rseng-legacy-code

# Working with legacy research code Research software outlives its authors' contracts. The typical legacy situation is a working but untested codebase whose author has left, whose behavior IS the specification, and whose results current papers still depend on. The prime directive: preserve today's behavior first, improve structure second, change behavior only deliberately and visibly. In research code a silent behavior change is worse than a crash - it can corrupt published results downstream. ## First contact with an inherited codebase Before changing anything: 1. Get it running. Capture the exact environment that works (versions, OS, data paths) in a lockfile or container while it still runs anywhere (rseng-reproducible-environments) - the running environment is itself endangered knowledge. 2. Snapshot everything: commit the code as-is to version control, including generated files and local tweaks, before any cleanup (rseng-version-control-review). Tag it as the reference state. 3. Recover intent from what exists: papers that used the code, commit messages, variable names, comments in any language, old emails or READMEs. Write down what you learn as documentation NOW (rseng-documentation) - you are the next person who will forget. 4. Map the danger zones: which outputs feed publications, which parts are dead code, which parts everyone fears. Effort goes where published results depend on correctness. ## Characterization tests: the safety ne...