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/auto-slash-command/hook.ts

@@ -5,6 +5,7 @@ import {
 } from "./detector"
 import { executeSlashCommand, type ExecutorOptions } from "./executor"
 import { log } from "../../shared"
+import { resolveSessionEventID } from "../../shared/event-session-id"
 import {
   AUTO_SLASH_COMMAND_TAG_CLOSE,
   AUTO_SLASH_COMMAND_TAG_OPEN,
@@ -25,16 +26,7 @@ function isRecord(value: unknown): value is Record<string, unknown> {
 }
 
 function getDeletedSessionID(properties: unknown): string | null {
-  if (!isRecord(properties)) {
-    return null
-  }
-
-  const info = properties.info
-  if (!isRecord(info)) {
-    return null
-  }
-
-  return typeof info.id === "string" ? info.id : null
+  return resolveSessionEventID(properties) ?? null
 }
 
 function getCommandExecutionEventID(input: CommandExecuteBeforeInput): string | null {
@@ -49,7 +41,7 @@ function getCommandExecutionEventID(input: CommandExecuteBeforeInput): string |
     "commandId",
   ]
 
-  const recordInput = input as unknown
+  const recordInput: unknown = input
   if (!isRecord(recordInput)) {
     return null
   }