Improve tsh debug messages with client version output

tool/tsh/common/tsh.go

@@ -1632,6 +1632,18 @@ func Run(ctx context.Context, args []string, opts ...CliOption) error {
 		defer runtimetrace.Stop()
 	}
 
+	// print tsh version when --debug flag is set
+	// to diagnose potential client version mismatch
+	if cf.Debug && command != ver.FullCommand() {
+		logger.InfoContext(ctx, "Initializing tsh",
+			"version", slog.GroupValue(
+				slog.String("teleport", teleport.Version),
+				slog.String("teleport_git", teleport.Gitref),
+				slog.String("go", runtime.Version()),
+			),
+		)
+	}
+
 	switch command {
 	case ver.FullCommand():
 		err = onVersion(&cf)

tool/tsh/common/tsh_test.go

@@ -7749,3 +7749,23 @@ func Test_humanFriendlyValidUntilDuration(t *testing.T) {
 		})
 	}
 }
+
+func TestDebugVersionOutput(t *testing.T) {
+	t.Setenv(tshBinMainTestEnv, "1")
+	testExecutable, err := os.Executable()
+	require.NoError(t, err)
+
+	output, err := exec.Command(testExecutable, "logout", "--debug").CombinedOutput()
+	require.NoError(t, err)
+
+	vers := []string{
+		teleport.Version,
+		teleport.Gitref,
+		runtime.Version(),
+	}
+
+	require.Contains(t, string(output), "Initializing tsh version")
+	for _, v := range vers {
+		require.Contains(t, string(output), v)
+	}
+}