Ability to open sub-agent sessions in chat

[dobesv]

When viewing a chat session with sub-agent calls, a new "open in tab" icon button will show.

Clicking the button looks up the session ID of the sub-agent session and opens it in a new tab.

To support this:

• the python agent was updated to propagate the parent user ID, session ID, and tool call ID into the child task information as metadata field kagent_user_id, kagent_caller_session_id, and kagent_caller_tool_call_id
• parent user_id is also used in child session so that the user has permission to see those sessions
• an endpoint was added to the go server to lookup a child session ID by finding the task with the matching parent session ID and tool call and using the session ID from that task to identify the session

A side-effect of this change is that if you click an agent you can now see the sub-agent sessions listed there as if they were your own chats. Personally I prefer it, but if this is a problem we could look for a way to hide those, maybe filter out sub-agent sessions on that list based on the metadata fields we use to find sub-agent sessions.

Signed-off-by: Dobes Vandermeer dobes.vandermeer@newsela.com

[Copilot]

Pull request overview

Adds end-to-end support for opening sub-agent chat sessions from a parent chat by correlating agent tool calls to the spawned child session, using propagated metadata and a new backend lookup endpoint.

Changes:

• UI: Passes parent sessionId down to agent tool call rendering and adds an “open in tab” button that looks up and opens the sub-agent session.
• Python (kagent-adk/core): Propagates caller metadata (session/tool-call identifiers + user identity) across A2A boundaries and injects it into child task metadata via a new plugin + request metadata provider.
• Go (core): Adds GET /sessions/{session_id}/subagentsessions/{tool_call_id} and database lookup logic to resolve a child session ID from task metadata; includes tests.

Reviewed changes

Copilot reviewed 20 out of 20 changed files in this pull request and generated 9 comments.

Show a summary per file

File	Description
ui/src/components/chat/ToolCallDisplay.tsx	Threads sessionId into AgentCallDisplay.
ui/src/components/chat/ChatMessage.tsx	Adds sessionId prop and passes it to tool-call rendering.
ui/src/components/chat/ChatInterface.tsx	Provides the active session id down to message rendering.
ui/src/components/chat/AgentCallDisplay.tsx	Adds “open in tab” button that fetches sub-agent session ID and opens it.
ui/src/app/actions/sessions.ts	Adds getSubAgentSession action calling the new backend endpoint.
python/packages/kagent-core/src/kagent/core/a2a/_consts.py	Introduces constants for caller metadata keys/prefix.
python/packages/kagent-core/src/kagent/core/a2a/init.py	Exposes new caller metadata constants via module imports.
python/packages/kagent-adk/src/kagent/adk/types.py	Adds A2A request metadata provider and wires it into RemoteA2aAgent.
python/packages/kagent-adk/src/kagent/adk/converters/event_converter.py	Includes kagent_* state metadata in emitted event metadata.
python/packages/kagent-adk/src/kagent/adk/_agent_executor.py	Applies propagated user_id and persists kagent_* metadata into task metadata.
python/packages/kagent-adk/src/kagent/adk/_session_linking_plugin.py	New plugin that injects parent session/tool-call metadata into session state before AgentTool runs.
python/packages/kagent-adk/src/kagent/adk/cli.py	Registers SessionLinkingPlugin alongside STS integration.
python/packages/kagent-adk/tests/unittests/converters/test_event_converter.py	Updates mock invocation context to include session.state.
go/core/internal/httpserver/server.go	Registers new sub-agent session lookup route.
go/core/internal/httpserver/handlers/sessions.go	Adds handler to resolve child session and return session info.
go/core/internal/httpserver/handlers/sessions_test.go	Adds handler tests for the new endpoint.
go/api/database/client.go	Extends DB client interface with GetSubAgentSession.
go/core/internal/database/client.go	Implements DB query to find child session via task metadata.
go/core/internal/database/fake/client.go	Implements in-memory GetSubAgentSession for handler tests.
go/core/internal/database/client_test.go	Adds DB-level test for GetSubAgentSession.

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