fix(background-agent): pass query directory to session.get in 4 call-sites (#2937)

resolveSubagentSpawnContext and related lookups called client.session.get
without the query.directory parameter, causing project-scoped sessions
to 404 under newer OpenCode SDK versions. Threaded directory through
SpawnerContext/BackgroundManager so all four call-sites pass it.

🤖 Generated with OhMyOpenCode assistance
https://github.com/code-yeongyu/oh-my-opencode

src/features/background-agent/session-existence.ts

@@ -35,9 +35,16 @@ function isSessionNotFoundError(error: unknown): boolean {
   return message.includes("not found") || message.includes("missing")
 }
 
-export async function verifySessionExists(client: OpencodeClient, sessionID: string): Promise<boolean> {
+export async function verifySessionExists(
+  client: OpencodeClient,
+  sessionID: string,
+  directory?: string
+): Promise<boolean> {
   try {
-    const response = await client.session.get({ path: { id: sessionID } })
+    const response = await client.session.get({
+      path: { id: sessionID },
+      ...(directory ? { query: { directory } } : {}),
+    })
 
     if (response.error !== undefined && response.error !== null) {
       return !isSessionNotFoundError(response.error)