## What changed
Move `ExecServerProcess` into `core_test_support::exec_server` and update the sandbox, plugin, access, and turn-input tests to use it. Preserve the fixture's startup timeout, temporary `CODEX_HOME`, WebSocket URL discovery, and child-process cleanup.
GitOrigin-RevId: 152de3a83f4ad39e2c1223e15438608dba452850