ai.newnal.illi.account.exchangeCode

Exchange the one-time code from a client=native sign-in (delivered to the app at …/native/callback?code=…, 60 s, single use) for a session token, sent afterwards as Authorization: Bearer on every call and on /events. The code is bound to the code_challenge the app sent when it started the sign-in; codeVerifier proves it is the same app (PKCE-style S256), which stops a code obtained for another account from being injected into the app.