Compact error output, fix four-dash bug, improve error messages (#1550)

* Initial plan

* Compact error output, fix four-dash bug, and improve error messages

- Suppress help text on parse errors using ParseErrorAction.ShowHelp = false
- Fix four-dash bug in JwtCommand.cs: jwtSigningKeyOption.Name already includes '--'
- Improve error messages across all validators for consistency:
  - Wrap invalid values in quotes for clarity
  - Add actionable hints (examples, allowed values)
  - Use consistent formatting pattern

Co-authored-by: waldekmastykarz <11164679+waldekmastykarz@users.noreply.github.com>

---------

Co-authored-by: copilot-swe-agent[bot] <198982749+Copilot@users.noreply.github.com>
Co-authored-by: waldekmastykarz <11164679+waldekmastykarz@users.noreply.github.com>
Co-authored-by: Waldek Mastykarz <waldek@mastykarz.nl>
Co-authored-by: Garry Trinder <garry@trinder365.co.uk>

Author: 3 people

DevProxy/Commands/DevProxyCommand.cs

@@ -3,6 +3,7 @@
 using DevProxy.Abstractions.Utils;
 using System.CommandLine;
 using System.CommandLine.Help;
+using System.CommandLine.Invocation;
 using System.CommandLine.Parsing;
 using System.Globalization;
 
@@ -218,6 +219,12 @@ public async Task<int> InvokeAsync(string[] args, WebApplication app)
         var parseResult = IsStdioCommand
             ? StdioCommand.ParseStdioArgs(this, args)
             : Parse(args);
+
+        if (parseResult.Action is ParseErrorAction parseErrorAction)
+        {
+            parseErrorAction.ShowHelp = false;
+        }
+
         var exitCode = await parseResult.InvokeAsync(app.Lifetime.ApplicationStopping);
 
         // Return exit code 2 for input validation and parse errors to distinguish
@@ -300,7 +307,7 @@ private void ConfigureCommand()
 
             if (!File.Exists(filePath))
             {
-                input.AddError($"Configuration file {filePath} does not exist");
+                input.AddError($"Configuration file '{filePath}' does not exist. Check the file path and try again.");
             }
         });
 
@@ -313,7 +320,7 @@ private void ConfigureCommand()
         {
             if (!System.Net.IPAddress.TryParse(input.Tokens[0].Value, out _))
             {
-                input.AddError($"{input.Tokens[0].Value} is not a valid IP address");
+                input.AddError($"'{input.Tokens[0].Value}' is not a valid IP address. Example: 127.0.0.1");
             }
         });
 
@@ -335,7 +342,7 @@ private void ConfigureCommand()
         {
             if (!Enum.TryParse<LogLevel>(input.Tokens[0].Value, true, out _))
             {
-                input.AddError($"{input.Tokens[0].Value} is not a valid log level. Allowed values are: {string.Join(", ", Enum.GetNames<LogLevel>())}");
+                input.AddError($"'{input.Tokens[0].Value}' is not a valid log level. Allowed values: {string.Join(", ", Enum.GetNames<LogLevel>())}");
             }
         });
 
@@ -417,7 +424,7 @@ private void ConfigureCommand()
             {
                 if (!long.TryParse(input.Tokens[0].Value, out var timeoutInput) || timeoutInput < 1)
                 {
-                    input.AddError($"{input.Tokens[0].Value} is not valid as a timeout value");
+                    input.AddError($"'{input.Tokens[0].Value}' is not a valid timeout value. Specify a positive integer (in seconds).");
                 }
             }
             catch (InvalidOperationException ex)
@@ -474,7 +481,7 @@ private void ConfigureCommand()
             }
             if (!Enum.TryParse<OutputFormat>(input.Tokens[0].Value, true, out _))
             {
-                input.AddError($"{input.Tokens[0].Value} is not a valid output format. Allowed values are: {string.Join(", ", Enum.GetNames<OutputFormat>())}");
+                input.AddError($"'{input.Tokens[0].Value}' is not a valid output format. Allowed values: {string.Join(", ", Enum.GetNames<OutputFormat>())}");
             }
         });
 

DevProxy/Commands/JwtCommand.cs

@@ -94,7 +94,7 @@ private void ConfigureCommand()
                 var value = input.GetValue(jwtSigningKeyOption);
                 if (string.IsNullOrWhiteSpace(value) || value.Length < 32)
                 {
-                    input.AddError($"Requires option '--{jwtSigningKeyOption.Name}' to be at least 32 characters");
+                    input.AddError($"Requires option '{jwtSigningKeyOption.Name}' to be at least 32 characters");
                 }
             }
             catch (InvalidOperationException ex)