refactor(session): separate streaming message updates from modifyMessage (#571)

* refactor(session): add dedicated streaming message update functions

* refactor(session): replace modifyMessage with dedicated streaming functions in orchestration

Ultraworked with [Sisyphus](https://github.com/code-yeongyu/oh-my-Claude)

Co-authored-by: Sisyphus <clio-agent@sisyphuslabs.ai>

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Co-authored-by: Sisyphus <clio-agent@sisyphuslabs.ai>
(cherry picked from commit d4a5a92a6add330ec1a61c1ddd0017fd3854e940)