fix(backtest): one window, and stop calling a rejected exit "recommended"

Two ways the recommendation still disagreed with the page it sits on.

It preferred the "all" monitor row while the UI defaulted its selector to "3y",
so a default page load showed one set of returns in the tiles and a different
set in the recommendation. The row it used is now published as basis_lookback
and the page defaults to it, so the two cannot open on different windows. The
test fixture gains a second monitor row with different numbers — with only an
"all" row present, a lookback mix-up could not fail.

Robustness picked its basis between "the recommended Nd hold" and "the S/R
target exit", naming an exit the production book replaced as recommended. There
is no ATR-trail ex-top-5% figure in the report, so it now always reports the
gate-level grading and says that is what it is, rather than dressing a legacy
number as a verdict on the production book. time_exit_sweep is no longer read
here at all.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

tests/unit/test_backtest_service.py

@@ -1287,6 +1287,12 @@ def test_build_recommendation_reads_the_report():
                 "strategy": "prod", "lookback": "all", "lookback_label": "All history",
                 "cagr_pct": 40.0, "sharpe": 1.72, "max_drawdown_pct": 17.7,
                 "total_return_pct": 297.8, "spy_return_pct": 101.9,
+            }, {
+                # A second window with DIFFERENT numbers. Without it the "all"
+                # preference is untested and a lookback mix-up cannot fail.
+                "strategy": "prod", "lookback": "3y", "lookback_label": "3y",
+                "cagr_pct": 47.9, "sharpe": 1.96, "max_drawdown_pct": 17.3,
+                "total_return_pct": 220.9, "spy_return_pct": 71.5,
             }],
         },
     }
@@ -1308,12 +1314,21 @@ def test_build_recommendation_reads_the_report():
     assert "keep the NEUTRAL exclusion" in gate_texts
     assert "80" in by_topic["cutoff"][0]
     assert "beats" in by_topic["benchmark"][0]
-    # robustness is judged under the RECOMMENDED exit (the 30d hold), not the
-    # target model the recommendation advises abandoning
-    assert any(
-        "not a handful of outliers" in t and "under the recommended 30d hold" in t
-        for t in by_topic["robustness"]
-    )
+
+    # Every production figure comes from ONE window, and the report says which,
+    # so the page can default its selector to the same one.
+    assert rec["basis_lookback"] == "all"
+    assert rec["basis_lookback_label"] == "All history"
+    assert "+40.0%" in by_topic["production"][0]
+    assert "47.9" not in by_topic["production"][0]   # the 3y row must not leak in
+    assert "220.9" not in by_topic["benchmark"][0]
+
+    # Robustness names its real basis. It used to claim "under the recommended
+    # 30d hold" — nothing recommends that exit; production is the ATR trail.
+    robustness = by_topic["robustness"][0]
+    assert "not a handful of outliers" in robustness
+    assert "gate-level grading" in robustness
+    assert "recommended" not in robustness
 
 
 def test_build_recommendation_flags_outlier_dependence():