The router needs the longest matching path prefix, measured in path segments. Finish dispatch so a route for one segment does not accidentally match a longer segment with the same text prefix.
Build the implementation in Go 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 routes mapping absolute POSIX path prefixes to handler strings and paths to dispatch. Valid paths are / or slash-prefixed nonempty components, with no trailing slash, empty components, dot, dot-dot or backslash. Match only exact prefixes or whole-segment ancestors; / matches everything. Return the longest matching handler or null per path. Reject invalid route or request paths.
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.