Use owner enums for error and T-Bank protocol values with ESLint regression checks.
Preserve open wire fallbacks and keep protocol imports independent of DI and Prisma.
Verified npm ci, verify, 226 unit tests, 262 isolated e2e tests and unchanged OpenAPI.
Enable strict TypeScript and reject non-null and definite-assignment assertions. Declare externally populated DTO fields, preserve runtime validation, and narrow values at their owners.
Verified: backend verify (257 tests), unchanged OpenAPI, and 21 SQLite/HTTP tests on retry. The initial SQLite run had two timeouts; baseline HEAD passed 21 tests as well.
ksv741