feat: check agent API version on connection (#11696)

fixes #10531

Adds a check for `version` on connection to the Agent API websocket endpoint.  This is primarily for future-proofing, so that up-level agents get a sensible error if they connect to a back-level Coderd.

It also refactors the location of the `CurrentVersion` variables, to be part of the `proto` packages, since the versions refer to the APIs defined therein.

enterprise/coderd/workspaceproxycoordinate.go

@@ -11,7 +11,7 @@ import (
 	"github.com/coder/coder/v2/coderd/util/apiversion"
 	"github.com/coder/coder/v2/codersdk"
 	"github.com/coder/coder/v2/enterprise/wsproxy/wsproxysdk"
-	agpl "github.com/coder/coder/v2/tailnet"
+	"github.com/coder/coder/v2/tailnet/proto"
 )
 
 // @Summary Agent is legacy
@@ -59,7 +59,7 @@ func (api *API) workspaceProxyCoordinate(rw http.ResponseWriter, r *http.Request
 	if qv != "" {
 		version = qv
 	}
-	if err := agpl.CurrentVersion.Validate(version); err != nil {
+	if err := proto.CurrentVersion.Validate(version); err != nil {
 		httpapi.Write(ctx, rw, http.StatusBadRequest, codersdk.Response{
 			Message: "Unknown or unsupported API version",
 			Validations: []codersdk.ValidationError{

enterprise/wsproxy/wsproxysdk/wsproxysdk.go

@@ -439,7 +439,7 @@ func (c *Client) DialCoordinator(ctx context.Context) (agpl.MultiAgentConn, erro
 		return nil, xerrors.Errorf("parse url: %w", err)
 	}
 	q := coordinateURL.Query()
-	q.Add("version", agpl.CurrentVersion.String())
+	q.Add("version", proto.CurrentVersion.String())
 	coordinateURL.RawQuery = q.Encode()
 	coordinateHeaders := make(http.Header)
 	tokenHeader := codersdk.SessionTokenHeader

enterprise/wsproxy/wsproxysdk/wsproxysdk_test.go

@@ -194,7 +194,7 @@ func TestDialCoordinator(t *testing.T) {
 				return
 			}
 			version := r.URL.Query().Get("version")
-			if !assert.Equal(t, version, agpl.CurrentVersion.String()) {
+			if !assert.Equal(t, version, proto.CurrentVersion.String()) {
 				return
 			}
 			nc := websocket.NetConn(r.Context(), conn, websocket.MessageBinary)