Connect sign-up to Sendico Facts intake (#46)

docs/implementation.md

@@ -828,3 +828,55 @@ existing mount requires reauthentication at its new cookie path. Notification
 activation URLs remain configured frontend URLs. No live deployment, optional
 security scans or merge were performed. The unrelated local notifications sender
 configuration remains uncommitted. See [API version installation](api-versions.md).
+
+## Sign-up Facts intake — task #46
+
+[Task #46](https://git.sendico.io/tech/sxchnge/issues/46), branch
+`identity-facts-46`, connects the product sign-up service to Sendico's public
+individual registry and immutable Facts intake through optional `api.sendico`
+configuration. Owner: `tech`; project: SXCHNGE; labels: backend and frontend.
+
+The adapter sends full name, normalized email and the local customer reference.
+The BFF persists a customer-owned subject binding, immutable facts snapshot and
+confirmed receipt before activation email or sign-up acceptance. Activation and
+resend enforce the handoff. The shared database source can require majority
+writes and primary majority reads without bypassing its connection/transaction
+lifecycle. Initial account/token creation remains atomic and uses a secret-derived
+activation key, allowing same-key recovery after an intake outage without an
+extra cooldown for an unsent token. Archived customers cannot resume sign-up.
+
+Backend and frontend completion reviews covered the full task contribution,
+including the public contracts, customer ownership, stable replay namespace,
+concurrent claims, error classification, credential handling, logging, metrics and
+DTO/mapper/service/model/provider separation. UX review preserved input, loading
+suppression and confirmation-based success. Typed support guidance reaches both
+sign-up and verification resend/confirmation through the shared auth package;
+EN/RU feedback preserves live-region semantics and existing responsive controls.
+The new localized widget fixture initially double-disposed the app-owned locale
+provider; the fixture ownership was corrected. Focused integration tests also
+exposed the initial-token cooldown issue, which was fixed in the creation flow.
+
+Individual registration is not idempotent upstream. A durable claim prevents
+speculative repeat registration after an ambiguous result; reconciliation uses
+the saved request reference and authoritative Sendico records. Intake replay is
+safe after receipt loss and retains original assertions. Actual provider IDs,
+the endpoint and a same-account Vault-rendered access token must be provisioned
+before enabling this integration. Tests use simulated HTTP and disposable MongoDB;
+no live provider resources, live email, deployment, merge or optional security
+scan is part of this delivery. The unrelated notifications runtime configuration
+is excluded. Configuration, rollout, telemetry and recovery details are in
+[Sign-up Facts intake](signup-facts.md).
+
+Final validation passed: `GOFLAGS=-p=2 make test` (all backend race tests and
+`make test-frontend` suites), `make lint-backend`,
+`dart format --output=none --set-exit-if-changed` for all 11 changed Dart files,
+and `flutter analyze` in `frontend/app` and `frontend/packages/sxchnge_auth`.
+Focused Go race suites and Flutter backend/provider/widget tests also passed;
+the diagnostic public API run
+`go -C backend/product test -race -v ./auth/http/v1/public -count=1 -timeout=90s`
+passed. The initial unrestricted `make test` failed when Testcontainers could
+not start its reaper before the Mongo fixture deadline. Lower Go package
+parallelism resolved that infrastructure contention. The next full run exposed
+the new locale fixture disposal error noted above; the corrected final run
+passed, including EN/RU support states and verification recovery. No checks were
+weakened or unrelated work changed.