feat(opencode_review): python fallback for summary fields

tests/pilot/test_opencode_review.py

@@ -859,3 +859,49 @@ def test_no_surface_response_zero_lenses_wording():
     summary, findings, _c, _r, _w, _rv, _tc = ai_review.parse_review_output(text)
     assert findings == []
     assert "after path filtering" in summary
+
+
+# ---------------------------------------------------------------------------
+# _synthesize_summary_fields — Task 8: real Python fallback implementation
+# ---------------------------------------------------------------------------
+
+
+def test_synthesize_walkthrough_groups_findings_by_path():
+    findings = [
+        {"path": "a.py", "line": 1, "severity": "medium", "problem": "fix x"},
+        {"path": "b.py", "line": 2, "severity": "high", "problem": "fix y"},
+    ]
+    w, _, _ = oc._synthesize_summary_fields(findings, "")
+    assert any("a.py" in line for line in w)
+    assert any("b.py" in line for line in w)
+
+
+def test_synthesize_walkthrough_empty_when_no_findings_uses_changed_files():
+    w, _, _ = oc._synthesize_summary_fields(
+        [],
+        "diff --git a/x.py b/x.py\n@@ -1 +1 @@\n-old\n+new\n+++ b/x.py\n",
+    )
+    assert any("x.py" in line for line in w)
+
+
+def test_synthesize_risk_verdict_critical():
+    findings = [{"severity": "critical"}]
+    _, rv, _ = oc._synthesize_summary_fields(findings, "")
+    assert "Critical risk" in rv
+
+
+def test_synthesize_risk_verdict_clean():
+    _, rv, _ = oc._synthesize_summary_fields([], "")
+    assert "Low risk" in rv
+
+
+def test_synthesize_test_coverage_with_test_path():
+    _, _, tc = oc._synthesize_summary_fields(
+        [], "+diff\n", changed_paths=["pilot/foo.py", "tests/test_foo.py"])
+    assert tc == "Tests changed"
+
+
+def test_synthesize_test_coverage_missing_tests():
+    _, _, tc = oc._synthesize_summary_fields(
+        [], "+diff\n", changed_paths=["pilot/foo.py"])
+    assert "No tests for behavioral change" in tc