sx delivered most of the foundation since the plan was written: alias
re-exports instead of pub, the modules/std.sx facade barrel, and native
std fs/process/json/cli/hash/log/test/socket/mem. Replace the 'sx
Foundation Work' section with as-built status + remaining gaps, mark
Phase 0 done / Phase 1 partial, note the superseded subplan-01 slices,
and drop the retired flow-harness execution contract (subplan 08, roles,
checkpoint files).
