implement: sync main and cut task-<NNNN>-<slug> before work, with
stop-and-ask guards for a dirty tree, a diverged main, and an unmerged
blocker. Replaces the no-commit rule with one commit, a push, and a PR
carrying the review's Risk block plus any unaddressed findings.
test-driven-development: every test is written by a general-purpose
sub-agent that never reads the implementation; the main agent writes the
code and never edits a test.
