P3: odd cents split the same running way everywhere (defect 17, D-38)

Members' shares of earnings are split cumulatively by largest remainder in
the closes, the members' equity statement, the K-1 worksheet and the
viewer, so a member's capital on a given day never moves by a cent when its
month is later closed. Old closes replay as they were; the first P3 close
carries any true-up. Feature members_cumulative. Kani and Lean proofs of
the bounded drift; bookspec examples.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01T3gXMVt7XJPi6ens1or9Dj

crates/ledger-store/tests/fixtures/old-books-writer/src/bin/members.rs

@@ -0,0 +1,83 @@
+//! x_member_closes: members closes under each rounding rule main wrote
+//! (P3 review R-2), through MAIN's Store API (main 00226a4c, 2026-10-20).
+//! Two members, A and B, 50/50; A has a distributions account. Eleven
+//! months, each closed in order:
+//!   Jan-Mar: untagged (the last member absorbs): +0.01, -0.03, +0.05;
+//!            A's 1.00 distribution in February is swept into A's capital.
+//!   Apr-Jun: "largest_remainder" (each close on its own): +0.07, -0.01, +0.03.
+//!   Jul-Nov: "cumulative" (the run rule), broken by a close to retained
+//!            earnings in September: +0.01, +0.01, (RE +0.01), +0.03, -0.05.
+//! Hand-computed: A's earnings 0.07, B's 0.05 (of 0.12 closed to them;
+//! exact 0.06 each); retained earnings 0.01.
+use chrono::NaiveDate;
+use ledger_core::*;
+use ledger_store::Store;
+use rust_decimal::Decimal;
+
+fn d(m: u32, day: u32) -> NaiveDate {
+    NaiveDate::from_ymd_opt(2026, m, day).unwrap()
+}
+fn usd(s: &str) -> Money {
+    Money::new(s.parse::<Decimal>().unwrap(), Currency::USD)
+}
+
+fn main() {
+    let dir = std::path::PathBuf::from(std::env::args().nth(1).unwrap()).join("x_member_closes");
+    let _ = std::fs::remove_dir_all(&dir);
+    std::fs::create_dir_all(&dir).unwrap();
+    let mut s = Store::create(&dir, Currency::USD).unwrap();
+    let cash = s.add_account("1000", "Cash", AccountType::Asset, None, false).unwrap();
+    let cap_a = s.add_account("3000", "Capital A", AccountType::Equity, None, false).unwrap();
+    let cap_b = s.add_account("3001", "Capital B", AccountType::Equity, None, false).unwrap();
+    let dist_a = s.add_account("3100", "Distributions A", AccountType::Equity, None, false).unwrap();
+    let rev = s.add_account("4000", "Sales", AccountType::Revenue, None, false).unwrap();
+    let exp = s.add_account("6000", "Fees", AccountType::Expense, None, false).unwrap();
+    let post = |s: &mut Store, date, dr, cr, amount: &str| {
+        let e = s.create_entry(date, "x").unwrap();
+        s.add_line(e, dr, Side::Debit, usd(amount)).unwrap();
+        s.add_line(e, cr, Side::Credit, usd(amount)).unwrap();
+        s.post_entry(e).unwrap();
+    };
+    post(&mut s, d(1, 2), cash, cap_a, "100.00");
+    post(&mut s, d(1, 2), cash, cap_b, "100.00");
+    post(&mut s, d(2, 20), dist_a, cash, "1.00");
+    let members = vec![
+        MemberClose { capital: cap_a, share: "0.5".parse().unwrap(), distributions: Some(dist_a) },
+        MemberClose { capital: cap_b, share: "0.5".parse().unwrap(), distributions: None },
+    ];
+    let months: [(u32, &str, &str); 11] = [
+        (1, "0.01", "last"),
+        (2, "-0.03", "last"),
+        (3, "0.05", "last"),
+        (4, "0.07", "per"),
+        (5, "-0.01", "per"),
+        (6, "0.03", "per"),
+        (7, "0.01", "run"),
+        (8, "0.01", "run"),
+        (9, "0.01", "re"),
+        (10, "0.03", "run"),
+        (11, "-0.05", "run"),
+    ];
+    for (m, net, rule) in months {
+        match net.strip_prefix('-') {
+            Some(loss) => post(&mut s, d(m, 10), exp, cash, loss),
+            None => post(&mut s, d(m, 10), cash, rev, net),
+        }
+        let end = NaiveDate::from_ymd_opt(2026, m + 1, 1).unwrap().pred_opt().unwrap();
+        let p = s.create_period(&format!("2026-{m:02}"), d(m, 1), end).unwrap();
+        let to = match rule {
+            "last" => CloseTo::MembersLastAbsorbs(members.clone()),
+            "per" => CloseTo::MembersPerClose(members.clone()),
+            "run" => CloseTo::Members(members.clone()),
+            _ => CloseTo::RetainedEarnings { sweep: vec![] },
+        };
+        s.close_period_to(p, &to).unwrap();
+    }
+    let bal = |id| s.ledger().account_balance(id).unwrap();
+    println!(
+        "WROTE x_member_closes: A {} B {} dist {}",
+        bal(cap_a),
+        bal(cap_b),
+        bal(dist_a)
+    );
+}