merge: P4b S5, sent tracking (branch S5, ad649be3)

The second of the paused branches. invoice.sent, Ledger::mark_sent (with
its Lean step), books.mark_sent in its own group, the two attention
items, schema 17. Conflicts, resolved as plan 8.0.2 says: the shared
over-the-wire test file crates/ledger-cli/tests/documents.rs (S4.4's
file kept whole, S5's test appended, its create call given the
confirmed: true the S4.4 contract now needs), types.rs (both appends
kept), docs/parity.md (the review's oracle row and S5's new row).

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01HS8WZziDnyxunC23MUxrLp

crates/ledger-cli/tests/documents.rs

@@ -709,3 +709,89 @@ fn an_invoice_bill_to_uses_the_billing_details() {
     assert_eq!(bill_to["phone"], "555-0100", "{bill_to}");
     assert_eq!(bill_to["shipping_address"], "Gate 2", "{bill_to}");
 }
+
+// P4b S5: sent tracking (merged from branch S5).
+
+/// Two sends on one invoice: the first the original (defaults: the
+/// token's name, email, today's company day), the second a reminder with
+/// the channel's message id; then `books.documents` shows the last send
+/// and `books.document` the whole record.
+#[test]
+fn mark_sent_records_who_and_how() {
+    let books = common::Books::new("p4b-s5-mark-sent");
+    let mut wire = books.session("p4b-s5");
+    let customer =
+        common::answer_of(&wire.call("books.add_customer", json!({"name": "Fernhill Labs"})))
+            .unwrap()["id"]
+            .as_u64()
+            .unwrap();
+    let invoice = common::answer_of(&wire.call(
+        "books.create_invoice",
+        json!({"party_id": customer, "date": "2026-03-01", "due_date": "2026-03-31",
+               "lines": [{"description": "Design", "amount": "1200.00"}], "confirmed": true}),
+    ))
+    .unwrap()["id"]
+        .as_u64()
+        .unwrap();
+
+    let first = common::answer_of(&wire.call(
+        "books.mark_sent",
+        json!({"invoice": format!("invoice:{invoice}"), "on": "2026-03-05",
+               "by": "Avery Quill", "recipients": ["billing@fernhill.example"]}),
+    ))
+    .unwrap();
+    assert_eq!(first["invoice"], json!(format!("invoice:{invoice}")));
+    assert_eq!(first["sends"][0]["on"], json!("2026-03-05"));
+    assert_eq!(first["sends"][0]["by"], json!("Avery Quill"));
+    assert_eq!(
+        first["sends"][0]["via"],
+        json!("email"),
+        "the default channel"
+    );
+    assert_eq!(first["sends"][0]["to"], json!(["billing@fernhill.example"]));
+    assert_eq!(
+        first["sends"][0]["kind"],
+        json!("original"),
+        "the first send is the original"
+    );
+
+    // The second names no `by`, `via` or `kind`: this session's token
+    // (the agent), email, and a reminder now that one send is recorded.
+    let second = common::answer_of(&wire.call(
+        "books.mark_sent",
+        json!({"invoice": invoice.to_string(), "on": "2026-03-20",
+               "recipients": ["billing@fernhill.example"], "reference": "msg-2",
+               "note": "Second copy"}),
+    ))
+    .unwrap();
+    let sends = second["sends"].as_array().unwrap();
+    assert_eq!(sends.len(), 2, "{second}");
+    assert_eq!(sends[1]["by"], json!("test"), "the token's name");
+    assert_eq!(sends[1]["via"], json!("email"));
+    assert_eq!(sends[1]["kind"], json!("reminder"));
+    assert_eq!(sends[1]["reference"], json!("msg-2"));
+    assert_eq!(sends[1]["note"], json!("Second copy"));
+
+    let listed =
+        common::answer_of(&wire.call("books.documents", json!({"kind": "invoices"}))).unwrap();
+    assert_eq!(
+        listed["documents"][0]["ref"],
+        json!(format!("invoice:{invoice}"))
+    );
+    assert_eq!(
+        listed["documents"][0]["last_sent"],
+        json!("2026-03-20"),
+        "the list shows the latest send"
+    );
+    let one = common::answer_of(&wire.call(
+        "books.document",
+        json!({"ref": format!("invoice:{invoice}"), "as_of": "2026-03-31"}),
+    ))
+    .unwrap();
+    assert_eq!(one["sends"].as_array().unwrap().len(), 2);
+    assert_eq!(
+        one["outstanding"],
+        json!("1200.00"),
+        "a send changes no figure"
+    );
+}