Code Katas

Attempt these tasks before opening feedback. Preserve initial predictions, diffs, commands, actual results and assistance. Reuse valid lab evidence; extra lesson drills are repair or optional depth.

P16: Exercise mixed clients

Interleave old/new Grid reads and writes, including overwrites, empty strings and invalid coordinates.

P17: Trace acknowledgement loss

Have the selected provider record a write then time out. Explain why automatic fallback is dangerous.

P18: Plan state migration

Sketch replacing the grid dictionary with a persisted store. Name backfill, concurrent-write and old-reader obligations.

P19: Design rollback and retirement

Distinguish routing rollback, schema recovery, compensation and roll-forward in a migration note.

P20: Separate a repair

After refactoring, propose aggregate rather than per-line invoice rounding. Preserve the original trace and write changed expectations separately.

Use the behavior contracts and offline labs. For a named gap, consult the Refactoring book index and module reading guide.