# `Musubi.Transport.Channel`
[🔗](https://github.com/fahchen/musubi/blob/v0.3.0/lib/musubi/transport/channel.ex#L1)

Generic Phoenix Channel adapter that mounts any Musubi root store named in
the channel module's allowlist.

The public client API connects to a root by `{module, id}` (see
`docs/client-contract.md`). `topic` is an internal transport detail:
the client builds an opaque topic of the form `"musubi:<opaque_ref>"` and
carries the requested `module`, `id`, and optional `params` in the channel
join payload.

## Mounting in a Phoenix endpoint

    defmodule MyAppWeb.MusubiChannel do
      use Musubi.Transport.Channel,
        stores: [
          MyApp.Stores.CartPageStore,
          MyApp.Stores.InboxStore
        ]
    end

    defmodule MyAppWeb.UserSocket do
      use Phoenix.Socket

      channel "musubi:*", MyAppWeb.MusubiChannel

      def connect(_params, socket, _connect_info), do: {:ok, socket}
      def id(_socket), do: nil
    end

## Join payload

Incoming join payload:

    %{
      "module" => "MyApp.Stores.CartPageStore",
      "id" => "cart:current-user",
      "params" => %{...optional...}
    }

The channel rejects joins whose `module` is not in the configured allowlist.

## Lifecycle

On `join/3` the adapter starts a fresh `Musubi.Page.Server` for the resolved
root module + params and links it to the channel pid. On channel
`terminate/2` the adapter unlinks the page server and stops it with the
channel's terminate reason. Reconnect is recovery (BDR-0015): each new
join builds a fresh page server with `version: 1` and an initial
`replace ""` envelope.

## Wire shape

Incoming `"command"` payload:

    %{"store_id" => ["filters"], "name" => "change_query", "payload" => %{...}}

`store_id` is the in-tree path-shaped locator for the addressed store node.
Root is `[]`.

Outgoing `"patch"` payload — `Musubi.Page.PatchEnvelope.to_wire/1`:

    %{
      "type" => "patch",
      "base_version" => 0,
      "version" => 1,
      "ops" => [...],
      "stream_ops" => [...]
    }

## Telemetry

  * `[:musubi, :channel, :join]` — `%{system_time: integer}`. Metadata:
    `module`, `id`, `topic`, `page_pid`.
  * `[:musubi, :channel, :terminate]` — `%{system_time: integer}`.
    Metadata: `module`, `id`, `topic`, `reason`, `page_pid`.

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*Consult [api-reference.md](api-reference.md) for complete listing*