Now I remember the theme

openspec/specs/site-theming/spec.md

@@ -33,6 +33,30 @@ Persistence MUST be stored locally in the browser (e.g., localStorage).
 - **WHEN** the user selects `light` theme and reloads the page
 - **THEN** the `light` theme remains active
 
+### Requirement: Theme persistence works across visits with fallback
+The site MUST persist the user's theme selection across visits so returning users see the last-selected theme.
+
+The site MUST use client-side persistence and MUST support a fallback mechanism:
+- Primary: `localStorage`
+- Fallback: a client-side cookie
+
+The effective theme selection order MUST be:
+1) Stored theme in `localStorage` (if available)
+2) Stored theme in a cookie (if localStorage is unavailable)
+3) Default selection using environment signals
+
+#### Scenario: LocalStorage persists across a later visit
+- **WHEN** a user selects `light` theme and later returns to the site in the same browser
+- **THEN** the site initializes in `light` theme before first paint
+
+#### Scenario: Cookie fallback is used when localStorage is unavailable
+- **WHEN** the browser environment blocks `localStorage` access and the user selects `dark` theme
+- **THEN** the theme is persisted using a client-side cookie and is restored on the next visit
+
+#### Scenario: No persistence available falls back to defaults
+- **WHEN** both `localStorage` and cookie persistence are unavailable
+- **THEN** the site falls back to default theme selection using environment signals
+
 ### Requirement: Default theme selection
 If the user has not explicitly selected a theme, the site MUST choose a default theme using environment signals.