Pattern: Primary action (forms)

Universal — every product, every platform. Auth is one consumer; compose sheets, onboarding, and settings forms follow the same rules.

Rule

Primary actions stay visually enabled. Validate on tap. Explain failures inline.

Disable a primary control only when the action is impossible — not when the user simply hasn’t finished typing.

Why (iOS 26+ Liquid Glass)

.glassProminent + .disabled washes out to low-contrast grey-on-grey. It reads as broken UI, not “waiting for input.” That violates Accessibility and Clarity first (principles/FOUNDATION.md).

Apple’s modern form pattern: enabled-looking primary + feedback on submit. Live requirement rows (checkmarks) are fine for multi-field sign-up.

iOS

// ✅ Primary glass — always full strength; validate in action
Button("Continue") { submit() }
    .buttonStyle(.glassProminent)
    .tint(accent)
    .disabled(isLoading)  // in-flight only

private func submit() {
    guard isValid else {
        inlineMessage = "Enter a valid email address."
        return
    }
    inlineMessage = nil
    // …
}

// ✅ Loading — same footprint as idle
Button { submit() } label: {
    GlassProminentButtonLabel(title: "Sign In", isLoading: isLoading)
}
.buttonStyle(.glassProminent)
.tint(accent)
.disabled(isLoading)

// ❌ Do not — pill shrinks to spinner width
if isLoading { ProgressView() } else { Text("Sign In").frame(maxWidth: .infinity) }

// ❌ Do not — illegible on device
.disabled(!isValidEmail)

• Inline errors: .footnote, .red or semantic error role
• Loading: keep the full-width glass pill — hide title with opacity(0) and center ProgressView in a ZStack (GlassProminentButtonLabel); never swap label for spinner alone (pill collapses)
• Placement: directly under the field — Section footer in Form; grouped custom fields use a VStack footnote below the control (never between field block and primary button)
• VoiceOver: field accessibilityHint + UIAccessibility.post(.announcement) on submit failure
• Shape: voice/COPY_STANDARDS.md (what happened + what to do)

Web

• Primary button stays full opacity; disabled only while loading
• Invalid submit → role="alert" message adjacent to the field or button
• Do not rely on disabled:opacity-45 as validation UX for primary CTAs

Relationship to other patterns

Specimens (Tasteful)

• AuthenticationView — Continue / Sign In
• DifferentEmailEntrySheet — sheet Continue
• ForgotPasswordView — Send Reset Link