Read the case study correctly
GitHub's account of migrating a Copilot runtime to Rust with Copilot is interesting because it shows a real engineering team using an assistant inside a consequential codebase. It should not be read as proof that a model can own a migration. The value lies in how the team constrained, reviewed, and validated the work.
Protect the invariants first
Before changing implementation language, document compatibility requirements, latency targets, memory limits, observability hooks, and rollback triggers. Use the assistant to explore localized changes, generate tests, or explain unfamiliar code; do not let it silently redefine what must remain true.
Make review evidence explicit
Require benchmarks, failure-mode tests, and a diff that a maintainer can reason about. A migration is complete only when the operating behavior is understood, not when the compiler is satisfied.