Rotating numbered log archives can overwrite a file if the rename order is wrong. Produce a safe deterministic plan that follows the configured retention rule.
Build the implementation in Bash under /app, with /app/run.sh as its entry point. Read one JSON request from standard input and write one JSON result to standard output. Input has base filename without slashes, nonnegative integer keep and distinct filenames. The active base becomes base.1; existing base.N for canonical positive integer N becomes base.(N+1), except N>=keep is deleted. For keep zero, delete active and all numbered archives. Ignore unrelated names and noncanonical suffixes such as .01. Return moves in descending source suffix order (active last), and sorted delete names. Reject invalid base, duplicate filenames or invalid keep. No filesystem changes are performed.
Reject inputs that violate an explicit validation rule with exit status 2, no standard output, and {"error":"invalid_input"} on standard error. For valid input, exit with status 0. Keep the implementation reusable for new inputs; it must work offline and must not depend on the example data being the only data it receives.
Repair or replace the unfinished /app/run.sh and add source files under /app. Malformed JSON must use the same invalid-input response. Do not read /tests or /oracle from the application.