For the Autonomi team: WebRTC Direct endpoints that browsers cannot reach

From the BNR / skaists.dev team, 2026-10-06. Ready for upstream review. We
have not touched ant-node and do not plan to; this is evidence, not a patch.

The finding

Across the first two independent networks, 365/365 commonly settled
endpoints agreed in outcome. A fixed 40-endpoint cohort checked again about
35 minutes later from three execution vantage points kept its baseline
phenotype in 93/93 settled observations: 43/43 dead stayed dead and 50/50
live stayed open. Two non-cohort endpoints showed cross-network disagreement
in the broader window, so we do not claim network effects are impossible.
The evidence points strongly to endpoint-specific reachability state,
without yet identifying the mechanism.

The numbers

Browser: Chromium, the published @withautonomi/ant-browser-sdk 0.1.1 (window 3:
0.1.2), reading one public 214 MB file (try_autonomi.mp4) for 150 s per run.

• Window 1: 375 endpoints seen by both; 365 settled on both; 195 dead from
  both, 170 open from both, 0 opposite. All 195 never reached ICE-connected,
  on any attempt, from either network.
• Window 2, all three vantage points: 259 settled on all three; 127 dead
  from all, 130 open from all, 2 differ (both outside the cohort).
• Roughly half of the settled endpoints a browser dials are unreachable from
  a browser, and almost every failed attempt fails before ICE connects.

What we do and do not claim

• We claim: whether a browser can open one of these endpoints depends on the
  endpoint, not on the browser's network, for this sample.
• We do not claim a cause. "Never reached ICE-connected" localises the
  failure to connection setup; it does not tell a closed UDP port from a NAT
  mapping, a firewall, a listener that is down, a stale advertisement or a
  wrong address/port.
• What the code does (read at release v0.21.0 and main
  d41a353;
  the function is identical in both): advertised_addr() returns an explicit
  advertised_addr, else a bound specific IP, else the first non-relay native
  address of the same family with the WebRTC listener's local port.
  refresh_browser_endpoint() publishes that into the DHT
  (L731–L764).
  We found no reachability check of that socket before publication; the
  listener snapshot itself notes "no external probe is implied" (L520). ant-client
  already records that "a third to a half" of mainnet WebRTC Direct endpoints
  time out when dialled
  (wasm_transport.rs).
  So advertised_addr() is a good place to look; our data does not prove the
  defect is there.

Matching our endpoints to yours

Endpoint IDs in our receipts are the first 16 hex characters of
SHA-256 of "ip:port" (for example SHA-256("203.0.113.7:10001")). They are
pseudonymous, not anonymous: with the advertised endpoint set you can
recompute them and see exactly which nodes are in the dead-from-every-network
group. Raw addresses are not published.

Reproduce it

• Receipts: two-network ·
  cohort
• Recorder (wraps RTCPeerConnection, records dial → ICE → DTLS → channel →
  answer per attempt): surfaces/ant-transport.js
• Probe, one run on whatever network it is on:
  e2e/ant-reach-probe.mjs
• Runner probes: .github/workflows/ant-reach.yml
  (runs 37525604244 and 37529869576 carry the raw exports as artifacts)
• Compare and cohort: scripts/ant-reach-compare.mjs ·
  scripts/ant-reach-cohort.mjs

Update 2026-10-07: current SDK, and 24 hours

• SDK 0.1.2 (2026-10-05) fixes two WebKit-only problems (ant-client feat(replication): stop penalising a peer for not holding a close-group chunk #215,
  feat(storage): replace the LMDB chunk store with one file per chunk, and migrate onto it #216; feat(storage): replace the LMDB chunk store with one file per chunk, and migrate onto it #216 notes Chromium "never lost a connection"). Our runs are Chromium,
  so they do not explain these results. Window 3 ran on 0.1.2 from all three
  vantage points: 147 endpoints settled on all three; 73 dead from all, 73
  open from all, 1 differs.
• The fixed 40-endpoint cohort over ten runs in about 24 hours (SDK 0.1.1 and
  0.1.2): the 20 dead endpoints stayed dead in 108/108 settled
  observations; the 20 live ones stayed open in 126/128. Both misses are
  one endpoint (09d7e457307accd9), dead from one runner and open from the
  other at the same moment: network effects are real for some endpoints, just
  not for the dead group.
• Receipt: cohort, 24 h.

Update 2026-10-08: cohort closed

• Across 17 runs over about 34 hours (SDK 0.1.1, then 0.1.2), the 20 dead
  endpoints stayed dead in 159/159 settled observations and the 20 live
  ones stayed open in 203/205; both misses are the same single endpoint.
• Final window (2026-10-08 06:24Z), laptop vs GitHub Linux runner: 285
  endpoints settled on both; 148 dead from both (147 never ICE-connected on
  any attempt), 137 open from both, 0 opposite.
• Receipt: final cohort.
  The scheduled probe is stopped; the workflow and probe stay available on demand.