feat(disputed): Confirm My Validation button + discussion request modal

Backend: POST /tests/{id}/request-discussion
  - Only callable by the lead whose vote is 'approved' in a disputed test
  - Sends notification to the rejecting lead: 'Lead X confirms their
    approval and wants to discuss your rejection'
  - Logs the action in audit trail

Frontend:
- 'Confirm My Validation' button (amber outline) alongside 'Change to Rejected'
- Opens a modal showing:
    * Explanation: both leads must agree to finalise
    * Other lead's rejection reason/notes
    * What happens next (stays disputed, notification sent, either can change)
- 'Send Discussion Request' → calls the new endpoint → shows success state:
    'Lead username has been notified...'
- Instruction to reach out via team channels to resolve offline

Flow summary for disputed tests:
  Approving lead sees 2 options:
    a) 'Confirm My Validation' → modal → send request → other lead notified
    b) 'Change to Rejected' → validation modal → both agree to reject → rejected

frontend/src/api/tests.ts

@@ -308,6 +308,16 @@ export interface RTImportResult {
   engagement: string;
 }
 
+/** Confirm approval in a disputed test and notify the rejecting lead to discuss. */
+export async function requestDiscussion(testId: string): Promise<{
+  status: string;
+  message: string;
+  rejector_username: string;
+}> {
+  const { data } = await client.post(`/tests/${testId}/request-discussion`);
+  return data;
+}
+
 /** Import results from a real Red Team engagement. */
 export async function importRT(payload: RTImportPayload): Promise<RTImportResult> {
   const { data } = await client.post<RTImportResult>("/tests/import-rt", payload);

frontend/src/components/test-detail/TestDetailHeader.tsx

@@ -1,3 +1,4 @@
+import { useState } from "react";
 import {
   FlaskConical,
   Play,
@@ -10,7 +11,11 @@ import {
   ShieldCheck,
   AlertTriangle,
   MessageSquare,
+  X,
+  UserCheck,
 } from "lucide-react";
+import { useMutation } from "@tanstack/react-query";
+import { requestDiscussion } from "../../api/tests";
 import type { Test, TestState, User } from "../../types/models";
 import LiveTimer from "./LiveTimer";
 
@@ -81,6 +86,13 @@ export default function TestDetailHeader({
 }: TestDetailHeaderProps) {
   const role = user?.role ?? "";
   const currentIdx = STATE_INDEX[test.state];
+  const [showDiscussModal, setShowDiscussModal] = useState(false);
+  const [discussResult, setDiscussResult] = useState<string | null>(null);
+
+  const discussMutation = useMutation({
+    mutationFn: () => requestDiscussion(test.id),
+    onSuccess: (data) => setDiscussResult(data.rejector_username),
+  });
 
   const formatDate = (d: string | null) => {
     if (!d) return null;
@@ -227,14 +239,24 @@ export default function TestDetailHeader({
         const side = role === "red_lead" ? "red" : role === "blue_lead" ? "blue" : null;
         if (side || role === "admin") {
           buttons.push(
-            <button
-              key="change-vote"
-              onClick={() => onOpenValidateModal(side ?? (test.red_validation_status === "approved" ? "red" : "blue"))}
-              className="flex items-center gap-1.5 rounded-lg bg-amber-600 px-4 py-2 text-sm font-medium text-white hover:bg-amber-500 transition-colors"
-            >
-              <XCircle className="h-4 w-4" />
-              Change Vote to Rejected
-            </button>,
+            <div key="disputed-actions" className="flex items-center gap-2">
+              {/* Confirm keeping approval → open discussion modal */}
+              <button
+                onClick={() => { setShowDiscussModal(true); setDiscussResult(null); }}
+                className="flex items-center gap-1.5 rounded-lg border border-amber-500/40 bg-amber-500/10 px-4 py-2 text-sm font-medium text-amber-400 hover:bg-amber-500/20 transition-colors"
+              >
+                <UserCheck className="h-4 w-4" />
+                Confirm My Validation
+              </button>
+              {/* Change vote to rejected */}
+              <button
+                onClick={() => onOpenValidateModal(side ?? (test.red_validation_status === "approved" ? "red" : "blue"))}
+                className="flex items-center gap-1.5 rounded-lg bg-red-700/80 px-4 py-2 text-sm font-medium text-white hover:bg-red-600 transition-colors"
+              >
+                <XCircle className="h-4 w-4" />
+                Change to Rejected
+              </button>
+            </div>,
           );
         }
       }
@@ -458,6 +480,108 @@ export default function TestDetailHeader({
           This test was rejected and needs to be reopened to restart the workflow.
         </div>
       )}
+
+      {/* Confirm My Validation — discussion request modal */}
+      {showDiscussModal && (
+        <div className="fixed inset-0 z-50 flex items-center justify-center bg-black/60 backdrop-blur-sm">
+          <div className="w-full max-w-lg rounded-xl border border-gray-700 bg-gray-900 shadow-2xl">
+            {/* Header */}
+            <div className="flex items-center justify-between border-b border-gray-800 px-6 py-4">
+              <div className="flex items-center gap-2">
+                <UserCheck className="h-5 w-5 text-amber-400" />
+                <h3 className="text-lg font-semibold text-white">Confirm Your Validation</h3>
+              </div>
+              <button onClick={() => { setShowDiscussModal(false); setDiscussResult(null); }}
+                className="rounded p-1 text-gray-400 hover:bg-gray-800 hover:text-white">
+                <X className="h-5 w-5" />
+              </button>
+            </div>
+
+            {!discussResult ? (
+              <div className="px-6 py-5 space-y-4">
+                {/* Conflict summary */}
+                <div className="rounded-lg border border-amber-500/20 bg-amber-500/5 p-4">
+                  <p className="text-sm font-medium text-amber-300 mb-2">
+                    ⚠ Both leads must agree before a test can be finalised
+                  </p>
+                  <p className="text-xs text-gray-400">
+                    You are confirming that your <strong className="text-white">approval is correct</strong> and
+                    that the other lead's rejection should be reviewed.
+                  </p>
+                </div>
+
+                {/* Other lead's rejection reason */}
+                {(test.red_validation_status === "rejected" && test.red_validation_notes) && (
+                  <div>
+                    <p className="mb-1 text-xs font-medium uppercase tracking-wider text-gray-500">Red Lead's rejection reason</p>
+                    <p className="rounded-lg border border-red-500/20 bg-red-900/10 p-3 text-sm italic text-gray-300">
+                      "{test.red_validation_notes}"
+                    </p>
+                  </div>
+                )}
+                {(test.blue_validation_status === "rejected" && test.blue_validation_notes) && (
+                  <div>
+                    <p className="mb-1 text-xs font-medium uppercase tracking-wider text-gray-500">Blue Lead's rejection reason</p>
+                    <p className="rounded-lg border border-red-500/20 bg-red-900/10 p-3 text-sm italic text-gray-300">
+                      "{test.blue_validation_notes}"
+                    </p>
+                  </div>
+                )}
+
+                {/* What happens next */}
+                <div className="rounded-lg border border-gray-700 bg-gray-800/50 p-4 space-y-2">
+                  <p className="text-xs font-semibold text-white">What happens when you send the discussion request:</p>
+                  <ul className="space-y-1 text-xs text-gray-400 list-disc list-inside">
+                    <li>The other lead receives a notification to contact you</li>
+                    <li>The test <strong className="text-white">remains in Disputed</strong> state</li>
+                    <li>Either lead can change their vote at any time to resolve it</li>
+                    <li>If both reject → test becomes Rejected; if both approve → Validated</li>
+                  </ul>
+                </div>
+
+                {discussMutation.isError && (
+                  <p className="text-sm text-red-400">Failed to send notification. Try again.</p>
+                )}
+              </div>
+            ) : (
+              /* Success state */
+              <div className="px-6 py-8 text-center space-y-3">
+                <CheckCircle className="mx-auto h-12 w-12 text-green-400" />
+                <p className="text-lg font-semibold text-white">Discussion request sent</p>
+                <p className="text-sm text-gray-400">
+                  <strong className="text-white">{discussResult}</strong> has been notified
+                  that you are standing by your approval and want to discuss their rejection.
+                </p>
+                <p className="text-xs text-gray-500">
+                  Reach out directly via your team's communication channels to resolve this.
+                </p>
+              </div>
+            )}
+
+            {/* Footer */}
+            <div className="flex justify-end gap-3 border-t border-gray-800 px-6 py-4">
+              <button
+                onClick={() => { setShowDiscussModal(false); setDiscussResult(null); }}
+                className="rounded-lg border border-gray-700 px-4 py-2 text-sm text-gray-400 hover:bg-gray-800"
+              >
+                {discussResult ? "Close" : "Cancel"}
+              </button>
+              {!discussResult && (
+                <button
+                  onClick={() => discussMutation.mutate()}
+                  disabled={discussMutation.isPending}
+                  className="flex items-center gap-2 rounded-lg bg-amber-600 px-4 py-2 text-sm font-medium text-white hover:bg-amber-500 disabled:opacity-50 transition-colors"
+                >
+                  {discussMutation.isPending
+                    ? <><Loader2 className="h-4 w-4 animate-spin" /> Sending…</>
+                    : <><MessageSquare className="h-4 w-4" /> Send Discussion Request</>
+                  }
+                </button>
+              )}
+            </div>
+          </div>
+        </div>
+      )}
     </div>
   );
 }