chore: expose UpdateAppStatus on agentsocket (#22353)

relates to #21335

Adds UpdateAppStatus on the agentsocket, wired up to forward to Coderd over the dRPC connection the agent maintains.

Disclosure: I used AI to generate significant portions of this PR, but hand-reviewed and tweaked the code. I consider it approximately indistinguishable from what I would have done by hand.

agent/agentsocket/server.go

@@ -12,6 +12,7 @@ import (
 
 	"cdr.dev/slog/v3"
 	"github.com/coder/coder/v2/agent/agentsocket/proto"
+	agentproto "github.com/coder/coder/v2/agent/proto"
 	"github.com/coder/coder/v2/agent/unit"
 	"github.com/coder/coder/v2/codersdk/drpcsdk"
 )
@@ -120,6 +121,17 @@ func (s *Server) Close() error {
 	return nil
 }
 
+// SetAgentAPI sets the agent API client used to forward requests
+// to coderd.
+func (s *Server) SetAgentAPI(api agentproto.DRPCAgentClient28) {
+	s.service.SetAgentAPI(api)
+}
+
+// ClearAgentAPI clears the agent API client.
+func (s *Server) ClearAgentAPI() {
+	s.service.ClearAgentAPI()
+}
+
 func (s *Server) acceptConnections() {
 	// In an edge case, Close() might race with acceptConnections() and set s.listener to nil.
 	// Therefore, we grab a copy of the listener under a lock. We might still get a nil listener,