-- KB spine: document_chunk — unique-key fix + exclusion flag
-- Additive: does not modify 001_envelope.sql or 002_chunks.sql.
-- Version: 003 — chunk model key + excluded_reason (module 5, phase 3, plan §3.3)
--
-- (a) UNIQUE rozszerzony o model — bez tego drugi model embeddingów cicho się no-opuje
--     na ON CONFLICT DO NOTHING (finding z review kroku 6 fazy 2).
-- (b) excluded_reason — flaga wykluczenia chunka z retrievalu i kompilacji
--     (NULL = aktywny; 'ocr_junk' | 'duplicate').

ALTER TABLE document_chunk
    DROP CONSTRAINT IF EXISTS document_chunk_envelope_id_chunk_index_key;
ALTER TABLE document_chunk
    ADD CONSTRAINT document_chunk_envelope_chunk_model_key
    UNIQUE (envelope_id, chunk_index, model);

ALTER TABLE document_chunk
    ADD COLUMN IF NOT EXISTS excluded_reason TEXT;  -- NULL = aktywny