measurements --types: invalid codes return Withings 503 'Invalid Params' instead of friendly error

[DTTerastar]

Severity

minor

Summary

measurements --types accepts any string and forwards it verbatim to the Withings API. Non-numeric input bubbles up as an unhelpful HTTP-503-shaped error; unknown numeric codes silently return an empty result.

Reproduce

$ withings-export measurements --types abc --since 7d
Error: withings API status 503: Invalid Params
Usage:
  withings-export measurements [flags]
  ...

$ withings-export measurements --types 999 --since 30d --json
null

Expected

• Validate --types is a comma-separated list of positive integers locally before calling the API; on bad input, error with invalid --types value "abc": expected comma-separated integers (e.g. 1,6,76).
• For unknown but well-formed codes, follow the contract: empty [], exit 0. (Right now the empty case is null — duplicate of Empty JSON output is 'null' instead of '[]' — breaks jq pipelines #16, but worth confirming the same fix covers it.)
• The Withings 503 wrap is also misleading — Withings returns HTTP 200 with a non-zero status code in the body; the CLI is rendering that body status as if it were an HTTP status. Render as e.g. withings API error 503: Invalid Params without status.

[DTTerastar]

Confirmed still reproduces against HEAD b580683. measurements --types abc --since 7d -> Error: withings API status 503: Invalid Params plus full usage dump and EXIT=1. measurements --types 999 --since 30d --format json -> [] with EXIT=0 (the empty-result case is now correct per #16, so the second half of this issue is no longer separate — only local validation + the misleading 503 wrap remain).

[Terastar-Paperclip]

Thanks — three distinct sub-issues teased apart cleanly.

Triage: kind:bug · area:format · priority:medium per TRIAGE.md.

Status notes:

• The empty-result-as-null part is the same surface as Empty JSON output is 'null' instead of '[]' — breaks jq pipelines #16, which is already closed — worth confirming the new behaviour covers --types 999 as part of this fix.
• Pre-flight validation of --types as a comma-separated integer list is a small targeted fix; on bad input, CONTRACT §3 (stderr-only, non-zero exit) is the right shape.
• The "503 Invalid Params" wrapping the Withings body status is a separate error-rendering bug worth pinning down regardless of the validator fix.

Routing: Lead Go Engineer.