fix(codex): suppress structured skill handoff blocks in normal console output

[pitimon]

Context

The structured-output protocol currently asks producer skills such as /requirements, /design, /breakdown, and /review-ai to append blocks like:

[/requirements] COMPLETE SKILL_OUTPUT:requirements
<!-- SKILL_OUTPUT:requirements
...
END_SKILL_OUTPUT -->

This is reasonable for downstream skill handoff: cross-verify can parse the metadata.

Codex integration problem

When these skills are used through Codex, the console/transcript exposes the raw HTML comment and the visible attribution line to the end user. Markdown comments are not hidden in that surface, so every requirements/review interaction can emit a large YAML-like internal metadata block.

This is not sensitive data by itself, but it is noisy, confuses users, and weakens the intended concise output of the Significance profile.

Reproduction

1. Use /requirements through Codex on a multi-file change.
2. Observe the skill response in the Codex console/transcript.
3. The SKILL_OUTPUT:requirements attribution and HTML-comment payload are rendered as ordinary output instead of remaining invisible metadata.

Expected

• Normal Codex user-facing output should contain the concise human summary only.
• Structured handoff metadata should remain available to a real consumer such as /cross-verify, but should not be printed when no consumer needs it.

Suggested compatibility-safe options

1. Emit SKILL_OUTPUT only when a consumer is explicitly requested or artifacts are persisted.
2. Add a Codex-aware output mode that stores handoff metadata in a local artifact/session channel rather than response text.
3. At minimum, make the visible attribution line optional and document the renderer limitation.

Please preserve the existing Claude/Markdown workflow where HTML comments are actually hidden. This looks like a cross-runtime output-contract mismatch rather than a defect in the requirements content itself.

Evidence

• skills/requirements/SKILL.md requires the structured output block at the end of the result.
• guides/structured-output-protocol.md says the HTML comment is invisible when rendered.
• In Codex console it is visibly rendered verbatim.