Function readSubagentTurns

readSubagentTurns(
projectDir: string,
sessionId: string,
): AsyncGenerator<{ agentId: string; turn: MessageEntry }>
Streams the subagent turns spawned by a session, one at a time.

Recursively scans <sessionId>/subagents/agent-<agentId>.jsonl files (CC ≥ 2.1.2), including nested layouts (e.g. subagents/workflows/<runId>/agent-<id>.jsonl), and yields each user/assistant turn tagged with its agentId. Memory stays bounded — the consumer can group, filter, or process incrementally.

Yields nothing if the session has no subagents/ directory.
Parameters
- projectDir: string
  Absolute path to the project directory under ~/.claude/projects/<slug>/
- sessionId: string
  UUID of the parent session (without .jsonl extension)
Returns AsyncGenerator<{ agentId: string; turn: MessageEntry }>
Example
```
// Group by agent — typical use case
const byAgent = new Map<string, MessageEntry[]>();
for await (const { agentId, turn } of readSubagentTurns(dir, id)) {
  if (!byAgent.has(agentId)) byAgent.set(agentId, []);
  byAgent.get(agentId)!.push(turn);
}
```
- Defined in parser/session.ts:128