Wire impl classes to interfaces (inherit; relocate SendHandler)

- Waku : IKernel, MessagingClient : IMessagingClient,
  ReliableChannelManager : IReliableChannelManager.
- The operation procs already live in PR#3989's decomposed */api/ modules and
  stay as plain procs (nothing dispatches through the interface types, so no
  method-ization is needed).
- SendHandler now lives in reliable_channel_manager_api.nim (its PR#3975 home);
  removed the duplicate from reliable_channel.nim, which re-exports the
  interface module so channels/api/{channel_lifecycle,send} still see it.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

logos_delivery/channels/reliable_channel.nim

@@ -22,6 +22,7 @@ import stew/byteutils
 import libp2p/crypto/crypto as libp2p_crypto
 
 import logos_delivery/api/types
+import logos_delivery/api/reliable_channel_manager_api
 import logos_delivery/messaging/delivery_service/send_service
 import logos_delivery/waku/waku_core/topics
 
@@ -32,8 +33,8 @@ import ./rate_limit_manager/rate_limit_manager
 import ./encryption/encryption
 
 export
-  types, send_service, events, segmentation, scalable_data_sync, rate_limit_manager,
-  encryption
+  types, reliable_channel_manager_api, send_service, events, segmentation,
+  scalable_data_sync, rate_limit_manager, encryption
 
 const LipWireReliableChannelVersion* = "RELIABLE-CHANNEL-API/1"
   ## Wire-format spec marker for the Reliable Channel layer, as defined
@@ -44,14 +45,6 @@ const LipWireReliableChannelVersion* = "RELIABLE-CHANNEL-API/1"
   ## on breaking on-the-wire changes; implementations pin one version.
 
 type
-  SendHandler* = proc(envelope: MessageEnvelope): Future[Result[RequestId, string]] {.
-    async: (raises: [CatchableError]), gcsafe
-  .}
-    ## Egress dispatch boundary. Typically wraps `MessagingClient.send`;
-    ## tests inject a fake that records calls and returns canned
-    ## `RequestId`s so the send state machine can be exercised end-to-end
-    ## without a network.
-
   MessagePersistence {.pure.} = enum
     Persistent
     Ephemeral

logos_delivery/channels/reliable_channel_manager.nim

@@ -16,6 +16,7 @@ import brokers/broker_context
 import logos_delivery/messaging/messaging_client
 import logos_delivery/messaging/api/send
 import logos_delivery/api/types
+import logos_delivery/api/reliable_channel_manager_api
 
 import ./reliable_channel
 
@@ -27,7 +28,7 @@ type
     ## channel API. Placeholder for now (segmentation / SDS / rate-limit defaults
     ## will move here in a follow-up PR); kept so each layer owns its own config.
 
-  ReliableChannelManager* = ref object
+  ReliableChannelManager* = ref object of IReliableChannelManager
     channels*: Table[ChannelId, ReliableChannel] ## read by `channels/api.nim`
     messagingClient: MessagingClient ## The channel layer chains onto messaging.
     sendHandler*: SendHandler

logos_delivery/messaging/messaging_client.nim

@@ -3,6 +3,7 @@
 ## `messaging/api.nim`.
 import results, chronos
 import
+  logos_delivery/api/messaging_client_api,
   logos_delivery/waku/node/waku_node,
   logos_delivery/messaging/delivery_service/[recv_service, send_service]
 
@@ -13,7 +14,7 @@ type
     ## follow-up PR. Today it only carries the p2p reliability toggle.
     useP2PReliability*: bool
 
-  MessagingClient* = ref object
+  MessagingClient* = ref object of IMessagingClient
     node*: WakuNode ## Waku core driven by this layer; read by `messaging/api.nim`.
     sendService*: SendService
     recvService*: RecvService

logos_delivery/waku/waku.nim

@@ -22,6 +22,7 @@ import
   metrics/chronos_httpserver,
   brokers/broker_context,
   logos_delivery/api/types,
+  logos_delivery/api/kernel_api,
   logos_delivery/waku/[
     waku_core,
     waku_node,
@@ -63,7 +64,7 @@ logScope:
 # Git version in git describe format (defined at compile time)
 const git_version* {.strdefine.} = "n/a"
 
-type Waku* = ref object
+type Waku* = ref object of IKernel
   stateInfo*: WakuStateInfo
   conf*: WakuConf
   rng*: crypto.Rng