closes: a run of members closes splits cumulatively

Each close into members' capital rounded on its own, ties to the
earlier member, so twelve monthly 50/50 closes of odd-cent income could
leave one member several cents ahead of half the year (docs/testing.md
#12, found with the members' equity fix).

- CloseTo::Members now splits cumulatively over a run (closes back to
  back with the same members and shares): each close gives a member
  allocate(run total so far) - allocate(run total before). Periods
  record their close order and a cumulative close's members and net
  (Period::close_seq, member_close) so the next close continues the run
  and replay recomputes it exactly. A close to anything else, or other
  shares, ends the run.
- Journaled "rounding": "cumulative". The per-close rule is kept as
  CloseTo::MembersPerClose for closes journaled "largest_remainder";
  older closes still replay with the last member absorbing it.
- Lean: runPart_telescopes (a member's total from a run is their
  allocation of the run's total) and closePart_total (each close hands
  out exactly its net), audited to the standard axioms.
- Tests: hand-computed three one-cent months (per close A 0.03 / B 0;
  cumulative A 0.02 / B 0.01), a run ending, a property that each member
  stays within a cent of their share (fails on the per-close rule), and
  a store contract that each rule journals and replays as itself.

The first company's books have no closes yet, so all of theirs use the new rule.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01GWVo7x3UHw5kwCUaWxiejX

crates/ledger-core/src/periods.rs

@@ -51,8 +51,15 @@ pub enum CloseTo {
     /// Members' capital accounts by share (shares sum to 1): the
     /// partnership convention, where each member's capital account carries
     /// their allocated earnings and absorbs their distributions. Odd cents
-    /// go by largest remainder ([`allocate`]).
+    /// go by largest remainder ([`allocate`]), cumulatively: a run of
+    /// member closes with the same members and shares gives each member,
+    /// in total, their share of the run's total to the cent, so rounding
+    /// never piles up close after close (rules.md B-13; since 2026-10-13).
     Members(Vec<MemberClose>),
+    /// [`CloseTo::Members`] rounding each close on its own (largest
+    /// remainder), the rule for closes journaled on 2026-10-13 before the
+    /// cumulative one. Only replay of those journals produces it.
+    MembersPerClose(Vec<MemberClose>),
     /// [`CloseTo::Members`] under the rounding closes used before
     /// 2026-10-13 ([`allocate_last_absorbs`]). Only replay of those journals
     /// produces it; new closes use `Members`.
@@ -134,6 +141,23 @@ pub struct Period {
     pub status: PeriodStatus,
     /// The closing entry's id, once closed.
     pub closing_entry: Option<u64>,
+    /// The order it closed in among all closes (1 for the first), once
+    /// closed.
+    #[serde(default)]
+    pub close_seq: Option<u64>,
+    /// What a cumulative members close allocated, once closed that way.
+    #[serde(default)]
+    pub member_close: Option<MemberCloseRecord>,
+}
+
+/// A cumulative members close ([`CloseTo::Members`]): who shared, and the
+/// net it closed. The next close with the same members continues the run.
+#[derive(Clone, Debug, Serialize, Deserialize, PartialEq)]
+pub struct MemberCloseRecord {
+    /// (capital account, share), in the order given.
+    pub members: Vec<(crate::AccountId, rust_decimal::Decimal)>,
+    /// The net income this close allocated (negative for a loss).
+    pub net: rust_decimal::Decimal,
 }
 
 impl Period {