feat: invoices and bills take a project, line by line (B-37 item 8)

A client project's invoiced revenue and a contractor's billed cost could
never count toward the project: books.create_invoice and books.create_bill
posted at once with untagged lines, and only a draft's line takes a class.
Job costing (B-37 item 3) collects a job's billings and the supplier
invoices for its direct costs on its cost sheet, so each document line
now takes an optional project.

The owner decided it on 2026-10-22 (plan D-43, rules.md B-37 item 8):
each line takes one project or none; a document spanning N projects is N
lines, each with its own amount; no percentage split, so every figure is
exact; a cost truly shared among projects names none on the document
and reaches projects only as entries of their own under the company's
monthly allocation convention, when books.conventions has one (otherwise
it stays untagged and the agent asks the human). The reasoning, stated
in B-37: job costing charges a job the costs traceable to it, whole, and
reaches shared costs only by allocation on a stated basis. ASC
340-40-25-7 counts as directly related both the costs traceable to a
contract (25-7(a), (b), (d), (e)) and allocations of costs that relate
directly to it (25-7(c)); 25-8 expenses general and administrative cost.
The books carry the first whole on the document's line and the second as
the allocation convention's own entries; neither is a percentage on the
document (sources/fasb-asc.md, 25-7 and 25-8 added). The handbook's
projects rule and the line's class parameter say the same, and no
handbook sentence lets a shared cost be split across a document's lines.

The accounting: the document's entry posts one revenue (an invoice's) or
expense (a bill's) line per project its lines name, in the order each is
first named, each the sum of that project's lines, and the untagged
lines' sum as one more line (arap::document_parts, conservation checked
by a proptest). A document naming no project therefore posts exactly the
one line every document posted before. The receivable or payable line is
never tagged: it is a balance-sheet line, which item 3 counts nothing;
the payments (receive_payment, pay_bill) move cash against it and take no
project either. Nothing but the projects moves: the P&L, the 1099
worksheet (payments made, B-19) and party totals (what moved the money,
B-35) read the same with or without the tags (twin-books test); the
projects with the untagged lines still partition the P&L.

- ledger-core: DocumentLine.class_id (serde-omitted when none, so old
  documents serialize as before); create_invoice / create_bill split the
  revenue or expense side by project and tag it; an unknown project is
  refused whole (atomically).
- ledger-store: a document line's project is journaled as class_id on
  invoice.created / bill.created, and the entry's line as
  entry.line_class_set right after its entry.line_added (the entry.posted
  lines carry class_id, as a hand-built entry's do). Behind a NEW journal
  feature, document_line_projects (KNOWN_FEATURES, declared by new books,
  asked for before the first journaled line, not even the control
  accounts written on refusal); not `projects`, which the live books
  already declared: the owner consents again at the next upgrade. A
  malformed class_id is corrupt; null or absent is none. Untagged
  documents journal byte for byte as before; old journals replay
  unchanged.
- ledger-mcp: each line takes class (id or name, resolved like
  add_line's, every one before anything is written); the result gains
  notes for a finished or abandoned project, and on an invoice for an
  on-spec project (is there now an agreement? on spec a hoped-for
  payment is no receivable, B-37 item 4), tagged anyway; books lacking
  the feature refuse with format_upgrade_pending. books.get_entry shows a
  line's class_id and project. The handbook's "an invoice or bill takes no
  project yet" caveat now depends on the books: gone where the feature is
  declared, an "until their format upgrade" note where it isn't.
- ledger-gui: an invoice's or bill's page (its entry's) lists the
  document's lines, each project a link that opens it; the demo's client
  invoices are tagged to "Client work", whose snapshot is now its revenue
  less its contractors. Looking at the page in a narrow window found a
  tagged line's tag pushing the amounts past the pane (any tagged entry):
  the name is now cut to leave the tag room, the tag itself at most half
  the cell.
- bookspec: an `invoice` event, and `lines` with `project` on a bill or
  an invoice; example projects-invoice-and-bill-lines-count-by-project,
  worked by hand, both projects client work (Zeta 3,500.00 - 1,200.00 =
  2,300.00; Harbor 200.00;
  untagged -1,750.00; together the P&L's 750.00; Dana's 1099 payments
  1,250.00).
- fuzz: fuzz_store_replay can declare journal features.
- Tests: core, store, MCP, viewer, the P2-served cutover fixture and a
  viewer/server parity test (its month lists the same length, not
  empty); a tagged document's reversal nets its projects to zero, live
  and replayed; books.get_entry's class_id; the handbook served as a
  resource both ways; each fix broken to confirm its test fails
  (docs/testing.md). Docs: rules.md B-27 and B-37 items 3 and 8,
  sources/fasb-asc.md, plan/served.md D-43,
  mcp-interface.md, testing.md, parity.md, plan/STATUS.md.

No proof changed (no kernel arithmetic: document_parts sums with the
existing document_total).

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

crates/ledger-gui/src/pages/cash.rs

@@ -663,6 +663,7 @@ mod tests {
             vec![DocumentLine {
                 description: "work".into(),
                 amount: cents(c),
+                class_id: None,
             }]
         };
         let acme = b.s.add_customer("Acme").unwrap();

crates/ledger-gui/src/pages/company.rs

@@ -802,6 +802,7 @@ mod tests {
             vec![DocumentLine {
                 description: "work".into(),
                 amount: cents(c),
+                class_id: None,
             }]
         };
         let acme = b.s.add_customer("Acme").unwrap();

crates/ledger-gui/src/pages/entry.rs

@@ -10,6 +10,7 @@ use crate::theme::{self, pal};
 use crate::widgets;
 use egui::{CornerRadius, Margin, RichText, Stroke, Ui, vec2};
 use egui_phosphor::regular as icon;
+use ledger_core::arap::DocumentLine;
 use ledger_core::{EntryStatus, Side};
 use ledger_store::Attachment;
 use rust_decimal::Decimal;
@@ -231,26 +232,18 @@ pub fn detail(ui: &mut Ui, b: &Books, e: &EntryInfo, shell: &mut Shell<'_>) {
                             ui.allocate_ui(vec2(w, 22.0), |ui| {
                                 ui.set_width(w);
                                 ui.horizontal(|ui| {
-                                    let r = widgets::link_truncated(
-                                        ui,
-                                        RichText::new(b.account_label(line.account))
-                                            .font(theme::regular(13.5)),
-                                    );
+                                    let tag = project_tag(line.class_id, &class_names);
+                                    let (r, project) = name_and_tag(ui, tag.as_ref(), |ui| {
+                                        widgets::link_truncated(
+                                            ui,
+                                            RichText::new(b.account_label(line.account))
+                                                .font(theme::regular(13.5)),
+                                        )
+                                    });
                                     if r.clicked() {
                                         shell.go(Route::Account(line.account));
                                     }
-                                    if let Some((cid, c)) = line
-                                        .class_id
-                                        .and_then(|c| class_names.get(&c).map(|n| (c, n)))
-                                        && widgets::link(
-                                            ui,
-                                            RichText::new(format!("{} {c}", icon::TAG))
-                                                .font(theme::regular(11.5))
-                                                .color(p.muted),
-                                        )
-                                        .on_hover_text("Open this project")
-                                        .clicked()
-                                    {
+                                    if let Some(cid) = project {
                                         shell.go(Route::Project(cid));
                                     }
                                     if let (Some(cur), Some(fa)) =
@@ -308,6 +301,14 @@ pub fn detail(ui: &mut Ui, b: &Books, e: &EntryInfo, shell: &mut Shell<'_>) {
                 });
             ui.add_space(18.0);
 
+            // The invoice or bill it records: its lines as the document
+            // gives them, each project a link (rules.md B-37 item 8).
+            if let Some(doc) = document_of(b, e.id) {
+                section(ui, &doc.title);
+                document_lines(ui, &doc, &class_names, total_w, amt_w, shell);
+                ui.add_space(18.0);
+            }
+
             // Receipts and documents: filed on it, linked to it, or linked
             // to the invoice, bill, or payroll run it records; a withdrawn
             // receipt filed on it stays, marked.
@@ -406,6 +407,144 @@ pub fn detail(ui: &mut Ui, b: &Books, e: &EntryInfo, shell: &mut Shell<'_>) {
         });
 }
 
+/// The invoice or bill an entry records: its name and due date, and its
+/// lines.
+pub struct DocumentOf<'a> {
+    /// "Invoice 3, due Oct 1, 2026".
+    pub title: String,
+    /// Its lines, as journaled.
+    pub lines: &'a [DocumentLine],
+}
+
+/// The invoice or bill whose entry is `entry`, if it records one.
+pub fn document_of(b: &Books, entry: ledger_core::EntryId) -> Option<DocumentOf<'_>> {
+    let due = |what: &str, id: u64, due: chrono::NaiveDate| {
+        format!("{what} {id}, due {}", fmt::date(due))
+    };
+    b.ledger
+        .invoices()
+        .into_iter()
+        .find(|i| i.entry_id == entry)
+        .map(|i| DocumentOf {
+            title: due("Invoice", i.id, i.due_date),
+            lines: &i.lines,
+        })
+        .or_else(|| {
+            b.ledger
+                .bills()
+                .into_iter()
+                .find(|x| x.entry_id == entry)
+                .map(|x| DocumentOf {
+                    title: due("Bill", x.id, x.due_date),
+                    lines: &x.lines,
+                })
+        })
+}
+
+/// A document's lines: each description, its project (a link that opens
+/// it), and its amount.
+fn document_lines(
+    ui: &mut Ui,
+    doc: &DocumentOf<'_>,
+    class_names: &std::collections::HashMap<u32, String>,
+    total_w: f32,
+    amt_w: f32,
+    shell: &mut Shell<'_>,
+) {
+    let p = pal(ui.ctx());
+    egui::Frame::new()
+        .stroke(Stroke::new(1.0, p.border))
+        .corner_radius(CornerRadius::same(10))
+        .inner_margin(Margin::symmetric(12, 8))
+        .show(ui, |ui| {
+            ui.set_width(total_w - 26.0);
+            ui.horizontal(|ui| {
+                let w = ui.available_width() - amt_w - 8.0;
+                let (r, _) = ui.allocate_exact_size(vec2(w, 18.0), egui::Sense::hover());
+                ui.painter().text(
+                    r.left_center(),
+                    egui::Align2::LEFT_CENTER,
+                    "Line",
+                    theme::regular(12.0),
+                    p.muted,
+                );
+                widgets::amount_cell(ui, "Amount", amt_w, p.muted, false, false);
+            });
+            for line in doc.lines {
+                ui.horizontal(|ui| {
+                    let w = ui.available_width() - amt_w - 8.0;
+                    ui.allocate_ui(vec2(w, 22.0), |ui| {
+                        ui.set_width(w);
+                        ui.horizontal(|ui| {
+                            let tag = project_tag(line.class_id, class_names);
+                            let (_, project) = name_and_tag(ui, tag.as_ref(), |ui| {
+                                ui.add(
+                                    egui::Label::new(
+                                        RichText::new(&line.description).font(theme::regular(13.5)),
+                                    )
+                                    .truncate(),
+                                )
+                            });
+                            if let Some(cid) = project {
+                                shell.go(Route::Project(cid));
+                            }
+                        });
+                    });
+                    widgets::amount_cell(ui, &fmt::money(line.amount), amt_w, p.text, false, false);
+                });
+            }
+        });
+}
+
+/// A line's project tag: its id and the text it shows.
+fn project_tag(
+    class: Option<u32>,
+    class_names: &std::collections::HashMap<u32, String>,
+) -> Option<(u32, String)> {
+    let c = class?;
+    class_names
+        .get(&c)
+        .map(|n| (c, format!("{} {n}", icon::TAG)))
+}
+
+/// `name` (a truncating label), then `tag` as a link that opens its
+/// project: the project, when clicked. The tag's width (at most half the
+/// cell, cut with an ellipsis past it) is kept back from the name, so a
+/// tagged line never grows past its cell.
+fn name_and_tag(
+    ui: &mut Ui,
+    tag: Option<&(u32, String)>,
+    name: impl FnOnce(&mut Ui) -> egui::Response,
+) -> (egui::Response, Option<u32>) {
+    let p = pal(ui.ctx());
+    let avail = ui.available_width();
+    let gap = ui.spacing().item_spacing.x;
+    let tag_w = tag.map_or(0.0, |(_, t)| {
+        ui.painter()
+            .layout_no_wrap(t.clone(), theme::regular(11.5), p.muted)
+            .size()
+            .x
+            .min(avail / 2.0)
+    });
+    let room = if tag.is_some() { tag_w + gap } else { 0.0 };
+    let r = ui
+        .allocate_ui(vec2((avail - room).max(0.0), 22.0), name)
+        .inner;
+    let go = tag.and_then(|(cid, t)| {
+        ui.allocate_ui(vec2(tag_w, 22.0), |ui| {
+            widgets::link_truncated(
+                ui,
+                RichText::new(t).font(theme::regular(11.5)).color(p.muted),
+            )
+        })
+        .inner
+        .on_hover_text("Open this project")
+        .clicked()
+        .then_some(*cid)
+    });
+    (r, go)
+}
+
 pub fn section(ui: &mut Ui, title: &str) {
     let p = pal(ui.ctx());
     ui.label(
@@ -588,7 +727,66 @@ pub fn share_text(
 #[cfg(test)]
 mod tests {
     use super::*;
-    use crate::test_support::{Build, d, find, old_books, render};
+    use crate::test_support::{Build, d, find, old_books, render, render_at};
+
+    /// A tagged line keeps its project tag inside its cell, in a narrow
+    /// pane too: the name is cut to leave the tag room, so the amounts
+    /// stay in their columns (an invoice's revenue line and its document
+    /// line, each tagged; rules.md B-37 item 8).
+    #[test]
+    fn a_tagged_line_keeps_its_amounts_in_their_column() {
+        use ledger_core::arap::DocumentLine;
+        let mut b = Build::new("entry-tag-room");
+        let project =
+            b.s.add_project(
+                "A project with a rather long name indeed",
+                &ledger_core::ProjectFacts::default(),
+            )
+            .unwrap();
+        b.s.add_account(
+            "4000",
+            "Revenue from design services and consulting",
+            ledger_core::AccountType::Revenue,
+            None,
+            false,
+        )
+        .unwrap();
+        let c = b.s.add_customer("Cedar").unwrap();
+        let inv =
+            b.s.create_invoice(
+                c,
+                d(2026, 3, 2),
+                d(2026, 4, 1),
+                vec![DocumentLine {
+                    description: "Brand identity, website and a long tail of revisions".into(),
+                    amount: Decimal::new(123_456, 2),
+                    class_id: Some(project),
+                }],
+            )
+            .unwrap();
+        let entry = b.s.ledger().get_invoice(inv).unwrap().entry_id;
+        let (_dir, books) = b.books();
+        let texts = render_at(books, Route::Entry(entry), 1000.0);
+        // The amount: the receivable's debit, the revenue's credit, both
+        // totals, the document line's; every one ends at a column's edge,
+        // the credits at one, the debits at another.
+        let pane = find(&texts, "LINES").pos.x;
+        let mut edges: Vec<i32> = texts
+            .iter()
+            .filter(|t| t.text == fmt::money(Decimal::new(123_456, 2)) && t.pos.x > pane)
+            .map(|t| (t.pos.x + t.width).round() as i32)
+            .collect();
+        assert_eq!(edges.len(), 5, "{edges:?}");
+        edges.sort_unstable();
+        edges.dedup();
+        assert_eq!(
+            edges.len(),
+            2,
+            "the debit column and the credit column: {edges:?}"
+        );
+        let tag = format!("{} A project with a rather long name indeed", icon::TAG);
+        assert_eq!(texts.iter().filter(|t| t.text == tag).count(), 2);
+    }
 
     /// An entry's totals line: "Balanced" when its debits equal its
     /// credits, "Out of balance" when they don't, "Too large to total"

crates/ledger-gui/src/pages/parties.rs

@@ -1709,6 +1709,7 @@ mod tests {
             vec![DocumentLine {
                 description: "work".into(),
                 amount: cents(c),
+                class_id: None,
             }]
         };
         // Owed, not yet due; owed, due today; paid, past due; owed, past

crates/ledger-gui/src/pages/profit.rs

@@ -448,6 +448,7 @@ mod tests {
             vec![DocumentLine {
                 description: "work".into(),
                 amount: cents(c),
+                class_id: None,
             }]
         };
         let acme = b.s.add_customer("Acme").unwrap();