fork·watch

A browser-native Bitcoin fork and stale-block monitor in the spirit of ForkMonitor — but with no server and no trusted nodes. Chain tips are observed from many independent witnesses, every header is re-verified locally (proof-of-work, linkage, cumulative work), and forks, reorgs and stale blocks are recorded with the evidence kept.

A sibling of block·health, built on the same stack: the vendored bitcoin-kernel engine, NIP-333 header streams, and the canonical WebRTC mesh library.

How it watches

Three classes of witness feed one fork-aware header tree:

1. Nostr publishers — NIP-333 kind-33333 events (newest 12 headers per event), any number of publisher keys. The publisher is a filter, not an authority.
2. Esplora explorers — mempool.space and blockstream.info tips, headers fetched and verified per block. Explorers are dumb byte sources; a wrong answer convicts itself.
3. Mesh peers — block·health browsers advertise their self-verified header-chain tips over WebRTC; fork·watch joins the same rooms as a silent witness (?peer=wss://…&room=…, same link format as health). Every browser in the room is an independent observer with its own network position.

What it records

• Stale blocks / reorgs — when the best tip moves to a non-descendant, the displaced arm is marked stale and kept forever. The stale arm is the observation.
• Chain splits — two children under one parent, while both arms are live.
• Witness divergence — a source whose tip is not on the locally-verified best chain.
• Invalid headers — a witness offering a header that fails its own proof-of-work.
• Height lies — a witness claiming a height the parent linkage contradicts.
• Slow blocks — an hour without a block, for context.

Events persist in localStorage and survive reloads. The header tree prunes deep linear history but never prunes stale blocks or fork points.

What it deliberately does not do (yet)

ForkMonitor's multi-implementation invalid-block detection and per-block inflation checks need real full nodes with UTXO sets — out of reach of header-level monitoring. The roadmap (shared with block·health) closes some of the gap: full-block archival of stale blocks at the moment they die, snapshot-based validation, and publishing signed fork-event notes back to nostr so browsers become a decentralized alert network.

Layout

index.html       the app: witnesses, detection, timeline UI
header-tree.js   fork-aware header DAG: PoW-checked inserts, work-weighed best tip,
                 stale marking, evidence-preserving pruning
peer-source.js   block·health mesh peer (same wire protocol), vendored from health
                 plus an any-peer fetch extension: tips + headers as witnesses, and
                 scanned blocks pulled from peers' caches before falling back to esplora
webrtc-mesh.js   vendored verbatim from bitcoin-kernel/health (the canonical copy):
                 mesh-hello instance dedupe, peer/attempt caps, keep-oldest connections
engine/          vendored bitcoin-kernel codec + JSON-LD consensus schemas
tests/           node test suite (regtest chains, real PoW)

Run locally

python3 -m http.server 8900    # then open http://localhost:8900/
node tests/test-header-tree.mjs

No build step, no backend — static files on GitHub Pages.