refactor(status-manager): delete empty entries

- if we settle and there's no additional entries for a key, delete it instead
  of setting to an empty array
- ensure  always return 'No unsettled entry' error instead of sometimes 'key not found'

packages/fast-usdc/src/exos/status-manager.js

@@ -92,7 +92,7 @@ export const prepareStatusManager = zone => {
     );
   };
 
-  return zone.exo(
+  const statusManager = zone.exo(
     'Fast USDC Status Manager',
     M.interface('StatusManagerI', {
       advance: M.call(CctpTxEvidenceShape).returns(M.undefined()),
@@ -148,35 +148,39 @@ export const prepareStatusManager = zone => {
        * @throws {Error} if a pending settlement was not found for the address + amount
        */
       settle(address, amount) {
-        const key = makePendingTxKey(address, amount);
-        const pending = pendingTxs.get(key);
-
+        const pending = statusManager.lookupPending(address, amount);
         if (!pending.length) {
-          throw makeError(`No unsettled entry for ${q(key)}`);
+          throw makeError(`No unsettled entry for ${q([address, amount])}`);
         }
 
         const pendingCopy = [...pending];
         pendingCopy.shift();
         // TODO, vstorage update for `TxStatus.Settled`
-        pendingTxs.set(key, harden(pendingCopy));
+
+        const key = makePendingTxKey(address, amount);
+        if (pendingCopy.length) {
+          return pendingTxs.set(key, harden(pendingCopy));
+        }
+        return pendingTxs.delete(key);
       },
 
       /**
-       * Lookup all pending entries for a given address and amount
+       * Lookup all pending entries for a given address and amount.
        *
        * @param {NobleAddress} address
        * @param {bigint} amount
-       * @returns {PendingTx[]}
+       * @returns {PendingTx[]} pendingTxs or empty array if nothing is found
        */
       lookupPending(address, amount) {
         const key = makePendingTxKey(address, amount);
         if (!pendingTxs.has(key)) {
-          throw makeError(`Key ${q(key)} not yet observed`);
+          return harden([]);
         }
         return pendingTxs.get(key);
       },
     },
   );
+  return statusManager;
 };
 harden(prepareStatusManager);
 

packages/fast-usdc/test/exos/status-manager.test.ts

@@ -87,7 +87,7 @@ test('cannot SETTLE without an ADVANCED or OBSERVED entry', t => {
       statusManager.settle(evidence.tx.forwardingAddress, evidence.tx.amount),
     {
       message:
-        'key "pendingTx:[\\"noble1x0ydg69dh6fqvr27xjvp6maqmrldam6yfelqkd\\",\\"150000000\\"]" not found in collection "PendingTxs"',
+        'No unsettled entry for ["noble1x0ydg69dh6fqvr27xjvp6maqmrldam6yfelqkd","[150000000n]"]',
     },
   );
 });
@@ -139,19 +139,17 @@ test('settle SETTLES first matched entry', t => {
       statusManager.settle(evidence.tx.forwardingAddress, evidence.tx.amount),
     {
       message:
-        'No unsettled entry for "pendingTx:[\\"noble1x0ydg69dh6fqvr27xjvp6maqmrldam6yfelqkd\\",\\"150000000\\"]"',
+        'No unsettled entry for ["noble1x0ydg69dh6fqvr27xjvp6maqmrldam6yfelqkd","[150000000n]"]',
     },
     'No more matches to settle',
   );
 });
 
-test('lookup throws when presented a key it has not seen', t => {
+test('lookingPending returns an empty array when presented a key it has not seen', t => {
   const zone = provideDurableZone('status-test');
   const statusManager = prepareStatusManager(zone.subZone('status-manager'));
 
-  t.throws(() => statusManager.lookupPending('noble123', 1n), {
-    message: 'Key "pendingTx:[\\"noble123\\",\\"1\\"]" not yet observed',
-  });
+  t.deepEqual(statusManager.lookupPending('noble123', 1n), []);
 });
 
 test('StatusManagerKey logic handles addresses with hyphens', async t => {