feat(arap)!: documents read their figures from standing lines; control accounts

refuse hand entries (P4b S1, part A)

Plan P4b (D-45), slice S1, the engine half: rules.md B-38.

- ledger-core: every receivables or payables line carries its document
  (Ledger.line_docs: DocRef, Movement, DocTag), written by the document
  commands in the step that posts it, derived on replay from the existing
  document events (the role's account as it stood then; payments by the
  ordinal rule), copied onto a reversal's mirror. Ledger::stands_on;
  doc_state / invoice_state / bill_state (total, paid, outstanding,
  status Open/Partial/Paid/WrittenOff/Void, overdue days) as of any day;
  ar_aging / ap_aging read them, so reversed payments and voids are right.
  The control guard (add_line, add_line_fx, post_entry,
  register_recurring) refuses untagged lines on receivables/payables,
  exempting a reversal's mirror of a legacy line; replay never refuses.
  Bounds (kernel::running_bounds, bounds_kept) on payments and reversals;
  a document reversal never dated before its entry; deposit/payer accounts
  must be cash-like and hold no role. New API: receive_payment_with /
  pay_bill_with (PaymentDetails: instrument, reference), void_document /
  check_void_document, control_check, payments_recorded,
  standing_payments, replay_reverse_entry. Invoice.amount_paid/status
  remain only as derived caches for the MCP layer until part B.
  cashflow bill_splits reads payments from the tags.
- ledger-store: journal feature document_standing (D-39 gated) for a
  payment accepted only because an earlier one was reversed;
  receive_payment_with / pay_bill_with (instrument journaled as
  entry.instrument_set, reference in the description), void_document;
  replay uses replay_reverse_entry; schema 15 drops the projection's
  amount_paid/status. Fixture p4-arap-before + golden figures written by
  the version before S1, adjudicated in arap_standing.rs.
- ledger-gui: party card, cash "coming up" and company owed totals read
  doc_state as of today (late from the derived state).
- Lean Documents.lean (control_agrees and friends); Kani
  bounds_check_matches_definition,
bounds_kept_is_the_definition_on_books_in_bounds;
  rules B-38, B-18/B-23 amended; bookspec `older = true` for legacy hand
  lines; tests that hand-post to 1200/2000 post as replay or renumbered.

Review fixes (both reviews of part A):
- control_role_of guards only an account the role is assigned to or one
  holding its documents' lines (a chart's own 1200 Equipment or card at
  2000 is free until a document posts there); payment accounts check
  other roles by holds_role (type-checked). The MCP tests that failed on
  the guard (oracle_mcp, spec_projects) pass unchanged.
- standing_payments leaves out reversals (sorted, deduped); replayed
  tags match the movement's side; payments_recorded counts every payment
  event (tagged or not, Ledger.payment_events) and refuses overflow.
- The record caches settled (paid + discounted + written off) and owed
  (Invoice/Bill.owed, never serialized): a void never reads as paid.
- assign_role: receivables/payables refuse moving onto an account with
  untagged lines (RoleAccountHasHandLines) and, on their control account
  holding a balance, say DocumentRoleHoldsBalance (no hand entry named);
  B-23 reworded. The reversal-mirror exemption only takes a hand line
  off (even chain depth); putting it back is refused.
- DocStatus Overpaid and Unattached; aging leaves out credit balances;
  ControlCheck.attention lists out-of-bounds and unattached documents.
- stands_on counts a chain in order; indexes (doc_index, doc_accounts,
  order_pos, reversed_by) keep the derived figures linear.
- Viewer reads a post-dated document as of its own date; one state per
  row. bounds_kept's side-crossing documented as intended.
- Tests: ten new spec_documents scenarios, stronger proptests, store
  proptest arap_props (live = replay = snapshot at every date, closed
  months), fuzz ops void/payments with details, a GUI post-dated test;
  Lean Step.assign / Step.release with unattached_zero kept; model
  limits stated in docs/testing.md and B-38.
Review fixes (CPA and engineering lenses): only an assigned role's
account or one holding document lines is a control account (a chart's
own 1200 asset stays free); a role can't move onto untagged lines or off
document lines (Lean Step.assign); a void's cache never reads as paid;
no Decimal sum panics; per-document indexes keep figures linear; a
replayed tag matches its side; the feature gate counts payment events;
a payment's reversal is never listed as standing; an overpaid document
has its own status; the viewer keeps post-dated documents.

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

crates/ledger-core/src/cashflow.rs

@@ -1030,7 +1030,8 @@ type KindOrder = (u8, u8, String);
 /// that part, equipment first, to its payables lines and to its payments,
 /// so the payment is an investing outflow (ASC 230-10-45-13(c)). A bill
 /// posts to the general-expenses control today, so this is empty until a
-/// bill can carry an equipment line.
+/// bill can carry an equipment line (P4b S4). A bill's payments are the
+/// entries whose payables line carries it (rules.md B-38).
 #[derive(Default)]
 struct BillSplits {
     /// By (entry, line index): the investing part of that payables line,
@@ -1077,15 +1078,20 @@ fn bill_splits(roles: &Roles<'_>, chains: &Chains) -> Result<BillSplits, LedgerE
                 left -= part;
             }
         }
-        // Each payment pays the equipment part first, as the bill records
-        // them, in order: the part its payables carried (none when the
-        // payable is financing: its payments are repayments already).
-        // A payment's own amount bounds what it paid of this bill. A
-        // reversed payment still counts against what later payments carry
-        // (the bill keeps it as paid), but not against what is unpaid at a
-        // period's end after the reversal.
+        // Each payment pays the equipment part first, in the order paid:
+        // the part its payables carried (none when the payable is
+        // financing: its payments are repayments already). A payment's
+        // own amount bounds what it paid of this bill. A reversed payment
+        // paid nothing for good: its reversal unpays it on the reversal's
+        // date, and it leaves the equipment part for the payment that
+        // stands (P4b.2 gap 6: it used to keep it, as the bill did).
         let mut owed = equipment - left;
-        for &(pay, amount) in ledger.bill_payments(bill.id) {
+        let payments = ledger
+            .doc_lines(crate::DocRef::Bill(bill.id))
+            .into_iter()
+            .filter(|l| l.movement == crate::Movement::Payment && !l.reversal);
+        for pl in payments {
+            let (pay, amount) = (pl.entry, -pl.amount);
             let Some(p) = ledger.get_entry(pay) else {
                 continue;
             };
@@ -1111,7 +1117,9 @@ fn bill_splits(roles: &Roles<'_>, chains: &Chains) -> Result<BillSplits, LedgerE
                         undo = -undo;
                         cur = r;
                     }
-                    owed -= part;
+                    if ledger.in_effect(p.id()) {
+                        owed -= part;
+                    }
                     this -= part;
                 }
             }