Two paired changes that finally make the Codex parallel-calls fan-out
visible as actual clickable tabs in the chat surface, plus a credit-
free spoof that lets the whole pipeline run in dev / CI without ever
touching the upstream API.
1. Real tab UI (frontend).
The chat-adapter used to render the per-worker outputs as inline
`[Codex tab 1/N] ...` text blocks in the assistant message body,
which collapsed into one big run-on block once more than a handful
of tokens had streamed. Now each `codex_*` SSE event is folded into
`codexParallelState` and re-published as the `args.state` of a
single tool-call part with `toolName === "codex_parallel"`. The
assistant-ui surface dispatches that to the new
`CodexParallelToolUI` wrapper, which mounts the existing
`CodexParallelTabs` component -- one tab per worker, one Synthesis
tab, click to switch. The stable `toolCallId` keeps assistant-ui
updating the SAME card across stream yields rather than spawning
new cards.
`renderCodexTabsBlock` now returns the empty string so the message
body no longer contains the labelled-text fallback (kept the
function name so the rest of the adapter's `renderFullContent` /
pin-signature paths are untouched).
2. Credit-free Codex SDK spoof (backend).
New `studio/backend/core/inference/codex_spoof.py` exposes a drop-in
subset of the upstream `openai_codex` surface (`AsyncCodex`,
`AppServerConfig`, `ApprovalMode.deny_all`, `SandboxMode.read_only`,
thread with `turn().stream()` + `run_streaming()` + `run()`) and
emits deterministic per-tab streaming events tagged with the worker
index, so flipping between tabs in the UI shows visibly distinct
text. Activated by `UNSLOTH_CODEX_SPOOF=1`; `_import_codex` installs
the spoof into `sys.modules` under both `openai_codex` and
`codex_app_server` and the rest of the provider keeps running
unchanged. OFF by default; production is unaffected.
Six new tests cover the spoof itself (module install, env-flag
gating, delta + completion event shape, per-tab tagging, provider
import path, safety-kwargs resolution against the spoof). 69/69
tests pass with and without the flag; TypeScript clean.
