books.renumber_account: give an account a new code, history kept

Ledger::renumber_account changes only the code (entries name accounts by
id): refuses an unknown account, a blank or used code, and a control code
for an account of the wrong type or a placeholder. Journaled as
account.renumbered (with the previous code), replayed, projected, shown
in the viewer's journal. The MCP tool lists wanderbooks.toml settings
that still name the old code. The server instructions now warn that the
engine can't tell a same-type account with another purpose at a control
code (a hosting expense at payroll's 6100).

Tests: core property (only the code changes; trial balance equal), core
refusals, the store's command property, MCP end to end with restart.
Mutation on the new code: 8 of 8 viable caught.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01GWVo7x3UHw5kwCUaWxiejX

crates/ledger-store/src/store.rs

@@ -2062,6 +2062,26 @@ impl Store {
         Ok(out)
     }
 
+    /// Give an account a new code (see `Ledger::renumber_account`).
+    /// Journaled as `account.renumbered`, with the code it had.
+    pub fn renumber_account(&mut self, account: AccountId, code: &str) -> Result<(), StoreError> {
+        self.rehearse(|l| l.renumber_account(account, code))?;
+        self.ledger.check_renumber_account(account, code)?;
+        let previous = self
+            .ledger
+            .chart()
+            .get(account)
+            .map(|a| a.code.clone())
+            .unwrap_or_default();
+        let line = self.append_journal(
+            "account.renumbered",
+            json!({"account_id": account, "code": code, "previous_code": previous}),
+        )?;
+        self.ledger.renumber_account(account, code)?;
+        apply_line_to_sqlite(&self.conn, &line)?;
+        Ok(())
+    }
+
     /// Set (or clear) an account's tax category and deductible percent.
     /// Journaled as `account.tax_set`.
     pub fn set_account_tax(
@@ -3251,6 +3271,9 @@ pub(crate) fn replay_line_into_ledger(
                 p.get("vendor_id").and_then(|v| v.as_u64()),
             )?;
         }
+        "account.renumbered" => {
+            ledger.renumber_account(get_u64(p, "account_id")?, get_str(p, "code")?)?;
+        }
         "account.tax_set" => {
             let pct = match p.get("deductible_percent").and_then(|v| v.as_str()) {
                 Some(s) => Some(s.parse().map_err(|_| {
@@ -3795,6 +3818,12 @@ fn apply_line_rows(conn: &Connection, line: &JournalLine) -> Result<(), StoreErr
                 )?;
             }
         },
+        "account.renumbered" => {
+            conn.execute(
+                "UPDATE accounts SET code = ? WHERE id = ?",
+                params![get_str(p, "code")?, get_u64(p, "account_id")? as i64],
+            )?;
+        }
         "account.tax_set" => {
             conn.execute(
                 "UPDATE accounts SET tax_category = ?, deductible_percent = ? WHERE id = ?",