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/hooks/compaction-context-injector/session-id.ts

@@ -1,8 +1,9 @@
+import { resolveSessionEventID } from "../../shared/event-session-id"
+
 export function isCompactionAgent(agent: string | undefined): boolean {
   return agent?.trim().toLowerCase() === "compaction"
 }
 
 export function resolveSessionID(props?: Record<string, unknown>): string | undefined {
-  return (props?.sessionID ??
-    (props?.info as { id?: string } | undefined)?.id) as string | undefined
+  return resolveSessionEventID(props)
 }