The first v1.8.0 prod-deploy build job failed: `docker compose build` interpolates the
WHOLE compose file, and the backend's :?-guarded EXPORT_SIGN_KEY — added with the
finished-game export after the last prod release (v1.7.0), so the prod build never
exercised it — was absent from the build job's env, tripping the guard before any image
built. Prod was untouched (build-only failure: no image pushed, no deploy, no migration).
Add EXPORT_SIGN_KEY (audited every :?-guarded compose var against the build job env — it
was the only genuinely-missing one; TELEGRAM_MINIAPP_URL is derived in the run step).
Verified by reproducing the build-job env + `docker compose config`.
developer
Ilia Denisov