js-tcp-reno-congestion-control
Done. The problem (/workspace/problem.json) had no scaffold or graded harness present, so I implemented the TCP Reno state machine from scratch, verified it three independent ways, and wrote the self-contained solution document.
/workspace)SOLUTION.md — the requested markdown: title, root-cause analysis, the exact fix (full code + usage + commands), and a verification section.solution.js — RenoCongestionControl class; RFC 5681 classic Reno. node --check clean, runs on Node 20/22 (plain stdlib, nothing to install).verify.js — the verification harness (reproducible, fixed-seed PRNG).cwnd >= ssthresh after the SS increment.ssthresh = max(floor(cwnd/2), 2·MSS), cwnd = ssthresh + 3·MSS); every later dup — including #3+ while in FR — inflates cwnd += MSS.recover high-water mark: partial → deflate to ssthresh, stay in recovery; full (ack >= recover) → exit to CA with cwnd = ssthresh.k·MSS (SS) / k·MSS²/cwnd (CA).cwnd = MSS, halve ssthresh (floor to 2·MSS), reset dup counter + recover, double RTO.ssthresh identical on every step; cwnd identical outside CA; within < MSS in CA.cwnd ≥ MSS, ssthresh ≥ 2·MSS, finite, valid state): zero violations.All three files are in place and the harness exits 0.
# Evidence - Problem class: js-tcp-reno-congestion-control - Model: openrouter/deepseek/deepseek-v4-flash-0731 - Solved: 2026-08-28T11:09:02.117Z - Verification: solution produced by pi in sandbox; see signatures.json
{"description": "Implement the TCP Reno congestion-control state machine: process a chronological event stream of cumulative ACKs, duplicate ACKs, and RTO timeouts, updating cwnd and ssthresh through slow start (cwnd += MSS per new ACK), congestion avoidance (cwnd += MSS*MSS/cwnd), fast retransmit with fast recovery on 3 duplicate ACKs (ssthresh = max(cwnd/2, 2*MSS), cwnd = ssthresh + 3*MSS, inflate by MSS per further dup-ACK, deflate on partial ACK), and timeout (ssthresh = max(cwnd/2, 2*MSS), cwnd = MSS, exponential backoff). Emit the (cwnd, ssthresh, state) trajectory after every event. Scoring compares your trajectory against a reference implementation on randomized traces with out-of-order delivery, ACK gaps, and timeouts landing mid-recovery.", "environment": "node20", "language": "js", "model": "openrouter/deepseek/deepseek-v4-flash-0731", "problem_class": "js-tcp-reno-congestion-control", "provider": "openrouter", "solved_at": "2026-08-28T11:09:02.118Z", "version": "20"}