# Theme-Aware Asset Switching

## Objective

Swap logos, screenshots, and illustrations so each one suits the surface it lands on.

A single asset reference that resolves to the correct light or dark variant at render time, with its dimensions reserved.

## Before You Begin

This feature is being added to an application that already exists and already
works. Do not scaffold a new project, and do not assume a blank slate.

Inspect the codebase first and establish:

- The existing application structure and where code of this kind already lives.
- The framework and version in use.
- The existing design system — colours, spacing, typography, and component conventions.
- Existing UI components you can reuse instead of writing new ones.
- The existing database structure, if this feature needs to persist anything.
- The existing authentication and authorization system, if this feature is user-scoped.
- Dependencies already installed, so you don't add a library that duplicates one.
- The existing test setup and conventions.

Only start writing code once you understand the above. If the application
already implements part of this feature, extend it rather than replacing it.

## Implementation Instructions

1. Find every raster and vector asset that assumes a background — logos with white knockouts, product screenshots, illustrations with dark line work, diagrams, empty-state artwork — and give each one a variant per theme.
2. Resolve the variant from the same source of truth the rest of the theme uses, so a single toggle switches the palette and the artwork together rather than leaving the logo a step behind.
3. Reserve each asset's dimensions in the layout before it loads, so swapping variants or waiting on a download never reflows the page around it.
4. Define what renders when a variant is missing: fall back to the light asset on a neutral plate rather than showing nothing, and make the gap visible in development so the missing file gets added.
5. Do not switch assets with a script that runs after the page has painted. The user sees a white logo flash on a dark page, and it happens on every navigation, which is exactly the moment people notice.

## UI and UX Requirements

Match the application's existing design system exactly. Reuse its components,
spacing, and typography. This feature should look like it was always there.

## Responsive Requirements

Works on mobile, tablet, and desktop. Touch targets are large enough to hit on a
phone, and nothing overflows horizontally at 320px.

## Accessibility Requirements

- Fully keyboard navigable.
- Correct semantic elements and ARIA roles.
- Visible focus states.
- Meets WCAG AA contrast.
- Dynamic changes are announced to screen readers.
- Respects prefers-reduced-motion.

## Edge Cases

- Resolving the variant on the client after first paint produces a visible flash of the wrong asset. Decide the theme before the markup is sent, or render both variants and let the stylesheet choose so nothing swaps after paint.
- An asset whose size is not reserved shifts every element below it when it loads or changes. Declare intrinsic dimensions or an aspect ratio on every themed asset.
- A missing dark variant must degrade to something readable rather than an empty frame or a broken image. A light asset on a neutral plate is acceptable; nothing at all is not.
- Server-rendered pages must produce the same variant the client would choose, or the first render will be corrected in front of the user. Where the theme is genuinely unknown at render time, use a mechanism that resolves without executing script.
- User-uploaded content has no themed variant and never will. Place it on a fixed neutral surface rather than trying to invert it.
- Printing and PDF export should use the light variants regardless of the active theme, because the output lands on white paper.
- The theme can change mid-session, from the system setting or another tab. Assets must follow that change without a reload.

## Testing

Exercise the feature end to end in the running application. Cover every edge case
above, then run the existing test suite and confirm nothing regressed.

## Acceptance Criteria

- [ ] Every background-dependent asset has a variant for each theme, referenced through one shared mechanism.
- [ ] No asset flashes the wrong variant on load, navigation, or theme change.
- [ ] Themed assets reserve their dimensions and cause no layout shift.
- [ ] A missing variant falls back to a legible asset rather than an empty space.
- [ ] Server-rendered output matches what the client resolves, with no visible correction after hydration.
- [ ] Printed and exported output uses the light variants.
- [ ] Changing the theme mid-session updates every asset without a reload.
- [ ] The feature matches the existing design system.
- [ ] No existing functionality is broken.

## Adaptation Rules

- Match the existing design system. Do not introduce a new colour palette,
  spacing scale, or component library.
- Reuse existing components and utilities wherever they fit.
- Follow the naming, file layout, and code style already present.
- Do not upgrade, replace, or remove existing dependencies to make this
  feature fit. Adapt the feature to the app, not the app to the feature.
- Do not break existing functionality. If a change is genuinely required in
  existing code, make the smallest one that works and say so.
- If something in these instructions conflicts with how the application is
  built, follow the application and explain the deviation.

## Final Verification

Before you report the work as done:

1. Re-read the acceptance criteria above and check each one against what you
   actually built.
2. Run the application and exercise the feature end to end.
3. Run the existing test suite and confirm you have broken nothing.
4. Check the feature on mobile, tablet, and desktop widths.
5. Check keyboard navigation and focus handling.
6. Summarize what changed: files added, files modified, and anything you
   deliberately did differently because of how this application is built.

If any acceptance criterion is unmet, fix it before reporting completion.