Root cause: backend `/auth/logout` returns `{ success: true, data: null }`
(no business payload for a fire-and-forget endpoint). The previous
`AuthApi.logout` ran `unwrap(env)` (which passes null through, since
null is defined) and then `LogoutResponse.fromJson(null)`, which
Zod-parses as `z.object(...)` and throws "Invalid input: expected
object, received null".
The error was caught in `AuthRepository.logout` with
`console.warn(... clearing local anyway)` — logout actually still
worked (local clear ran), but a noisy red ZodError hit the console on
every logout click.
Fix: align `AuthApi.logout` with the existing fire-and-forget pattern
used by `register` and `sendCode` — call `httpClient` and ignore the
response body. Drop the now-unused `LogoutResponse` import.
`AuthRepository.logout` already discards the return value, so the
`Promise<LogoutResponse> → Promise<void>` signature change is safe.
Bundled in this commit (unrelated):
- chat-machine.actors.ts / user-machine.ts: removed stale design-doc
comment blocks (IDE/linter cleanup)
- user-machine.actors.ts: removed redundant `userStorage.clearUserData()`
from `userLogoutActor` — `authRepo.logout` already clears local
user data, so this was a no-op duplicate.
- sidebar-screen.tsx: removed one stale comment line.
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