Inconsistent Message/Prompt Types Across Client, Chat, and Context Modules

Currently, there are inconsistencies in how message and prompt data structures are defined and handled across the client, chat (`chat_session`), and context modules. These modules are core to message processing, and type mismatches here can lead to bugs and integration problems. Specifically, the types used for messages and prompts might not be fully consistent, making it harder to ensure smooth data flow.

**Proposed Solution:**

To improve consistency and reduce potential errors, we should standardize the types used for messages and prompts across the client, chat (`chat_session`), and context modules. We will use the message models defined in `src/models` as a **reference** for this standardization.

This involves:

1. **Reviewing Message/Prompt Handling:** Examine how messages and prompts are represented and passed between the client, chat (`chat_session`), and context modules.
2. **Referencing `src/models`:** Compare the existing types with the message models in `src/models` (e.g., `Message` class).
3. **Achieving Consistency:** Adjust type definitions in the client, chat, and context modules to align with the structure and fields defined in `src/models` as closely as reasonably possible, especially for core message attributes (role, content, etc.). We are aiming for *consistency* inspired by `src/models`, not necessarily a strict one-to-one mapping of every type.
4. **Type Hinting:** Ensure clear and consistent type hinting is used in these modules to reflect the standardized message/prompt types.

**Acceptance Criteria:**

* Message and prompt types are demonstrably more consistent across the client, chat, and context modules.
* `src/models` serves as a clear reference point for message structure.
* Code in these modules exhibits improved type clarity and consistency in message handling.