The reconciliation code removes every occurrence of a value even when the request only removes some copies. Repair it so the remaining collection reflects the requested multiplicities.
Build the implementation in Ruby 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 available and remove lists of strings. Consume one available occurrence per removal value, ignoring excess removals. Return surviving available values in their original order; removal consumes earliest occurrences. Reject nonstring items.
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.