The board cache should recognize positions that differ only by a supported rotation or reflection. Implement a canonical representation that treats those positions consistently without changing the original board.
Build the implementation in Rust 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 is a nonempty square list of strings. Consider four quarter-turn rotations of the board and of its horizontal reflection (reverse each row). Return the lexicographically smallest list of row strings among these eight forms. Characters compare using Unicode order. Reject empty or nonsquare boards.
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.