fix(spring): host ExecutorService beans break A2AAutoConfiguration startup #96

Problem

dev.openan.workflow.engine.spring.A2AAutoConfiguration declares the A2A server executor with a bare @ConditionalOnMissingBean:

@Bean(destroyMethod = "shutdownNow")
@ConditionalOnMissingBean
public ExecutorService agentExecutorPool(A2AProperties properties) { ... }

With no attributes the condition matches by return type (ExecutorService). Host applications routinely define their own executor beans - dispatchers, ScheduledExecutorService-based SSE heartbeat schedulers, pub-sub workers (ScheduledExecutorService is a subtype, so it is a candidate too). Because user configuration is registered before auto-configuration, any single one of them suppresses agentExecutorPool.

requestHandler (parameter 5) and restHandler then inject ExecutorService by type, without a qualifier, so the application fails to start:

UnsatisfiedDependencyException: Error creating bean with name 'requestHandler'
... parameter 5 ... NoUniqueBeanDefinitionException: expected single matching bean
but found 3: spaceAiDispatcherExecutor,spaceSseHeartbeatScheduler,spaceSsePubSubExecutor

The parameter-name hint in that message is a red herring: the parameter is named pool and no bean of that name exists.

Expected

The starter's own executor should be created and used regardless of unrelated ExecutorService beans in the host, while a host can still override it explicitly.

Fix

1. Match by bean name: @Bean(name = "agentExecutorPool", destroyMethod = "shutdownNow") plus @ConditionalOnMissingBean(name = "agentExecutorPool").
2. Qualify both injection points: @Qualifier("agentExecutorPool") on the requestHandler and restHandler ExecutorService parameters.

Both halves are required: without (1) the pool is never created, without (2) the injection stays ambiguous.

Workaround before the fix

Declare a @Primary ExecutorService bean in the host with the same settings.