fix: use separate taskID for title generation to prevent model leak (#6552)

ensureTitle was sending small-model requests with the same HEADER_TASKID
as the agent session. The gateway saw two different models (kilo-auto/small
and kilo-auto/frontier) under the same task and routed to both. Prefixing
the title sessionID with "title-" isolates it from the agent task.

packages/opencode/src/session/prompt.ts

@@ -1993,7 +1993,7 @@ NOTE: At any point in time through this workflow you should feel free to ask the
       tools: {},
       model,
       abort: new AbortController().signal,
-      sessionID: input.session.id,
+      sessionID: `title-${input.session.id}`, // kilocode_change - separate taskID to prevent small-model leak (#6552)
       retries: 2,
       messages: [
         {