The cache must evict the least recently used entry when it reaches capacity. Implement the operation log so reads and overwrites update recency in the specified way.
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 has positive integer capacity and operations put (key,value), get (key), or delete (key). A successful get or put makes the key most recent; missing get returns null without changing order. Put beyond capacity evicts the least recent key. Delete missing keys is a no-op. Return gets and final keys from least to most recent. Reject invalid capacity or unknown operations.
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.