# Content Security Policy

## Objective

Cut script-injection risk with a policy the existing app can actually run under.

A CSP built from an inventory of what the app really loads, rolled out in report-only mode before it is enforced.

## 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. Inventory first: every inline script and style, every third-party origin, every worker, frame, font, and image host the app loads. Report that list before writing a single directive.
2. Add a per-response nonce to the inline scripts you must keep, and hashes for the ones you cannot make dynamic.
3. Deploy in report-only mode, collect violations from real traffic for long enough to cover the slow paths, and only then enforce.
4. Set a violation report endpoint that deduplicates by directive and blocked URI, so one broken third-party script does not produce a million rows.
5. Do NOT reach for unsafe-inline or unsafe-eval to make the errors stop. A policy with unsafe-inline on script-src provides essentially none of the protection you added it for.

## 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

- Asset hosts, API origins, and analytics domains differ between development, staging, and production — generate the policy per environment.
- Browser extensions inject scripts and will generate violation reports you cannot fix. Filter them out or they will drown the real signal.
- Some third-party scripts load further scripts at runtime; the origin you allowlist is rarely the only one they need.
- Violation reports can include URL fragments and query strings — strip anything sensitive before storing them.
- The nonce must be unique per response and never cached; a cached page with a stale nonce blocks its own scripts.
- Blocked content usually fails silently for the user. Watch error rates as well as reports when you flip to enforcing.

## 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

- [ ] The policy is derived from an inventory of actual app dependencies.
- [ ] Inline scripts use per-response nonces or hashes; unsafe-inline is not present on script-src.
- [ ] A report-only rollout preceded enforcement, with violations reviewed.
- [ ] A deduplicating report endpoint exists and filters extension noise.
- [ ] Policies differ correctly by environment.
- [ ] No sensitive data is retained in stored violation reports.
- [ ] 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.