File Change Set As Founding

File a held balance sheet as the company's FOUNDING balance sheet (accountant) — ZET-395.

A balance sheet uploaded as a document (or, over the API, onboarded) that is dated inside the company's first fiscal year, before its end, with no earlier year, is not accepted as that year's closing sheet unseen: it is held as a pending balances change set whose summary.founding_question is true, and the caller answers the question "founding balance sheet (Gründungsbilanz) or closing sheet?" (an interim sheet is answered with .../interim):

• closing sheet → POST .../change-sets/{set_id}/apply (the ordinary consent);
• founding sheet → this call. The held sheet's lines and date are stored exactly as create_balance_sheet with founding=true stores them (status founding, filed under that year, replacing an earlier founding sheet), and the change set is discarded so the sheet never becomes the year's closing sheet. generate_opening_entries for that year then opens from it, posting on its date.

An optional body {"edits": [...]} corrects the held lines as part of the answer (owner ruling 2026-09-30): the same per-line edit as PUT /balance-sheets/{id}/lines (line_id + final side / absolute amount_cents / is_contra; an edited line counts as reviewed). The edits go into the founding sheet only — the held sheet is not rewritten — and every check below runs on the edited lines.

apply-all never answers the question: such sets are left pending (counted skipped). 422 invalid.foundingBalanceSheet when the sheet cannot be a founding sheet (an earlier fiscal year or a prior-year closing sheet exists, it does not balance, a line still needs review, an edit names a line not on the sheet) — nothing changes; 409 when the set is no longer pending.