fix(jira): keep BT Start Date across reopens, resolve Jira accounts on the fly everywhere

- BT Start Date had the same bug RT Start Date did: pushed on every round,
  clobbering round 1's real pickup date. Now only pushed on round 1,
  mirroring the "first round survives every reopen" rule.
- push_test_event's assignment branches (red_executing, red/blue reviewer,
  blue_evaluating reassignment) only read the cached jira_account_id and
  silently no-op'd if it was never populated — which is exactly what
  happened to a blue_lead who hadn't logged in since Jira was configured,
  making it look like Blue's reviewer reassignment was broken when Red's
  wasn't purely because that particular red_lead happened to have logged
  in already. Extracted the live-lookup fallback that only
  push_assignee_update had into a shared _resolve_jira_account_id(), used
  by every assignment call site now.

backend/tests/test_jira_service.py

@@ -391,6 +391,42 @@ def test_push_test_event_red_executing_reassigns_original_operator_on_reopen(moc
     mock_jira.assign_issue.assert_called_once_with(link.jira_issue_key, account_id="red-tech-account")
 
 
+@patch("app.services.jira_service.has_admin_jira_configured", return_value=True)
+@patch("app.services.jira_service.get_admin_jira_client")
+def test_push_test_event_reviewer_assignment_resolves_account_id_on_the_fly(
+    mock_get_client, mock_configured, db,
+):
+    """Regression: a blue_lead assigned as reviewer had never logged in
+    (jira_account_id was still NULL), so the Jira reassignment silently
+    no-op'd and the ticket stayed on the operator forever — while red_lead
+    worked purely by coincidence of already having logged in once. Every
+    assignment call site must attempt a live lookup, not just
+    push_assignee_update."""
+    from app.models.user import User
+
+    mock_jira = MagicMock()
+    mock_jira.user_find_by_user_string.return_value = [
+        {"accountId": "blue-lead-account", "emailAddress": "bluelead@test.com"},
+    ]
+    mock_get_client.return_value = mock_jira
+    test = _make_test()
+    link = _make_link(test.id)
+    db.add(link)
+    db.commit()
+
+    blue_lead = User(
+        username="bluelead-never-logged-in", email="bluelead@test.com",
+        hashed_password="x", role="blue_lead", jira_account_id=None,
+    )
+    db.add(blue_lead)
+    db.commit()
+
+    jira_service.push_test_event(db, test, MagicMock(username="bluetech"), "blue_review", assignee=blue_lead)
+
+    assert blue_lead.jira_account_id == "blue-lead-account"
+    mock_jira.assign_issue.assert_called_once_with(link.jira_issue_key, account_id="blue-lead-account")
+
+
 @patch("app.services.jira_service.has_admin_jira_configured", return_value=True)
 @patch("app.services.jira_service.get_admin_jira_client")
 def test_push_bt_work_started_sets_in_progress(mock_get_client, mock_configured, db):
@@ -412,6 +448,41 @@ def test_push_bt_work_started_sets_in_progress(mock_get_client, mock_configured,
     mock_jira.assign_issue.assert_called_once_with(link.jira_issue_key, account_id="bob-account-id")
 
 
+@patch("app.services.jira_service.has_admin_jira_configured", return_value=True)
+@patch("app.services.jira_service.get_admin_jira_client")
+def test_push_bt_started_sets_date_field_on_round_one(mock_get_client, mock_configured, db):
+    mock_jira = MagicMock()
+    mock_get_client.return_value = mock_jira
+    test = _make_test(blue_round_number=1)
+    link = _make_link(test.id)
+    db.add(link)
+    db.commit()
+
+    jira_service.push_bt_started(db, test)
+
+    mock_jira.update_issue_field.assert_called_once()
+    fields = mock_jira.update_issue_field.call_args[1]["fields"]
+    assert jira_service.JIRA_FIELD_BT_START_DATE in fields
+
+
+@patch("app.services.jira_service.has_admin_jira_configured", return_value=True)
+@patch("app.services.jira_service.get_admin_jira_client")
+def test_push_bt_started_preserves_round_one_date_on_reopen(mock_get_client, mock_configured, db):
+    """Regression: mirrors the RT Start Date bug — BT Start Date must keep
+    showing round 1's real pickup date even after the operator re-claims
+    the test via 'Start Evaluation' on a later round."""
+    mock_jira = MagicMock()
+    mock_get_client.return_value = mock_jira
+    test = _make_test(blue_round_number=2)
+    link = _make_link(test.id)
+    db.add(link)
+    db.commit()
+
+    jira_service.push_bt_started(db, test)
+
+    mock_jira.update_issue_field.assert_not_called()
+
+
 @patch("app.services.jira_service.has_admin_jira_configured", return_value=True)
 @patch("app.services.jira_service.get_admin_jira_client")
 def test_push_rt_submitted_includes_attack_success(mock_get_client, mock_configured, db):