Function replace_chunks 

async fn replace_chunks(
    pool: &SqlitePool,
    document_id: &str,
    chunks: &[Chunk],
) -> Result<()>

Atomically replaces all chunks (and their embeddings/FTS entries) for a document.

This function runs inside a single SQLite transaction to ensure consistency:

1. Deletes old chunk_vectors rows for the document’s chunks.
2. Deletes old embeddings metadata rows for the document’s chunks.
3. Deletes old chunks_fts (FTS5) entries for the document.
4. Deletes old chunks rows for the document.
5. Inserts new chunks and their corresponding FTS entries.

Arguments

• pool — the database connection pool.
• document_id — the UUID of the parent document.
• chunks — the new set of chunks to insert.