feat(pi): add Codex fast mode extension

pi/extensions/openai-codex-fast/state.ts

@@ -0,0 +1,53 @@
+export const FAST_STATE_ENTRY = "openai-codex-fast";
+
+export type FastCommand = "toggle" | "on" | "off" | "status";
+
+type ModelIdentity = { provider: string; api: string; id: string };
+
+export function parseFastCommand(args: string): FastCommand | undefined {
+  const command = args.trim().toLowerCase();
+  if (command === "") return "toggle";
+  if (command === "on" || command === "off" || command === "status") return command;
+  return undefined;
+}
+
+export function isCodexModel(model: ModelIdentity | undefined): boolean {
+  return model?.provider === "openai-codex" && model.api === "openai-codex-responses";
+}
+
+export function restoreFastMode(branch: readonly unknown[]): boolean {
+  let enabled = false;
+  for (const entry of branch) {
+    if (
+      typeof entry !== "object" || entry === null ||
+      !("type" in entry) || entry.type !== "custom" ||
+      !("customType" in entry) || entry.customType !== FAST_STATE_ENTRY ||
+      !("data" in entry)
+    ) continue;
+    const data = entry.data;
+    if (
+      typeof data === "object" && data !== null &&
+      "enabled" in data && typeof data.enabled === "boolean"
+    ) enabled = data.enabled;
+  }
+  return enabled;
+}
+
+export function patchFastPayload({
+  enabled,
+  model,
+  payload,
+}: {
+  enabled: boolean;
+  model: ModelIdentity | undefined;
+  payload: unknown;
+}): unknown {
+  if (
+    !enabled || !isCodexModel(model) ||
+    typeof payload !== "object" || payload === null || Array.isArray(payload) ||
+    !("model" in payload) || payload.model !== model?.id ||
+    !("input" in payload) || !Array.isArray(payload.input)
+  ) return undefined;
+
+  return { ...payload, service_tier: "priority" };
+}