Grok provider: multi-agent visibility via task.* events

[EnzoTironi]

Before submitting

• I searched existing issues and did not find a duplicate.
• I am describing a concrete problem or use case, not just a vague idea.

Area

apps/server

Problem or use case

Grok spawns in-process subagents (spawn_subagent tool_call). T3 does not show them as task rows; multi-agent work is invisible (V1 explicitly ignored child sessions — #3156).

Proposed solution

Map subagent tool calls to task.started / task.completed for parent-turn visibility without flattening child transcripts.

Why this matters

Users driving multi-agent Grok work cannot see spawned agents in the timeline the way Claude Task tools appear.

Smallest useful scope

Detector + task.* emit only. No child-session transcript merge.

Alternatives considered

Wait for orchestration v2 background-task model only — still need adapter mapping of the tool_call shape.

Risks or tradeoffs

Must use unique event stamps (not reuse tool-call stamp); dedupe per taskId; avoid false positives on tools whose description mentions "subagent".

Examples or references

PR #5425. Live verified 2026-08-05: tool title spawn_subagent.