SAST False Positive Detection – Frontend – Expose toggle to Security Managers
# TL;DR
Extend the `visibleSettings` allowlist to show the SAST False Positive Detection toggle to Security Managers on the project settings page.
## Acceptance Criteria
- [ ] Security Manager sees the SAST FP toggle on the GitLab Duo settings section
- [ ] Security Manager sees only permitted toggles (SAST VR + FP); other Duo settings remain hidden
- [ ] `DUO_SAST_FP_DETECTION_ENABLED` constant is added to frontend constants
- [ ] `gitlab_duo_visible_settings` helper returns FP identifier for Security Managers
- [ ] Frontend specs and feature spec are added
## Implementation Details
**Files to modify:**
| File | Change |
|------|--------|
| `app/assets/javascripts/pages/projects/shared/permissions/constants.js` | Add `export const DUO_SAST_FP_DETECTION_ENABLED = 'duoSastFpDetectionEnabled';` |
| `app/assets/javascripts/pages/projects/shared/permissions/components/gitlab_duo_settings.vue` | Import new constant; add `v-if="isSettingVisible($options.DUO_SAST_FP_DETECTION_ENABLED)"` guard to the SAST FP toggle row |
| `ee/app/helpers/ee/projects_helper.rb` | Extend `gitlab_duo_visible_settings` to include `'duoSastFpDetectionEnabled'` for Security Managers |
| `ee/spec/helpers/projects_helper_spec.rb` | Test `visibleSettings` includes `duoSastFpDetectionEnabled` |
| `spec/frontend/pages/projects/shared/permissions/components/gitlab_duo_settings_spec.js` | Add specs for FP toggle visibility |
| `ee/spec/features/projects/settings/security_manager_manages_fp_setting_spec.rb` | Create feature spec (mirror `security_manager_manages_sast_vr_setting_spec.rb`) |
**Reference implementation:** See !239266 for the exact pattern used for SAST VR (`DUO_SAST_VR_WORKFLOW_ENABLED`).
## Testing Approach
- [ ] Unit tests for helper and Vue component
- [ ] Feature spec for end-to-end validation
- [ ] Manual validation steps:
1. Start GDK with `GITLAB_SECURITY_MANAGER_ROLE=true`
2. Enable feature flags: `update_sast_vr_setting_permission`
3. Login as Security Manager
4. Navigate to project Settings → General → GitLab Duo
5. Verify only SAST VR and SAST FP toggles are visible
6. Verify the FP toggle can be toggled and saved
## Estimate
issue