## What changed
- Add `additional_developer_instructions` to managed requirements and expose it through `configRequirements/read` as `additionalDeveloperInstructions`, independently of ordinary developer instructions.
- Include the managed instructions in model context, emit explicit replacement or removal messages when requirements change, and preserve the current value across compaction, resume, and agent forks without duplication.
- Reject managed instructions whose rendered context exceeds 10,000 estimated tokens.
## Testing
- Cover requirements layering and API serialization, context updates and removal, size validation, repeated model requests, compaction and resume, rollout migration, and agent forks.
GitOrigin-RevId: bc0b70fb7988944c2f68176dff55f5ed61eb46c8
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