BEAM-native Avatar actor with typed actions and bounded tool execution.

Avatar asks a typed actor predictor for one action per turn. Tool results, including policy denials and execution errors, become structured observations for the next turn. A reserved Finish action or iteration exhaustion invokes a separate typed finalizer for the task signature.

Each tool callback runs in its own unlinked task, bounded by :tool_timeout_ms (default 30 seconds), that takes no place in the task pool. The task carries the caller's settings, Imp.Run context and Imp.Deadline, and ends when the caller does, so a tool stops when its caller is killed, when its run is cancelled and when the run's owner dies. A tool that crashes, or whose task exits, is an observation, not the caller's crash. When the caller works on a place in the pool, a stream of Imp tasks the tool enumerates (Imp.Predict.Parallel.map/3, Imp.Evaluate.run/2) runs on that place, one item at a time; an Imp.Tasks.async/1 the tool starts itself waits for a place of its own, so with a full pool it waits until the tool times out. A timeout kills the task, records a terminal action observation and proceeds directly to finalization. A timed-out call and one whose task exited read as :unknown in Imp.Tool.outcome/1, since the tool may have acted.

Inside a run, each tool call is recorded as a :tool_call event and a :tool_result event whose metadata.outcome says how it ended. Avatar does not ask a run's :authorize callback, so a run started with one refuses an Avatar program ({:execution_capability_unsupported, Imp.Predict.Avatar, :authorization}).