ref(ai-agents-sdks): Document input truncation (#16548)

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Document input truncation required for no information to be lost. All
client spans together should be sufficient to reconstruct the message
history.

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Author: alexander-alderman-webb

develop-docs/sdk/telemetry/traces/modules/ai-agents.mdx

@@ -48,7 +48,7 @@ Additional attributes on the span:
 
 | Attribute                          | Type   | Requirement Level | Description                                                                                                                             | Example                                                               |
 | :--------------------------------- | :----- | :---------------- | :-------------------------------------------------------------------------------------------------------------------------------------- | :-------------------------------------------------------------------- |
-| `gen_ai.input.messages`            | string | optional          | List of dictionaries describing the messages (prompts) given to the agent. **[0]**, **[1]**                                             | `'[{"role": "user", "parts": [{"type": "text", "content": "..."}]}]'` |
+| `gen_ai.input.messages`            | string | optional          | List of dictionaries describing the messages (prompts) given to the agent. **[0]**, **[1]**, **[6]**                                            | `'[{"role": "user", "parts": [{"type": "text", "content": "..."}]}]'` |
 | `gen_ai.tool.definitions`          | string | optional          | List of dictionaries describing the available tools. **[0]**                                                                            | `'[{"name": "random_number", "description": "..."}, ...]'`            |
 | `gen_ai.system_instructions`       | string | optional          | The system instructions passed to the model.                                                                                            | `"You are a helpful assistant."`                                      |
 | `gen_ai.request.max_tokens`        | int    | optional          | Model configuration parameter.                                                                                                          | `500`                                                                 |
@@ -113,7 +113,7 @@ Additional attributes on the span:
 
 | Attribute                          | Type   | Requirement Level | Description                                                                                                                          | Example                                                               |
 | :--------------------------------- | :----- | :---------------- | :----------------------------------------------------------------------------------------------------------------------------------- | :-------------------------------------------------------------------- |
-| `gen_ai.input.messages`            | string | optional          | List of dictionaries describing the messages (prompts) sent to the LLM. **[0]**, **[1]**                                             | `'[{"role": "user", "parts": [{"type": "text", "content": "..."}]}]'` |
+| `gen_ai.input.messages`            | string | optional          | List of dictionaries describing the messages (prompts) sent to the LLM. **[0]**, **[1]**, **[6]**                                             | `'[{"role": "user", "parts": [{"type": "text", "content": "..."}]}]'` |
 | `gen_ai.tool.definitions`          | string | optional          | List of dictionaries describing the available tools. **[0]**                                                                         | `'[{"name": "random_number", "description": "..."}, ...]'`            |
 | `gen_ai.system_instructions`       | string | optional          | The system instructions passed to the model.                                                                                         | `"You are a helpful assistant."`                                      |
 | `gen_ai.request.max_tokens`        | int    | optional          | Model configuration parameter.                                                                                                       | `500`                                                                 |
@@ -239,3 +239,8 @@ Some attributes are common to all AI Agents spans:
 | `"openai"`          | OpenAI                            |
 | `"perplexity"`      | Perplexity                        |
 | `"xai"`             | xAI                               |
+
+**[6]**
+
+The input list should include the most recent messages up to and including the most recent previous model response. The previous model response is identified with an "assistant" or "model" role in common frameworks. If there is no previous model response in the input list, then all input items which are not system instructions should be included. System instructions must be added in `gen_ai.system_instructions`, and are not included in the `gen_ai.input.messages` list.
+