Add 'Resolve with Duo' button to MR conflict widget

Summary

Adds a "Resolve with Duo" button to the merge request conflict resolution page and the MR widget merge checks. When clicked, it triggers the developer/v1 foundational flow with a simple goal: resolve the conflicts, push, and post a summary comment.

Implementation

EE component (ee/app/assets/javascripts/merge_conflicts/components/resolve_with_duo_button.vue):

• Wraps the existing DuoWorkflowAction widget which handles all enablement/license checks
• Builds a simple goal string with the MR path and IID
• Checks mr_ai_resolve_conflicts feature flag via glFeatures mixin
• Uses ee_component pattern (no CE stub needed)

Backend (ee/app/helpers/ee/merge_requests_helper.rb, ee/app/controllers/ee/projects/merge_requests/conflicts_controller.rb):

• can_resolve_with_ai? checks: MR has conflicts, user can push
• EE conflicts controller pushes the feature flag to the frontend

Conflicts page integration (ee/app/views/projects/merge_requests/conflicts/_resolve_with_ai.html.haml):

• Renders Vue mount point with MR data attributes when can_resolve_with_ai? is true
• initResolveWithDuo() mounts the button with Apollo provider

MR widget (app/assets/javascripts/vue_merge_request_widget/components/checks/conflicts.vue):

• Dynamically imports EE button via ee_component pattern
• Shows button alongside conflict action buttons when check is failed

DuoWorkflowAction (ee/app/assets/javascripts/ai/shared/widgets/duo_workflow_action.vue):

• Added category prop passthrough (was hardcoded to primary)

Feature flag: mr_ai_resolve_conflicts (wip, disabled by default)

• Pushed to frontend in EE conflicts controller and EE MR controller
• Checked client-side in Vue component via glFeatures

How it works

Uses the existing Duo Developer flow (developer/v1) with a concise goal:

1. Resolve the merge conflicts in merge request <project>!<iid>
2. Directly commit and push to the MR
3. Post a summary comment listing what was resolved

The agent determines the right approach autonomously — no tool names or step-by-step instructions are included in the goal (per reviewer feedback).

Related

• Epic: gitlab-org#20688
• Phase 3: #588530 (closed)
• Rollout issue: #596465

Test plan

• Enable feature flag: Feature.enable(:mr_ai_resolve_conflicts)
• Create MR with merge conflicts
• Navigate to conflict resolution page (Resolve conflicts button)
• Verify "Resolve with Duo" button appears
• Click button → Duo workflow session starts
• Verify agent resolves conflicts and pushes to source branch
• Verify button hidden when: feature flag off, no conflicts, user lacks permission, Duo disabled
• Verify button also appears in MR widget merge checks (conflict check row)