The storage simulator allocates contiguous extents using first-fit placement. Finish allocation and release behavior so fragmented free space is handled without overlapping live allocations.
Build the implementation in C 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 free half-open integer intervals [start,end] and positive integer requests. Free intervals must be nonnegative and nonempty without overlap; sort them and merge adjacent intervals. Process requests in order, using the first interval large enough and allocating from its left edge. Failed requests return null without mutation. Return starts and remaining free intervals. Reject invalid extents, overlaps or boolean/noninteger/nonpositive request sizes.
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.