awaitTravel

Drive the integration loop for handle to completion (or cancellation). Suspends. Returns the final TravelResult.

Each step:

• If handle.isCanceled is true, break.

• If handle.destination differs from the current direction target (set by TravelHandle.redirect), re-plan from the current position.

• Compute step distance min(stepSize, remaining), delay by stepDist / velocity, advance position by that step.

• If within ε of the destination, snap exactly and mark complete.

The agent's position is updated via ContinuousProjection.moveTo at each step, so concurrent spatial queries see the agent moving. Distances and directions are measured by the projection, so on a torus the agent goes the short way round, as with travelTo.