refactor(mcp): the party_id, document_id and cash_account aliases are removed (P5)

Agent reason: one name for one thing. S4 and S6 kept the old spellings "until
P5" so an agent that learned them did not break; P5 removes them, so the
schema an agent reads has one parameter for each fact and a call cannot name
the same thing twice with different answers.

books.create_invoice takes customer and books.create_bill vendor (a record's
id, its party's id or its name; required), no party_id.
books.receive_payment and books.pay_bill take invoice or bill and
deposit_to or paid_from, no document_id or cash_account; a payment names its
document and its account or is refused saying which to pass. A number that is
one record's id and another's name is still refused, never guessed (INVARIANT
6).

The over-the-wire tests that used the old spellings now use the new
(document_id becomes invoice or bill, cash_account becomes deposit_to or
paid_from, party_id becomes customer or vendor given as the id's text); the
one test that named the alias, party_id_alias_still_works, is now
a_customer_by_id_and_by_name_is_one_record and checks the same two spellings
of a customer, by id and by name, name one record.

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

crates/ledger-mcp/src/tools/documents.rs

@@ -455,17 +455,7 @@ impl BooksServer {
     ) -> Result<Json<InvoiceOut>, String> {
         let p = params.0;
         let mut store = self.lock()?;
-        let customer = match (&p.customer, p.party_id) {
-            (Some(c), None) => c.trim().to_string(),
-            (None, Some(id)) => id.to_string(),
-            (Some(c), Some(id)) if c.trim() == id.to_string() => c.trim().to_string(),
-            (Some(_), Some(_)) => {
-                return Err("give the customer once: customer or party_id, not both".into());
-            }
-            (None, None) => {
-                return Err("give customer: a customer id, a party id or a name".into());
-            }
-        };
+        let customer = p.customer.trim().to_string();
         let customer_id = resolve_customer(&store, &customer)?;
         let date = parse_date(&p.date)?;
         let lines = document_lines(&store, p.lines)?;
@@ -606,17 +596,7 @@ impl BooksServer {
     ) -> Result<Json<BillOut>, String> {
         let p = params.0;
         let mut store = self.lock()?;
-        let vendor = match (&p.vendor, p.party_id) {
-            (Some(v), None) => v.trim().to_string(),
-            (None, Some(id)) => id.to_string(),
-            (Some(v), Some(id)) if v.trim() == id.to_string() => v.trim().to_string(),
-            (Some(_), Some(_)) => {
-                return Err("give the vendor once: vendor or party_id, not both".into());
-            }
-            (None, None) => {
-                return Err("give vendor: a vendor id, a party id or a name".into());
-            }
-        };
+        let vendor = p.vendor.trim().to_string();
         let vendor_id = resolve_vendor_arg(&store, &vendor)?;
         let date = parse_date(&p.date)?;
         let received_on = p.received_on.as_deref().map(parse_date).transpose()?;