Use native Codex steering and transcript deletion

AGENTS.md

@@ -47,9 +47,10 @@ Module-by-module intent is in PLAN.md's "Backend layout".
   readiness poll watches the process as well as the port, since a model that
   will not load exits in a second and was being reported as "gave up after
   300s". See PLAN.md's "Transport" and "llama-server management".
-  Codex is `codex exec --json`, one child process per turn; its driver keeps
-  the thread id for `exec resume`, persists messages queued behind a turn, and
-  reads subscription limits through the CLI's app-server protocol.
+  Codex is one persistent `codex app-server --stdio` process per session; its
+  driver uses native turn steering and interruption, persists the protocol
+  state and thread id, and reads subscription limits through the same CLI
+  protocol.
 - `app/` — the Compose app, package `com.example.aiapp`, label "AI Sessions".
   `AppRoot.kt` is the navigation `when`; `MainScreen.kt` the root's four tabs
   (sessions, import, models, setups); `Api.kt`/`EventStream.kt` the REST + SSE