test(sync): wait for watcher handlers to register in SIGHUP cache test

"reloads sync config when SIGHUP is received" flaked on the Node 22 CI
job with TypeError: handlers[0] is not a function, because the fixed-50
rounds of flushWatchSetup() occasionally return before chokidar's
dynamic-import + FS-sweep chain reaches watcher.on('change', ...).

Add a bounded wait-until-registered loop (max 10 extra flushes) and a
length assertion so the test either succeeds or fails loudly with a
clear diagnostic, instead of the misleading TypeError. The sibling
"three ticks" test at line 1027 already has an implicit barrier
(expect(handlers.length).toBeGreaterThan(0)) which is why it has not
flaked.

Author: sjsyrek

tests/unit/sync/sync-command.test.ts

@@ -1076,6 +1076,14 @@ describe('SyncCommand', () => {
 
         const runPromise = command.run({ watch: true, debounce: 50 } as CliSyncOptions);
         await flushWatchSetup();
+        // Under CI worker contention the fixed-round flush occasionally
+        // returns before watcher.on('change', ...) has registered. Loop
+        // flushWatchSetup with a hard ceiling so we fail loudly rather than
+        // with the misleading "handlers[0] is not a function".
+        for (let i = 0; i < 10 && handlers.length === 0; i++) {
+          await flushWatchSetup();
+        }
+        expect(handlers.length).toBeGreaterThan(0);
 
         const initialLoads = mockLoadSyncConfig.mock.calls.length;