## Problem
The `"prompt"` subcommand arm enforced `if prompt.trim().is_empty()`
and returned a specific error. The fallthrough `other` arm in the same
match block — which routes any unrecognized first positional arg to
`CliAction::Prompt` — had no such guard. Result:
$ claw ""
error: missing Anthropic credentials; export ANTHROPIC_AUTH_TOKEN ...
$ claw " "
error: missing Anthropic credentials; ...
$ claw "" ""
error: missing Anthropic credentials; ...
$ claw --output-format json ""
{"error":"missing Anthropic credentials; ...","type":"error"}
An empty prompt should never reach the credentials check. Worse: with
valid credentials, the literal empty string gets sent to Claude as a
user prompt, either burning tokens for nothing or triggering a model-
side refusal. Same prompt-misdelivery family as #145.
## Root cause
In `parse_subcommand()`, the final `other =>` arm in the top-level
match only guards against typos (#108 guard via `looks_like_subcommand_typo`)
and then unconditionally builds `CliAction::Prompt { prompt: rest.join(" ") }`.
An empty/whitespace-only join passes through.
## Changes
### rust/crates/rusty-claude-cli/src/main.rs
Added the same `if joined.trim().is_empty()` guard already used in the
`"prompt"` arm to the fallthrough path. Error message distinguishes it
from the `prompt` subcommand path:
empty prompt: provide a subcommand (run `claw --help`) or a
non-empty prompt string
Runs AFTER the typo guard (so `claw sttaus` still suggests `status`)
and BEFORE CliAction::Prompt construction (so no network call ever
happens for empty inputs).
### Regression tests
Added 4 assertions in the existing parse_args test:
- parse_args([""]) → Err("empty prompt: ...")
- parse_args([" "]) → Err("empty prompt: ...")
- parse_args(["", ""]) → Err("empty prompt: ...")
- parse_args(["sttaus"]) → Err("unknown subcommand: ...") [verifies #108 typo guard still takes precedence]
### ROADMAP.md
Added Pinpoint #147 documenting the gap, verification, root cause,
fix shape, and acceptance. Joins the prompt-misdelivery cluster
alongside #145.
## Live verification
$ claw ""
error: empty prompt: provide a subcommand (run `claw --help`) or a non-empty prompt string
$ claw " "
error: empty prompt: provide a subcommand (run `claw --help`) or a non-empty prompt string
$ claw --output-format json ""
{"error":"empty prompt: provide a subcommand ...","type":"error"}
$ claw prompt "" # unchanged: subcommand-specific error preserved
error: prompt subcommand requires a prompt string
$ claw hello # unchanged: typo guard still fires
error: unknown subcommand: hello.
Did you mean help
$ claw "real prompt here" # unchanged: real prompts still reach API
error: api returned 401 Unauthorized (with dummy key, as expected)
All empty/whitespace-only paths exit 1. No network call. No misleading
credentials error.
## Tests
- rusty-claude-cli bin: 177 tests pass (4 new assertions)
- Full workspace green except pre-existing resume_latest flake (unrelated)
Closes ROADMAP #147.
4cb8fa059a