Closes#21794.
`/kanban`, `/kanban help`, `/kanban --help`, and `/kanban <sub> -h`
all returned broken output to the gateway and interactive CLI. Three
underlying bugs in `hermes_cli.kanban.run_slash`:
1. argparse writes help to **stdout** but `run_slash` only captured
stderr at parse time, so `-h` text was silently swallowed and
replaced with the `(usage error: 0)` sentinel.
2. The wrapping parser used `prog="/"` and routed via a synthetic
"_top → kanban" subparser, producing `usage: / kanban …` (stray
space) and `usage: /kanban kanban …` (doubled token) in error text.
3. Bare `/kanban` and `/kanban help` dumped argparse's full ~3KB
usage tree, which reads as visual garbage in a chat bubble.
Fix: drive the kanban_parser directly (no double-wrap), rewrite prog
strings on every leaf subparser, capture stdout AND stderr around
parse_args, distinguish SystemExit(0) (help — return captured stdout)
from SystemExit(2) (error — return single-line ⚠-prefixed message),
and add an explicit chat-friendly short-help block returned for bare
invocation and the help aliases (`help`, `--help`, `-h`, `?`).
Added 5 regression tests covering bare invocation, every help alias,
subcommand help, unknown action, and missing required arg.
Affects every chat platform via gateway/run.py::_handle_kanban_command
and the interactive CLI via cli.py::_handle_kanban_command.
Co-Authored-By: Nagatha (Claude Opus 4.7) <noreply@anthropic.com>
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