ParentToolCallId obsolete

[IeuanWalker]

Sorry @SteveSandersonMS creating a new one for this #1148 as i cant reopen it and dont want it getting lost.

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Upgrading from 0.2.2 to 0.3.0 and im getting a warning that ParentToolCallId is obsolete - This member is deprecated and will be removed in a future version..

There isnt anything in the docs/ release notes about it, but what is the recommended way to link message/ and tool calls to subagent?

As in my UI I currently link messages and tool calls to their parent to create a live running tree -

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As mentioned on the other issue a new property has been added called AgentId but it doesn't look like that's been propagated down to anything.

Currently, I'm using ParentToolCallId in 2 places -

• From AssistantMessageEvent where the ParentToolCallId is within its data property AssistantMessageData
• From ToolExecutionStartEvent where the ParentToolCallId is within its data property ToolExecutionStartData

Neither of the above has an AgentId property

Looking at the source code looks like AgentId has only been added to SystemNotificationAgentCompleted and SystemNotificationAgentIdle

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Im using the .NET SDK

[github-actions]

Investigation Findings

This is a confirmed bug in the .NET SDK code generation.

What I investigated

• dotnet/src/Generated/SessionEvents.cs — the generated event types
• nodejs/src/generated/session-events.ts — the equivalent Node.js generated types (for comparison)
• The base SessionEvent class in the .NET SDK

What I found

In the Node.js SDK, every event interface has an agentId?: string property at the top level (directly on the event, not nested inside data), documented as:

Sub-agent instance identifier. Absent for events from the root/main agent and session-level events.

This agentId on the event object is the correct replacement for parentToolCallId (which is @deprecated in the data sub-objects in Node.js too).

In the .NET SDK, however:

• ParentToolCallId in data classes (AssistantMessageData, ToolExecutionStartData, etc.) was correctly marked [Obsolete]
• But AgentId was never added to the SessionEvent base class or any of the derived event classes (only SystemNotificationAgentCompleted and SystemNotificationAgentIdle got AgentId)

This means .NET consumers were left with a deprecated API and no valid replacement — the codegen missed propagating AgentId to the session event classes.

Root cause

The .NET code generation script did not add AgentId to the SessionEvent base class (or individual event classes) when parentToolCallId was deprecated in the schema. The fix should add AgentId (with the description "Sub-agent instance identifier. Absent for events from the root/main agent and session-level events.") to the .NET SessionEvent base class — matching the Node.js SDK's structure.

This is labeled as a bug.

Generated by Bug Handler for issue #1169 · ● 512.2K · ◷

[IeuanWalker]

Just to confirm what copilot found, the equivalent models in JS does have the agentId property

• AssistantMessageEvent -

  copilot-sdk/nodejs/src/generated/session-events.ts

  Line 1807 in fd16c3d

  agentId?: string;

• ToolExecutionStartEvent -

  copilot-sdk/nodejs/src/generated/session-events.ts

  Line 2278 in fd16c3d

  agentId?: string;

Missing from the equivalent .net models + not on the SessionEvent base class -

copilot-sdk/dotnet/src/Generated/SessionEvents.cs

Line 102 in c63feb2

public partial class SessionEvent