Dependency graph

Handlers can declare dependencies on other handlers by name:

lastcall.register(
  'database',
  async () => {
    await db.disconnect();
  },
  { phase: 'cleanup' },
);

lastcall.register(
  'api',
  async () => {
    await api.close();
  },
  { phase: 'cleanup', deps: ['database'] },
);

api will not start until database completes.

Parallel execution

Independent handlers run in parallel within the same dependency wave:

lastcall.register('redis', async () => {}, { deps: [] });
lastcall.register('cache', async () => {}, { deps: [] });
lastcall.register('app', async () => {}, { deps: ['redis', 'cache'] });

Wave 1: redis + cache (parallel)
Wave 2: app

Circular dependencies

Circular deps throw at execution time:

Handler "a" depends on "b" which depends on "a"
→ TopologicalSortError

Cross-phase dependencies

Dependencies only apply within the same phase. Registering a cross-phase dependency throws immediately — including when the dependent handler was registered first.

Phases still run in order (pre → drain → cleanup → post), so use phase assignment instead of cross-phase deps.