`src/capabilities.rs` — the capability traits

Nine small traits, one per optional engine component, so code can depend on “has detection” without depending on the whole bundle. LoopManagers implements all of them.

Key items

Trait	Method	Returns
`Observable`	`observers()`	`&ObserverHost`
`Detectable`	`detection()`	`&DetectionManager`
`FallbackCapable`	`fallback()`	`&FallbackManager`
`Compactable`	`context_manager()`	`Option<&Arc<ContextManager>>`
`RememberCapable`	`memory()`	`Option<&Arc<dyn LoopMemory>>`
`StreamCapable` [streaming]	`stream_handler()`	`&StreamHandler` — never None (passthrough default)
`Hookable` [hooks]	`hook_executor()`	`Option<&HookExecutor>`
`PipelineAware`	`pipeline()`	`Option<&ToolPipeline>`
`HealthTrackable` [tool_health]	`health_registry()`	`Option<&ToolHealthRegistry>`

Behavior notes

The Option returns encode “not configured” — the engine checks and skips cleanly. StreamCapable is the exception: it substitutes a no-resilience passthrough, so “is a real handler set?” is not answerable through the accessor.
Generic code should narrow to the traits it needs (fn foo(b: &impl Detectable)) — that’s the entire point of this module.

Deep dive: Managers.