diff --git a/internal/api/agent_version_shared_test.go b/internal/api/agent_version_shared_test.go
new file mode 100644
index 0000000000..9c0d6efa7b
--- /dev/null
+++ b/internal/api/agent_version_shared_test.go
@@ -0,0 +1,56 @@
+package api
+
+import (
+	"encoding/json"
+	"net/http"
+	"net/http/httptest"
+	"os"
+	"testing"
+
+	"github.com/rcourtman/pulse-go-rewrite/internal/updates"
+)
+
+func TestHandleAgentVersionMatchesReleaseExecutableIdentity(t *testing.T) {
+	original := updates.BuildVersion
+	t.Cleanup(func() { updates.BuildVersion = original })
+	for _, tc := range []struct {
+		name, build, target, wire string
+		sourceMarker              bool
+	}{
+		{name: "stable", build: "6.6.0", target: "6.6.0", wire: "v6.6.0"},
+		{name: "prefixed stable", build: "v6.6.0", target: "6.6.0", wire: "v6.6.0"},
+		{name: "beta", build: "6.7.0-beta.1", target: "6.7.0-beta.1", wire: "v6.7.0-beta.1"},
+		{name: "candidate", build: "v6.6.0-rc.6", target: "6.6.0-rc.6", wire: "v6.6.0-rc.6"},
+		{name: "diagnostic", build: "6.6.0+git.1", wire: "dev"},
+		{name: "source build", build: "6.6.0", wire: "dev", sourceMarker: true},
+	} {
+		t.Run(tc.name, func(t *testing.T) {
+			t.Chdir(t.TempDir())
+			updates.BuildVersion = tc.build
+			if tc.sourceMarker {
+				if err := os.WriteFile("BUILD_FROM_SOURCE", []byte("1"), 0o644); err != nil {
+					t.Fatal(err)
+				}
+			}
+			// Fleet/display callers keep their existing canonical representation.
+			if got := currentAgentTargetVersion(); got != tc.target {
+				t.Fatalf("display target = %q, want %q", got, tc.target)
+			}
+			rr := httptest.NewRecorder()
+			(&Router{}).handleAgentVersion(rr, httptest.NewRequest(http.MethodGet, "/api/agent/version", nil))
+			var payload AgentVersionResponse
+			if err := json.Unmarshal(rr.Body.Bytes(), &payload); err != nil {
+				t.Fatal(err)
+			}
+			if rr.Code != http.StatusOK || payload.Version != tc.wire {
+				t.Fatalf("machine version = %q (HTTP %d), want %q", payload.Version, rr.Code, tc.wire)
+			}
+			if tc.target != "" && payload.Version != expectedAgentBinaryVersion(tc.target) {
+				t.Fatal("helper request and download validator disagree on executable identity")
+			}
+			if got := rr.Header().Get("Cache-Control"); got != "no-store, no-cache, must-revalidate, max-age=0" {
+				t.Fatalf("cache protection = %q", got)
+			}
+		})
+	}
+}
diff --git a/internal/api/router.go b/internal/api/router.go
index 80821941c7..6087f062ef 100644
--- a/internal/api/router.go
+++ b/internal/api/router.go
@@ -5886,7 +5886,11 @@ func (r *Router) handleAgentVersion(w http.ResponseWriter, req *http.Request) {
 		return
 	}
 
-	version := currentAgentTargetVersion()
+	// Installed helpers compare this wire value with the signed executable's
+	// --version output exactly. Use the same identity as the download validator
+	// and make build-agents (including its v prefix), not the server display
+	// version. Fixing only a new helper cannot unblock an old helper's update.
+	version := expectedAgentBinaryVersion(currentAgentTargetVersion())
 	if version == "" {
 		version = "dev"
 	}