Record the execution platform (kind vk|telegram|direct + device subtype
ios|android|web) on each session, captured at creation and carried
gateway->backend as a trusted X-Platform header, so the upcoming
store-compliance gate has an unforgeable execution context.
- backend.sessions gains nullable platform_kind/platform_subtype columns
(migration 00011, CHECK-constrained, jet regenerated); session.Platform
captures them at mint, resolve returns them, middleware exposes platform(c).
kind is derived from the establish endpoint, never a client field; the
account-merge session mint inherits the caller's platform.
- gateway derives the platform (VK subtype from the signed vk_platform via
vkauth, Telegram/direct best-effort from the client) and injects X-Platform
on every authenticated backend call through the request context.
- ui submits a best-effort device subtype on the telegram/guest/email login
requests (new FBS subtype field); VK is server-derived from the signed params.
- an unattributed session is untrusted (view-only); VK/TG self-heal on the next
cold-start re-mint, direct/email on re-login.
Signal plumbing only, no user-visible change; X-Platform is inert until the
gate consumes it.
Ilia Denisov