Document LLM actuator tool return semantics

[Copilot]

LLM actuator tools acknowledge queue acceptance, not completed railway actions. This adds a critical analysis of the deferred execution path and its observability gaps.

• LLM-facing results

  • Documents exact queued ... responses for request_route, release_route, and approve_train.
  • Separates synchronous validation and backpressure errors from later simulation outcomes.

• Deferred actuation

  • Maps tool invocation through ActuatorCommandQueue, DispatchDecisionApplier, and actuator ports.
  • Identifies outcomes logged but not returned to the initiating tool call.

• Operational assessment

  • Covers stale approval-cap observations, uncorrelated snapshot feedback, and stateless dispatch-cycle limitations.
  • Proposes an asynchronous, correlated outcome channel and simulation-thread admission-cap enforcement.

request_route(...) → "queued request_route ..."
                   → later: Reserved | AllPathsBlocked | Conflict | NoRouteExists
                   → currently logged, not returned to the LLM

• Fixes Investigation actuators tools return values #819

[bedaHovorka]

done, no merge