feat(agent): populate subagent ID for terraform-defined devcontainers (#21942)

Completes the final piece of the puzzle. Support the pre-creation flow
from the agent side.

codersdk/agentsdk/convert.go

@@ -425,11 +425,20 @@ func DevcontainerFromProto(pdc *proto.WorkspaceAgentDevcontainer) (codersdk.Work
 	if err != nil {
 		return codersdk.WorkspaceAgentDevcontainer{}, xerrors.Errorf("parse id: %w", err)
 	}
+	var subagentID uuid.NullUUID
+	if pdc.SubagentId != nil {
+		subagentID.Valid = true
+		subagentID.UUID, err = uuid.FromBytes(pdc.SubagentId)
+		if err != nil {
+			return codersdk.WorkspaceAgentDevcontainer{}, xerrors.Errorf("parse subagent id: %w", err)
+		}
+	}
 	return codersdk.WorkspaceAgentDevcontainer{
 		ID:              id,
 		Name:            pdc.Name,
 		WorkspaceFolder: pdc.WorkspaceFolder,
 		ConfigPath:      pdc.ConfigPath,
+		SubagentID:      subagentID,
 	}, nil
 }
 
@@ -442,10 +451,16 @@ func ProtoFromDevcontainers(dcs []codersdk.WorkspaceAgentDevcontainer) []*proto.
 }
 
 func ProtoFromDevcontainer(dc codersdk.WorkspaceAgentDevcontainer) *proto.WorkspaceAgentDevcontainer {
+	var subagentID []byte
+	if dc.SubagentID.Valid {
+		subagentID = dc.SubagentID.UUID[:]
+	}
+
 	return &proto.WorkspaceAgentDevcontainer{
 		Id:              dc.ID[:],
 		Name:            dc.Name,
 		WorkspaceFolder: dc.WorkspaceFolder,
 		ConfigPath:      dc.ConfigPath,
+		SubagentId:      subagentID,
 	}
 }

codersdk/agentsdk/convert_test.go

@@ -136,6 +136,7 @@ func TestManifest(t *testing.T) {
 				ID:              uuid.New(),
 				WorkspaceFolder: "/home/coder/coder",
 				ConfigPath:      "/home/coder/coder/.devcontainer/devcontainer.json",
+				SubagentID:      uuid.NullUUID{Valid: true, UUID: uuid.New()},
 			},
 		},
 	}