The Subagents section of docs/plugins/hooks.md listed subagent_ended
but did not describe its payload. Plugin authors reaching for
agentId (as on subagent_spawned) silently got undefined because
PluginHookSubagentEndedEvent uses targetSessionKey as its identity
field and has no agentId/childSessionKey.
Document all fields from PluginHookSubagentEndedEvent and explicitly
note the missing identity fields so handlers can correlate events
correctly.
Closes#95186
Co-authored-by: MaHaoHao-ch <MaHaoHao-ch@users.noreply.github.com>
0374892fd8