[codex] Honor explicit end-to-end Product Design requests

[fchen-oai]

Summary

• keep concept selection as the default Product Design behavior
• bypass selection only when the user's original request explicitly asks not to stop or asks for end-to-end completion
• align the router, prototype workflow, and ideation output with that narrow exception

Root cause

The prototype and ideation workflows required a user selection even when the original request explicitly asked for a complete end-to-end build. The repeated gates stopped delivery before either requested artifact was implemented.

Feedback report: https://app.notion.com/p/openai/2026-06-10-05-02-15-128069-PDT-37b8e50b62b081ec84ebf2550c4914f4

Validation

• verified selection still stops by default in the router, prototype workflow, and ideation workflow
• verified the exception requires explicit language in the original request
• verified the downstream route and output instructions preserve the same policy
• git diff --check