Responses private-to-public output_index projection

Chose applying every Responses event, including response-side item_reference, to authoritative private state before suppression and limit checks over filtering references first, because lifecycle reconciliation, retained-state accounting, and terminal shorthand resolution require complete coordinates. Build public output through an exact private-to-visible map and require streamed IDs to match terminal indices. Never forward reference lifecycle events or log reference IDs. Resolve shorthand only to one completed private item; fail closed with sanitized response.failed and output: [] on incomplete, ambiguous, colliding, overflowing, or coordinate-shifting references.