docs(roadmap): add #351 — cost command returns no dollar amount; identical to stats

ROADMAP.md

@@ -6281,3 +6281,5 @@ Original filing (2026-04-18): the session emitted `SessionStart hook (completed)
 340. **Resume-safe `/session help --output-format json` writes its primary JSON error envelope to stderr and uses `type` instead of the session JSON `kind` vocabulary** — dogfooded 2026-04-29 on current `origin/main` / rebuilt `./rust/target/debug/claw` with embedded `git_sha` `dc47482e`. Running `./rust/target/debug/claw --resume latest /session help --output-format json` wrote no stdout bytes, but wrote a JSON error object to stderr: `{"command":"/session help","error":"Unknown /session action ...","type":"error"}`. Meanwhile `/session list --output-format json` wrote valid stdout JSON with `kind=session_list`. The JSON output contract is therefore split across stderr for an error/help-ish action and switches vocabulary from `kind` to `type`; automation that reads stdout sees empty/non-JSON output and cannot handle errors consistently with successful session JSON responses. **Required fix shape:** (a) all `--output-format json` command responses, including resumed slash errors, should emit the primary JSON envelope on stdout; (b) use `kind:"error"` or a documented error schema consistently instead of an ad hoc `type` field; (c) reserve stderr prose for text mode or optional non-primary diagnostics, not the machine-readable envelope; (d) add a regression for `/session help` or an unsupported `/session` action under `--resume` proving stdout contains the structured JSON error envelope and stderr does not carry the only parseable payload. **Why this matters:** claws need one stdout JSON contract for both success and failure. If a help-ish session error is silently moved to stderr and shaped differently from `session_list`, orchestration lanes cannot distinguish an unsupported action from transport corruption or an empty response without bespoke stderr parsing. Source: gaebal-gajae dogfood follow-up for the 15:30 nudge on rebuilt `./rust/target/debug/claw` `dc47482e`.
 
 341. **Resume-safe `/tasks --output-format json` emits an unsupported-command JSON error only on stderr and mixes `kind` with `type` classification vocabularies** — dogfooded 2026-04-29 for the 16:00 nudge on current `origin/main` / rebuilt `./rust/target/debug/claw` with embedded `git_sha` `58569131`. Running `./rust/target/debug/claw --resume latest /tasks --output-format json` wrote no stdout bytes, but wrote a JSON error object to stderr: `{"command":"/tasks","error":"/tasks is not yet implemented in this build","kind":"unsupported_command","type":"error"}`. The unsupported command envelope therefore has two separate top-level classification vocabularies (`kind=unsupported_command` and `type=error`) and places the only parseable payload on stderr, while successful JSON commands use stdout and a `kind`-only classification. This is distinct from #340 because it is not session help; it shows implemented-but-unsupported command stubs can emit a dual-vocabulary error envelope. **Required fix shape:** (a) in `--output-format json` mode, emit the primary JSON envelope on stdout for unsupported resumed slash commands such as `/tasks`; (b) document and use one error discriminator, preferably `kind:"error"` plus `code:"unsupported_command"`, or `kind:"unsupported_command"` plus `status:"error"`, but not `type`; (c) reserve stderr for non-primary diagnostics or text-mode prose, never as the sole JSON payload; (d) add regression coverage for `/tasks` under `--resume` with JSON output proving stdout contains the structured error envelope, stderr is not the only parseable stream, and the envelope uses the documented single-vocabulary discriminator. **Why this matters:** claws need the same stdout JSON contract for implemented successes and implemented-but-unsupported stubs. If `/tasks` errors can silently move to stderr and advertise both `kind` and `type`, automation must special-case command stubs instead of applying one JSON error parser. Source: gaebal-gajae dogfood follow-up for the 16:00 nudge on rebuilt `./rust/target/debug/claw` `58569131`.
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+351. **`/cost --output-format json` returns only token counts, not a dollar-amount cost figure; `/cost` and `/stats` produce identical JSON payloads differing only in `"kind"`** — dogfooded 2026-04-30 by Jobdori on `f65b2b4`. Running `claw --output-format json --resume latest /cost` returns `{"kind":"cost","cache_creation_input_tokens":0,"cache_read_input_tokens":0,"input_tokens":0,"output_tokens":0,"total_tokens":0}`. There is no `total`, `cost_usd`, `cost`, or `currency` field. The command is named `/cost` which implies a monetary figure; an orchestration lane budgeting API spend cannot use this command to check whether a spending threshold has been reached. Additionally, `diff`ing `/cost` vs `/stats` output (minus `kind`) returns no differences — the two commands are functionally identical, which means either `/cost` should add monetary fields to justify its existence, or the two commands should be merged with a single canonical name. **Required fix shape:** (a) add `cost_usd` (or `cost` + `currency`) to `/cost --output-format json` output so callers can programmatically check spend; (b) if token→cost conversion requires a model-specific rate table, expose the rate used (e.g. `"rate": {"input_per_mtok": 3.0, "output_per_mtok": 15.0}`) so callers can verify or override the calculation; (c) if `/stats` is intentionally distinct, document how it differs from `/cost` in `/help --output-format json`; if they are truly equivalent, deprecate one and point to the other; (d) regression coverage proving `/cost --output-format json` includes at minimum a `cost_usd` or equivalent field. Source: Jobdori live dogfood, mengmotaHost, `f65b2b4`, 2026-04-30.