fix(cli): keep --json stdout payload-only by routing logger status to stderr

[John-David Dalton (jdalton)]

socket <cmd> --json leaked non-JSON onto stdout, breaking | jq and scripted use. Closes the ASK-115 loop: --json implies a clean stdout, no new --no-log flag.

Root cause

The lib logger routes its step / substep status helpers to stdout, while every other status helper (info / warn / success / fail) and the whole spinner go to stderr. Progress lines emitted via substep (e.g. the fix PR-cleanup step, the SDK unreadable-file notice) therefore landed on the payload stream under --json.

Fix

At the argv-parse boundary — not per command — when machine-output mode (--json / --markdown / --quiet) is engaged, step / substep are routed to stderr to match the spinner. logger.log is left untouched: it's the payload / primary-data channel (JSON, Markdown, and output-kind-gated human text all flow through it), so it stays on stdout.

New module util/output/machine-output-streams.mts, wired into both meowOrExit and meowWithSubcommands right after setMachineOutputMode.

Receipts

• socket whoami --json → stdout is JSON only, stderr empty (payload path unchanged).
• New unit test: step / substep route to stderr under --json / --markdown / --quiet, stay on stdout with no machine flag, and restore afterward.

test + check output

✓ test/unit/util/output/machine-output-streams.test.mts (5 tests)
✓ test/unit/util/output/ (all suites, 199 tests incl. ambient-mode, emit-payload, mode)
✓ test/unit/util/cli/ (with-subcommands, 56 tests)
✓ cmd-organization-quota (12) + cmd-scan-view (19)
[check] 132 check(s) passed

Scope

Commands with incomplete --json support (some manifest generators emit unguarded logger.log chatter, acknowledged in-code) are out of scope — this fixes the structural status-helper leak that affects every properly---json-capable command.

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Note

Low Risk
Localized CLI output routing at parse time with restore semantics; no auth, data, or API behavior changes.

Overview
Fixes socket <cmd> --json (and --markdown / --quiet) leaking progress text onto stdout when commands use the shared logger’s step / substep helpers, which otherwise write to stdout unlike other status helpers.

Adds applyMachineOutputStreamPolicy in machine-output-streams.mts: at argv-parse time it temporarily shadows step / substep onto logger.error (stderr) while machine-output mode is active, restores defaults when it is not, and leaves logger.log on stdout for payloads. Wired immediately after setMachineOutputMode in meowOrExit and meowWithSubcommands, with unit tests for engage/restore behavior across machine flags.

^{Reviewed by Cursor Bugbot for commit ed010bf. Configure here.}