fix(plugin): normalize event session ids

Handle OpenCode session events that carry the session ID under properties.info.id or properties.info.sessionID so background tasks and continuation hooks do not miss idle/error/delete events.

Add regression coverage for nested session.idle events completing background tasks and waking continuation hooks.

src/plugin/session-status-normalizer.ts

@@ -1,3 +1,5 @@
+import { resolveSessionEventID } from "../shared/event-session-id"
+
 type EventInput = { event: { type: string; properties?: Record<string, unknown> } }
 type SessionStatus = { type: string }
 
@@ -10,7 +12,7 @@ export function normalizeSessionStatusToIdle(input: EventInput): EventInput | nu
 	const status = props.status as SessionStatus | undefined
 	if (!status || status.type !== "idle") return null
 
-	const sessionID = props.sessionID as string | undefined
+	const sessionID = resolveSessionEventID(props)
 	if (!sessionID) return null
 
 	return {