fix: keep every word of an unquoted prompt, and stop a typo from starting a session

[hbrooks]

Summary

Two problems with the bare-prompt shorthand, found while asking how to prevent typos from starting sessions.

1. Unquoted prompts lost every word but the first. agent fix the tests started a session with the prompt "fix". The rest was dropped silently, no error. [prompt] was a single positional, and commander does not complain about excess args. session handoff <prompt> had the identical bug.

Now [prompt...], joined on spaces. This also gives -- a useful meaning for free, which was the sticking point on the original idea of requiring agent -- <prompt>:

agent fix the tests                    -> "fix the tests"
agent fix the tests --model claude-fable-5   -> prompt and flag split correctly
agent -- why does -m fail              -> "why does -m fail"
agent --model z -- why does -m fail    -> flag parsed, rest is prompt

2. A mistyped command started a session. agent sesion ran as a prompt. Now:

$ agent sesion
error: unknown command "sesion"
  did you mean "agent session"?
  to start a session with that prompt: agent -p sesion
  to see every command: agent --help

Exits 1. Nothing starts. With no near match (agent xyzzy) the suggestion line is omitted and the rest stays.

The guard keys on shape, not edit distance

One bare word with no whitespace and no leading dash is a typo. Anything longer is a prompt. Edit distance only picks the wording of the hint; it never decides whether to block.

That distinction matters. Gating on distance alone would have been much worse than the bug it fixes. Measured against 68 common prompt-opening words, 23 fall within commander's own match threshold of a command name:

typed	matches	would have been refused
revert	review	agent revert the migration
audit	budget	agent audit the deps
test	host	agent test the parser
log / logs	login	agent logs are missing
find	ping	agent find the leak

Also: update/usage, make/me, explain/template, look/hook, list/host, mock/hook, lint/ping, delete/template.

Known gap, left in deliberately

agent sesion list still starts a session. I prototyped the obvious fix, a near-miss first word plus a known subcommand, and it false-positived on revert list, audit list, test run, and port get. Refusing a real prompt is worse than missing a typo, so the single-token rule stands alone. Easy to revisit.

Notes

• Suggestions only name documented spellings. Hidden plural aliases still dispatch but never appear in a hint.
• Quoting a single word cannot get through, since the shell strips the quotes. That is why the error names -p and not quoting.
• The similarCommands helper is a local Damerau-Levenshtein. Commander has one internally but does not export it, and its top-level unknown-command error is unreachable here anyway, because the shorthand intercepts first.

Test plan

• vitest run green: 421 tests, 23 files. 13 new.
• tsc --noEmit clean.
• Prompt joining covered end to end, stubbing startAgentSession and parsing real argv: unquoted, quoted, trailing flags, promptless.
• Typo guard unit-tested: single word, multi-word prompt, leading dash, --, one word plus a flag.
• Driven against the real CLI: sesion, reveiw, instal, confg all blocked with exit 1; xyzzy blocked with no suggestion; session, sessions, --version, --help dispatch unchanged; -p refactor and -- refactor both get through.

Verified by unit test and by tsx src/cli.tsx rather than a live session, because the shorthand path hardcodes --connect and cannot run headless.

[ellipsis-dev]

Important

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