feat(arap): a write-off on the timeline, and the CPA's note (P4b S7)

The viewer's invoice page already drew a WriteOff movement; now the
fixture proves it: a written-off invoice reads Written off, owes nothing,
and its timeline's "Written off" row opens the entry (the screenshot
invoice-written-off).

Needs attention gains the one item the tax rule asks for: a write-off
made this calendar year is listed, one per invoice, as "Write-off
awaiting the CPA's note", with what was written off, the day, and the
prompt that opens the document. Whether a debt is worthless, and in
which year, is a tax judgment that stays with the CPA (plan 8.3.16); the
books flag it and keep the evidence beside it until the year ends. The
item is computed in ledger-package's one attention function, so the
viewer and books.start see it alike; view_model.rs compares the two reads
on the same books.

The handbook's invoices-and-bills section starts here (S4.5 adds the
issue, terms and payment steps around it): step 4 says when to void, to
write off, or to reverse, and the recovery procedures D-49 records — the
same year, reverse the write-off and record the payment; a later year, a
plain entry to a bad-debt-recoveries revenue account, the invoice staying
written off (IRC §111).

Tests: a_write_off_shows_on_the_timeline,
a_write_off_is_flagged_for_the_cpa.

crates/ledger-gui/tests/invoices.rs

@@ -208,3 +208,58 @@ fn books_without_documents_show_no_overview_tiles_for_them() {
     shot(&mut h, "receivables-empty");
     assert!(h.query_by_label("No invoices").is_some());
 }
+
+/// A written-off invoice (plan P4b S7): $500 issued, written off whole for
+/// a bad debt with its evidence, so it reads Written off owing nothing.
+fn write_off_books(dir: &TempDir) -> (u64, u64) {
+    let mut s = Store::create(&dir.0.join("books-data"), Currency::USD).unwrap();
+    s.add_account("1000", "Checking", AccountType::Asset, None, false)
+        .unwrap();
+    s.add_account("3000", "Capital", AccountType::Equity, None, false)
+        .unwrap();
+    let client = s.add_customer("Harbor Client").unwrap();
+    let inv = s
+        .create_invoice(
+            client,
+            d(2026, 2, 1),
+            d(2026, 3, 1),
+            vec![line("Consulting", 50_000)],
+        )
+        .unwrap();
+    let (entry, _) = s
+        .write_off_invoice(
+            inv,
+            d(2026, 3, 10),
+            Decimal::new(50_000, 2),
+            "collection exhausted",
+            Some(ledger_store::WriteOffEvidence::File {
+                file_name: "collection-letter.pdf",
+                mime_type: "application/pdf",
+                bytes: b"%PDF-1.4\nFinal demand\n%%EOF\n",
+                description: Some("Collection attempts"),
+            }),
+        )
+        .unwrap();
+    (inv, entry)
+}
+
+/// The write-off is on its invoice's timeline, reads "Written off", and
+/// opens its entry.
+#[test]
+fn a_write_off_shows_on_the_timeline() {
+    let dir = TempDir::new("write-off");
+    let (inv, entry) = write_off_books(&dir);
+    let mut h = open(&dir, Route::Invoice(inv));
+    shot(&mut h, "invoice-written-off");
+    assert!(
+        h.query_by_label_contains("Written off, entry #")
+            .is_some(),
+        "the timeline shows the write-off"
+    );
+    // The status chip reads its label ("Written off"), not "late".
+    assert!(h.query_by_label("Written off").is_some());
+    h.get_by_label_contains(&format!("Written off, entry #{entry},"))
+        .click();
+    h.run_steps(2);
+    assert_eq!(h.state_mut().route(), &Route::Entry(entry));
+}