Workspace Strategy vocabulary for Subagents and Workflow steps.

A Workspace Strategy describes how a child sees files and whether writes can mutate the parent workspace. Subagents execute shared and isolated, and may opt in to virtual_overlay with operator-owned read-set context. Workflow steps also support explicit virtual commands. Each invocation imports host files afresh and returns an unapplied virtual_diff; only commands within that invocation share virtual edits. Canonical Logs/artifacts persist on disk; no persistent Session scratch is implied.