fix(account-tree): preserve accounts on validation errors

Cache the last successful account query result and use it when
validation errors occur. This prevents the account tree from
showing "No accounts found" when the ledger has balance assertion
or other validation errors.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

Author: robcohen

src/account-tree.js

@@ -22,6 +22,9 @@ let treeVersion = 0;
 /** @type {Map<string, boolean>} Track expanded state across updates */
 const expandedState = new Map();
 
+/** @type {Array<{account: string, balance: {amount: number, currency: string}}>} Cache last successful account data */
+let cachedAccounts = [];
+
 // Account type colors matching charts.js
 const accountColors = {
     Assets: '#22d3ee', // cyan
@@ -365,12 +368,14 @@ function triggerRerender(container) {
  * @returns {Promise<Array<{account: string, balance: {amount: number, currency: string}}>>}
  */
 async function queryAccountBalances(source) {
-    if (!isWasmReady()) return [];
+    if (!isWasmReady()) return cachedAccounts;
 
     try {
         const result = await executeQuery(source, 'BALANCES');
-        if (!result || result.error || !result.rows || result.rows.length === 0) {
-            return [];
+        if (!result || !result.rows || result.rows.length === 0) {
+            // Query returned no rows - return cached data if available
+            // This handles cases where validation errors prevent querying
+            return cachedAccounts;
         }
 
         // BALANCES returns: account, balance (or similar columns)
@@ -408,10 +413,13 @@ async function queryAccountBalances(source) {
             }
         }
 
+        // Cache successful result
+        cachedAccounts = accounts;
         return accounts;
     } catch (err) {
         console.error('Account tree query error:', err);
-        return [];
+        // Return cached data on error
+        return cachedAccounts;
     }
 }
 
@@ -468,6 +476,7 @@ export function clearAccountTree() {
     }
     treeVersion = 0;
     currentGetSource = null;
+    cachedAccounts = [];
     // Don't clear expandedState to preserve user preferences across sessions
 }