AI-103: Developing AI Apps and Agents on Azure

In Microsoft Foundry's OpenTelemetry-based agent tracing, a trace consists of spans that can be nested as parent/child spans, forming a hierarchical tree that reflects the full call stack of an agent run — including sub-agent calls and tool invocations. This hierarchical span structure is what allows capture of all nested operations across an entire agent run, and is rendered as a hierarchical trajectory/tree in the Foundry portal's Observability > Traces view. Separately, each tool-call span carries attributes (metadata) that record the tool's invocation arguments and returned results, following OpenTelemetry semantic conventions for tool calls, which makes this data queryable and auditable. KQL query filters and sampling/trace sampling policies relate to querying stored telemetry or controlling which traces are collected, not to the structural capture of nested operations or the recording of tool call inputs/outputs.