Six commits from wilm-import: the squashed import, route documentation, the
channel remap onto our tag-and-trunk model, the project map, parallel test
support, and the four smaller review findings.
Merged rather than cherry-picked: the published mirror rewrites hashes, so the
commits do not apply one at a time against our history even though the squashed
diff applies clean.
Scope: product
# Conflicts:
# docs/PROJECT-MAP.md
b5540e631c