Rebrand user-visible CLI text; add legacy fallbacks for keyring, cache dir and version prefix

Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>

internal/clientcache/cmd/cache/start.go

@@ -24,7 +24,6 @@ import (
 )
 
 const (
-	dotDirname  = ".boundary"
 	pidFileName = "cache.pid"
 	logFileName = "cache.log"
 
@@ -54,16 +53,16 @@ type StartCommand struct {
 }
 
 func (c *StartCommand) Synopsis() string {
-	return "Start a Boundary cache"
+	return "Start a Threshold cache"
 }
 
 func (c *StartCommand) Help() string {
 	helpText := `
-Usage: boundary cache start [options]
+Usage: threshold cache start [options]
 
   Start a cache:
 
-      $ boundary cache start
+      $ threshold cache start
 
   For a full list of examples, please see the documentation.
 
@@ -78,7 +77,7 @@ func (c *StartCommand) Flags() *base.FlagSets {
 	f.StringVar(&base.StringVar{
 		Name:       "log-level",
 		Target:     &c.flagLogLevel,
-		EnvVar:     "BOUNDARY_LOG_LEVEL",
+		EnvVar:     "THRESHOLD_LOG_LEVEL",
 		Completion: complete.PredictSet("trace", "debug", "info", "warn", "err"),
 		Usage: "Log verbosity level, mostly as a fallback for events. Supported values (in order of more detail to less) are " +
 			"\"trace\", \"debug\", \"info\", \"warn\", and \"err\".",
@@ -255,7 +254,7 @@ func DefaultDotDirectory(ctx context.Context) (string, error) {
 	if err != nil {
 		return "", errors.Wrap(ctx, err, op)
 	}
-	return filepath.Join(homeDir, dotDirname), nil
+	return daemon.DotDirectory(homeDir), nil
 }
 
 // logFile returns a log file which is rotated after it reaches the provided