A missing mandatory option crashes with a stack trace instead of printing the usage

[riker-wamf]

Description

A command that declares an option mandatory: true does not report a missing option cleanly. It crashes with an unhandled Dart exception and a stack trace.

mandatory: true does not fail when the arguments are parsed. package:args throws an ArgumentError from ArgResults.[], which is the moment the command reads the option inside runAuthenticated. DartSlackCommandRunner.run catches FormatException and UsageException only, so the ArgumentError escapes to main.

Steps to reproduce

Measured on main at commit dfadc64:

$ dart run bin/dart_slack.dart history
Unhandled exception:
Invalid argument(s): Option channel is mandatory.
#0      ArgResults.[] (package:args/src/arg_results.dart:74:7)
#1      HistoryCommand.runAuthenticated (package:dart_slack/src/cli/commands/history_command.dart:38:32)
#2      AuthenticatedCommand.run (package:dart_slack/src/cli/commands/authenticated_command.dart:74:20)
#3      CommandRunner.runCommand (package:args/command_runner.dart:212:27)
#4      CompletionCommandRunner.runCommand (package:cli_completion/src/command_runner/completion_command_runner.dart:89:18)
#5      DartSlackCommandRunner.runCommand (package:dart_slack/src/cli/command_runner.dart:130:30)
#6      DartSlackCommandRunner.run (package:dart_slack/src/cli/command_runner.dart:74:20)
#7      main (file:///…/bin/dart_slack.dart:6:55)

Expected

The usage text, and exit code 64 (ExitCode.usage), the same as an invalid --limit value.

Affected commands

Every command that uses mandatory: true. grep -rn "mandatory: true" lib/ lists them.

Notes

• The credentials are loaded before the option is read, so a user with no token sees Not logged in instead. The crash needs a valid token or SLACK_TOKEN.
• The new search command in feat: add full-text search command (search.messages) #37 avoids this. It reads --query as a nullable value and prints the usage with exit 64. See PR feat: add full-text message search (search.messages) #43.

Possible fixes

1. Read each required option as nullable and validate it in the command, as search does. Explicit, and it gives each command a specific message.
2. Catch ArgumentError in DartSlackCommandRunner.run and convert it to a usage error. One change covers every command, but the message stays generic.