Restack on the carved-out foundation (#192), per review feedback on #170.
The seam files resolve to the carve-out's revision — its prompt-order
neutrality fix (backends no longer inject 'tools'; the structured runtime
gates its own capture-tool registration) restores the subagent tools to
master's front position, so every recorded fixture is re-recorded on the
stacked tree and the authored error-finish/cancel headers re-patched to the
stacked tool list ([subagent, subagent_fork, workflow, todo_write, ...]).