Cache runtime version metadata fallback

internal/runtimeinfo/version.go

@@ -2,14 +2,26 @@
 // public buildinfo facade.
 package runtimeinfo
 
-import "runtime/debug"
+import (
+	"runtime/debug"
+	"sync"
+)
 
 var injectedVersion string
 
 // Version returns the injected version or the running executable's main module
 // version, falling back to "dev" when neither provides a release identifier.
 func Version() string {
-	return version(injectedVersion, debug.ReadBuildInfo)
+	if injectedVersion != "" {
+		return injectedVersion
+	}
+	return fallbackVersion()
+}
+
+var fallbackVersion = newFallbackVersion(debug.ReadBuildInfo)
+
+func newFallbackVersion(readBuildInfo func() (*debug.BuildInfo, bool)) func() string {
+	return sync.OnceValue(func() string { return version("", readBuildInfo) })
 }
 
 func version(injected string, readBuildInfo func() (*debug.BuildInfo, bool)) string {