## Problem
Users commonly type `claw doctor --json`, `claw status --json`, or
`claw system-prompt --json` expecting JSON output. These fail with
`unrecognized argument \`--json\` for subcommand` with no hint that
`--output-format json` is the correct flag.
## Discovery
Filed as #152 during 21:17 dogfood nudge. The #127 worktree contained
a more comprehensive patch but conflicted with #141 (unified --help).
On re-investigation of main, Bugs 1 and 3 from #127 are already closed
(positional arg rejection works, no double "error:" prefix). Only
Bug 2 (the `--json` hint) remained.
## Fix
Two call sites add the hint:
1. `parse_single_word_command_alias`'s diagnostic-verb suffix path:
when rest[1] == "--json", append "Did you mean \`--output-format json\`?"
2. `parse_system_prompt_options` unknown-option path: same hint when
the option is exactly `--json`.
## Verification
Before:
$ claw doctor --json
error: unrecognized argument `--json` for subcommand `doctor`
Run `claw --help` for usage.
After:
$ claw doctor --json
error: unrecognized argument `--json` for subcommand `doctor`
Did you mean `--output-format json`?
Run `claw --help` for usage.
Covers: `doctor --json`, `status --json`, `sandbox --json`,
`system-prompt --json`, and any other diagnostic verb that routes
through `parse_single_word_command_alias`.
Other unrecognized args (`claw doctor garbage`) correctly don't
trigger the hint.
## Tests
- 2 new assertions in `parses_multiple_diagnostic_subcommands`:
- `claw doctor --json` produces hint
- `claw doctor garbage` does NOT produce hint
- 177 rusty-claude-cli tests pass
- Workspace tests green
Closes ROADMAP #152.
79352a2d20