Users need guidance on when to use --rollout-external-engine-addrs, when to stay with --sglang-config, and which weight-update path (full disk/delta NCCL) to pick for external deployments. This documentation serves as a roadmap to help make those decisions.

Read if you are considering external rollout engines or need to choose between --sglang-config and --rollout-external-engine-addrs.

1. Created English and Chinese versions of external-rollout-engines.md with a decision table, explanations of external engines, and relationships with sglang-config. 2. Modified delta-weight-sync.md (EN/ZH) to add a reference to the Cursor Composer 2 technical report. 3. Modified sglang-config.md (EN/ZH) to add a cross-link to the external-rollout-engines page. 4. Updated index.rst (EN/ZH) and README (EN/ZH) to include the new page in the table of contents and start-by-use-case section.

Documentation-only change with no code modifications. Low risk; the author implemented the related features and is familiar with the system. Potential minor risk if users follow incorrect advice, but the content was reviewed before merge.

Positive impact on user experience for those deploying external rollout engines. No impact on system behavior or performance.