder() helper falls back to RAG_EMBEDDING_MODEL for legacy
KBs that pre-date the columns.
- (multimodal, late) intentionally absent.
Frontend (studio/frontend/src/features/rag/)
- api/rag-api.ts: ChunkingStrategy + KBMode types; KnowledgeBase
interface and createKnowledgeBase request type updated.
- stores/rag-store.ts: createKB signature uses the shared request type.
No user-visible UI changes yet — the only currently-usable combination
is (text, standard), so adding one-option selectors would be UX noise.
Phase 3B-late and Phase 3B-multimodal each add the relevant selector
option as part of shipping the code path.
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