Key changes:
- Architecture upgraded: sub-accounts do NOT log into Volcengine console
- Documented Ark API Key management via POST+JSON (verified working)
- Added chapter 12 (Ark API Key mgmt) and 13 (实测发现 with decisions)
- Fixed Step 1 code example to NOT create console login
- Updated core requirements table, architecture diagram, limitations
- All findings verified through actual API testing on 2026-03-20
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
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