Update Taxonomy Block

Incrementally mutate a taxonomy block via typed delta lists (elements/structures/associations/rules to add, update, remove). Dispatches by the target taxonomy's stored taxonomy_type. For a chart of accounts: add, rename and reclassify accounts freely; an account with facts or line items is never removed — retire it with elements_to_update[].is_active=false (history stays, new postings are refused, pickers hide it; true reactivates). Removal and whole-chart delete work only with no activity. Library-origin block types (reporting_standard) surface 501. reporting_extension / custom_ontology authoring may be disabled per environment (TAXONOMY_AUTHORING_ENABLED) — disabled surfaces 403. Closed months are immutable against curation: a mapping arc added or removed for an account with landed history in a closed month, or a balance_type / period_type / trait change on such an account, is refused (422, protected_facts) naming the months to reopen first. An envelope that removes an account's arc and adds one on the same primary statement moves it: a reclassification, allowed.

Idempotency: supply an Idempotency-Key header to make safe retries; replays within 24 hours return the same envelope. Reusing the key with a different body returns HTTP 409 Conflict.