chore(ai-sdks): Document gen_ai.function_id use as agent name fallback

Author: alexander-alderman-webb

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

@@ -25,7 +25,7 @@ Agent invocations represent operations that can include multiple model calls, or
 - Span `op` **SHOULD** be `"gen_ai.invoke_agent"`.
 - Span `name` **SHOULD** be `"invoke_agent {gen_ai.agent.name}"`. (e.g. `"invoke_agent Weather Agent"`) **[4]**
 - Attribute `gen_ai.operation.name` **MUST** be `"invoke_agent"`.
-- Attribute `gen_ai.agent.name` **SHOULD** be set to the agent's name. (e.g. `"Weather Agent"`)
+- Attribute `gen_ai.agent.name` **SHOULD** be set to the agent's name. (e.g. `"Weather Agent"`). As a fallback to `gen_ai.agent.name`, the product also interprets `gen_ai.function_id` as an agent name for libraries that let users set a tracing identifier on a per-invocation basis.
 - If relevant, the `gen_ai.pipeline.name` attribute **SHOULD** be set to the name of the AI workflow, pipeline or chain within which the agent operates. (e.g. `"weather-pipeline"`)
 
 Additional attributes on the span:
@@ -53,7 +53,7 @@ This span represents a request to an AI model or service that generates a respon
 - Attribute `gen_ai.provider.name` **MUST** be the Generative AI product as identified by the client or server instrumentation. (e.g. `"openai"`)
 - Attribute `gen_ai.request.model` **MUST** be the requested model. (e.g. `"gpt-4o"`)
 - Attribute `gen_ai.response.model` **MUST** be the concrete response model. (e.g. `"gpt-4o-2024-08-06"`)
-- If the request originates from an agent, the `gen_ai.agent.name` attribute **SHOULD** be set to the name of the agent. (e.g. `"Weather Agent"`)
+- If the request originates from an agent, the `gen_ai.agent.name` attribute **SHOULD** be set to the name of the agent. (e.g. `"Weather Agent"`). As a fallback to `gen_ai.agent.name`, the product also interprets `gen_ai.function_id` as an agent name for libraries that let users set a tracing identifier on a per-invocation basis.
 - If relevant, the `gen_ai.pipeline.name` attribute **SHOULD** be set to the name of the AI workflow, pipeline or chain within which the agent operates. (e.g. `"weather-pipeline"`)
 
 Additional attributes on the span:
@@ -111,7 +111,7 @@ Describes a tool execution.
 - Span `name` **SHOULD** be `"execute_tool {gen_ai.tool.name}"`. (e.g. `"execute_tool query_database"`)
 - Attribute `gen_ai.operation.name` **MUST** be `"execute_tool"`.
 - Attribute `gen_ai.tool.name` **SHOULD** be set to the name of the tool. (e.g. `"query_database"`)
-- Attribute `gen_ai.agent.name` **SHOULD** be set to the name of the agent that invoked the tool. (e.g. `"Weather Agent"`)
+- Attribute `gen_ai.agent.name` **SHOULD** be set to the name of the agent that invoked the tool. (e.g. `"Weather Agent"`). As a fallback to `gen_ai.agent.name`, the product also interprets `gen_ai.function_id` as an agent name for libraries that let users set a tracing identifier on a per-invocation basis.
 - If relevant, the `gen_ai.pipeline.name` attribute **SHOULD** be set to the name of the AI workflow, pipeline or chain within which the agent operates. (e.g. `"weather-pipeline"`)
 
 Additional attributes on the span: