Generate Opening Entries

Generate Eröffnungsbuchungen for target_fiscal_year (accountant).

Orchestration (COMPANY_SETUP_FEATURE_PLAN §4.4):

1. txn 1 (short) — load settings + chart rows (target FY) + the accepted balance-sheet snapshot for target_fiscal_year - 1 (+ its lines) + the optional FiscalYearSummary + VAT rates; build the accountant request via the pure builder. 409 if there is no accepted prior-year snapshot (when one is held for acceptance, the message names its change set and residual); 422 if the builder refuses (needs_review lines / currency mismatch / unbalanced sheet).
2. accountant call — await the proposal without holding any DB transaction; 503 if accountant is unreachable/failed.
3. txn 2 (short) — persist the OpeningEntryProposal (request_json, request_hash, response, accountant_metadata, status, source_snapshot_id, opening_posting_date, generated_by) and return it.

Creating the required prior-year snapshot (ZET-159) — three paths, all consent-aware (first sheet for the FY auto-accepted when Σdebit and Σcredit agree within 1 ct; an unbalanced first sheet, or a conflicting one, lands proposed + a pending change set, consented via POST .../change-sets/{set_id}/apply):

• document upload — send the prior year's closing balance sheet through the accounting-documents intake (upload_intake / POST .../accounting-documents); the analyzer extracts and persists it;
• structured figures — POST /companies/{company_id}/balance-sheets (create_balance_sheet) with the closing balances as JSON lines, for the established tenant with no closing-sheet document; file them under the year being closed (target_fiscal_year - 1);
• from the ledger — POST .../balance-sheets/from-gl for a year that ran inside Zeno and is sealed.

A newly founded company (ZCT-843) opens its first year from its founding balance sheet: create_balance_sheet with founding=true, fiscal_year = the founding year itself and as_of_date = the founding date. An uploaded (or onboarded) sheet dated inside the company's first year before its end is held with the question summary.founding_question instead of being filed as a closing sheet (ZET-395) — answer it with POST .../change-sets/{set_id}/founding (or .../apply for the closing sheet). In any other year a sheet dated before the year's end is held with summary.interim_question — .../interim keeps it as an interim sheet that never opens a year, .../apply makes it the closing sheet (owner ruling 2026-09-30). A founding sheet is its own kind — it never competes with that year's closing sheet, and no other year's opening reads it. When the target year is the company's first fiscal year and such a sheet exists, generation uses it automatically, and the posting date defaults to its date (an explicit opening_posting_date wins); the posted entries carry source_action='founding'. With no prior year to carry accounts from, the sheet's accounts must already be in the target year's chart.

Opening balances on VAT control accounts are not taxable events. The generated proposal carries them (e.g. 1170/2200) untagged by design and the POST /opening-entries/{proposal_id}/post path books them without VAT codes. Only a hand-built manual opening JE hits the composition guard — there, body.not_vat=true is the intended treatment, not a workaround.