agent endpoints: address an unnamed deployment as "_" (#4997)

An unnamed deployment was addressed as "default" and that spelling leaked
into scope keys, so embedders keyed endpoints differently from job dispatch.
Map "_" back to "" at the URL boundary, as the agent name already does,
and drop NormalizeDeployment.

pkg/agent/endpoint/front.go

@@ -415,10 +415,13 @@ func splitEndpointPath(u *url.URL) (endpointPath, error) {
 		return endpointPath{}, errMalformedPath
 	}
 	// "_" and "%5F" both land here; neither is a registrable name
-	// (IsReservedAgentName)
-	if agentName == UnnamedAgentSegment {
+	// (IsReservedAgentName, ValidateDeployment)
+	if agentName == UnnamedSegment {
 		agentName = ""
 	}
+	if deployment == UnnamedSegment {
+		deployment = ""
+	}
 	return endpointPath{agentName: agentName, deployment: deployment, path: path, escPath: escPath}, nil
 }
 

pkg/agent/endpoint/front_test.go

@@ -287,6 +287,10 @@ func TestSplitEndpointPath(t *testing.T) {
 		{name: "bare underscore is unnamed", target: "/agents/_/d/x", agentName: "", deployment: "d", path: "/x", escPath: "/x"},
 		{name: "encoded underscore is unnamed", target: "/agents/%5F/d/x", agentName: "", deployment: "d", path: "/x", escPath: "/x"},
 		{name: "double encoded underscore is a name", target: "/agents/%255F/d/x", agentName: "%5F", deployment: "d", path: "/x", escPath: "/x"},
+		{name: "bare underscore deployment is unnamed", target: "/agents/a/_/x", agentName: "a", deployment: "", path: "/x", escPath: "/x"},
+		{name: "encoded underscore deployment is unnamed", target: "/agents/a/%5F/x", agentName: "a", deployment: "", path: "/x", escPath: "/x"},
+		{name: "unnamed agent and deployment", target: "/agents/_/_/x", agentName: "", deployment: "", path: "/x", escPath: "/x"},
+		{name: "default is a deployment name", target: "/agents/a/default/x", agentName: "a", deployment: "default", path: "/x", escPath: "/x"},
 
 		{name: "not an endpoint path", target: "/other/x", err: errNotEndpointPath},
 		{name: "no deployment segment", target: "/agents/a", err: errNotEndpointPath},

pkg/agent/endpoint/registry.go

@@ -21,29 +21,15 @@ import (
 	"sync/atomic"
 )
 
-// DefaultDeployment is the URL segment that addresses workers registered with an
-// empty deployment name (self-hosted workers typically set none).
-const DefaultDeployment = "default"
-
-// UnnamedAgentSegment is the URL segment that addresses workers registered with
-// an empty agent name.
-const UnnamedAgentSegment = "_"
+// UnnamedSegment is the URL segment that addresses workers registered with an
+// empty agent name or deployment.
+const UnnamedSegment = "_"
 
 // IsReservedAgentName reports whether a name cannot address a worker. These are
 // unreserved characters (RFC 3986 §2.3), so percent-encoding them yields no
 // distinct form to address them by.
 func IsReservedAgentName(agentName string) bool {
-	return agentName == UnnamedAgentSegment || agentName == "." || agentName == ".."
-}
-
-// NormalizeDeployment maps an empty deployment to the segment that addresses it
-// in a URL. Every embedder must key its scopes through this, or a worker that
-// registered without a deployment is unreachable from any node but its own.
-func NormalizeDeployment(d string) string {
-	if d == "" {
-		return DefaultDeployment
-	}
-	return d
+	return agentName == UnnamedSegment || agentName == "." || agentName == ".."
 }
 
 // DefaultMaxStreams is the soft per-session concurrency cap used only for

pkg/service/agentendpointscope.go

@@ -32,7 +32,7 @@ type endpointScopeKey struct {
 }
 
 func newEndpointScopeKey(apiKey, agentName, deployment string) endpointScopeKey {
-	return endpointScopeKey{apiKey, agentName, endpoint.NormalizeDeployment(deployment)}
+	return endpointScopeKey{apiKey, agentName, deployment}
 }
 
 // EndpointScopes maps that tenancy onto the endpoint package's scopes, one per