Codex+Opus ship-gate: a <=64KB but deeply-nested JSON manifest makes json.loads raise
RecursionError, which escaped _read_manifest_urls into the app-shell route -> every page
load 503s. Add RecursionError to the fail-safe except + regression test (verified
red-without/green-with). Co-authored-by: santastabber <santastabber@users.noreply.github.com>