09
strangler fig
Grow a new skin around the old system, take it over piece by piece, let the old wood die. No big-bang rewrite.
What is strangler fig?
A strangler fig wraps the old system: routing sends some requests to new code, and the old code is retired in pieces.
Why does strangler fig matter when vibe coding?
The model offers to rewrite the directory. On legacy code that is a disaster. A strangler replaces one entry at a time, with characterization tests holding the rest.
How do you do strangler fig?
Pick one entry — a route, a button. Put a switch in front, pointing at the new implementation. Run both. Shift traffic. Delete the old. Pick the next entry.
How do you ask a model for strangler fig?
Strangle (entry). Do not rewrite the module. Add a switch so old and new both run. Tests lock old behaviour.
What goes wrong with strangler fig?
A dual-write switch that never comes down. Old and new both live forever. The fig does not strangle. It tangles.