Pattern: Identifier-first auth

Universal — email (or username) step → adaptive credentials (sign-in / create / passkey).

Applies to Tasteful iOS (AuthenticationView), product web (LoginPageClient), and future Intrinsic apps with password/passkey auth.

Principles (non-negotiable)

Platform HIG beats custom chrome (principles/FOUNDATION.md) — native Form fields, editor sheets, toolbar Cancel, swipe-to-dismiss on iOS.
Sub-tasks are sheets (patterns/EDITOR_SHEET.md) — changing identity, reset password, or any “leave the default” flow is a modal with Cancel, not in-place layout morph on the parent.
Reversible by default — dismiss sheet = parent state unchanged (saved email chip still there).
Identifier-first copy — read-only email row shows trailing Change (opens sheet); VoiceOver / sheet context use Use a Different Email; not “Use Another Account” unless showing a multi-account list.
Trust — legal consent on email + create-account steps only; footnote/text-sm secondary tier, not caption/text-xs.

State	UI	Notes
No saved email	Email field on main + Continue	First launch
Saved email (returning)	Read-only row: email + trailing Change + Continue	First launch / email step only
Post sign-out	Credentials — passkey-first when account has enrolled passkeys + Use Password Instead; password-first when none; email row + Change; no auto Face ID	`preferIdentifierStepOnNextAuth` + `shouldUsePasskeyFirst`
Different email	`DifferentEmailEntrySheet` / web modal — Change opens sheet; Close restores parent
Credentials	Email row + Change + passkey (when offered) or password; Sign In with Passkey nudge when returning and device supports passkeys — direct ceremony; passkey-first layout only when passkeys enrolled
Forgot password	`ForgotPasswordView` sheet	Canonical specimen

× in top-trailing toolbar (AuthSheetDismissButton) — matches Settings, Account, compose sheets in Tasteful
Swipe down remains available
Not leading Close / Cancel text on dismiss-only sheets

See patterns/PRIMARY_ACTION.md (universal). Auth-specific specimens below.

One root Form — the only scroll container on AuthenticationView:

Hero — first Section row, .listRowBackground(.clear), centered (frame(maxWidth: .infinity))
Fields — authFormSections (native grouped rows)
Actions — glass Continue / Sign In in transparent list rows (not safeAreaInset, not sibling VStack)
Legal — Section footer on email + create-account steps

Simulators can lie; device-test after any auth layout change.

❌ .toolbarRole(.editor) on single-screen dismiss-only sheets — editor role expects Cancel + confirmation in the toolbar; otherwise iOS 26 may show spurious back chrome beside Cancel
❌ Form inside ScrollView on auth screens — email, password, and create-account fields collapse to zero height on device
❌ Sibling VStack + Form + .fixedSize(vertical:) on the main auth screen — Form reports zero height; fields disappear on device
❌ safeAreaInset pinning Continue — fights natural auth flow; CTA belongs in-form after fields
❌ Morph main auth layout when user changes email — always sheet/modal via Use a Different Email
❌ Hand-built rounded TextField chrome when Form works (use Form inside sheet; main email step may use plain field only when Form-in-ScrollView collapses — prefer chip + sheet instead)
❌ Skinny text-only “Back to …” as the only escape from a sub-task
❌ Clear parent email before user commits in sheet
❌ “Use Another Account” on single-saved-email chip

State	UI
Saved email	Row: email + trailing Change
Different email	Modal dialog with Cancel + backdrop dismiss
Legal	`APP_URLS` → `https://tasteful.to/terms`, `https://tasteful.to/privacy`

Compared to ForgotPasswordView / DifferentEmailEntrySheet sheet pattern
Sub-task dismiss restores parent without data loss
Copy synced iOS ↔ web (AuthCopy / AUTH_COPY)
No archive DESIGN_SYSTEM.md — Intrinsic Design repo + live site only
Device test: sign-out → passkey-first credentials → Change → dismiss → email restored