The Eden webapp uses a subchain to track history. This subchain contains a subset of eosio blocks relevant to the Eden contract's history. eden-micro-chain.wasm, which runs in both nodejs and in browsers, produces and consumes this subchain. It answers GraphQL queries about the contract history. Here's a typical setup:
+--------+ +----------+ +------+ +----------+ +-----------+
| dfuse | => | Relevant | => | wasm | => | subchain | => | websocket |
| client | | History | | | | blocks | | |
+--------+ +----------+ | | +----------+ +-----------+
| | +----------+ +-----------+
| | => | current | => | http GET |
| | | state | | |
+------+ +----------+ +-----------+
+-----------+ +----------+ +------+ +----------+ +--------+
| websocket | => | subchain | => | wasm | <= | GraphQL | <= | client |
| | | blocks | | | | Query | | code |
+-----------+ +----------+ | | +----------+ | |
+-----------+ +----------+ | | +----------+ | |
| http GET | => | initial | => | | => | GraphQL | => | |
| | | state | | | | Response | | |
+-----------+ +----------+ +------+ +----------+ +--------+
When a client starts up, it fetches a copy of eden-micro-chain.wasm and a copy of the most-recent state from the Box server. It then subscribes to block updates through a websocket connection.
https://genesis.eden.eoscommunity.org/ uses https://box.prod.eoscommunity.org . Third parties may host apps which also use https://box.prod.eoscommunity.org to gain access to Eden history.
Third parties may also host their own box server instances. The box server sources live at https://github.com/eoscommunity/Eden/tree/main/packages/box . The box container is available as ghcr.io/eoscommunity/eden-box:<git commit>, https://github.com/eoscommunity/Eden/pkgs/container/eden-box .