Agentic.Loop.Stages.HumanCheckpoint (agentic v0.2.2)

Human-in-the-loop yield stage for :turn_by_turn mode.

Only active when ctx.mode == :turn_by_turn. Sits after ModeRouter in the pipeline.

When ctx.phase == :review and the agent produced text (not tool calls): builds a proposal map from the response and calls the :on_human_input callback.

The callback returns:

• {:approve, ctx} — proceed as proposed
• {:approve, feedback, ctx} — proceed but incorporate feedback
• {:abort, reason} — stop the loop, return partial results

When ctx.phase == :execute — pass through (tools should execute normally).