diff --git a/pilot/opencode_review.py b/pilot/opencode_review.py
index f9ffc49..c2524ab 100644
--- a/pilot/opencode_review.py
+++ b/pilot/opencode_review.py
@@ -55,7 +55,7 @@ import time
 import urllib.error
 import urllib.request
 
-from ai_review import is_test_path
+from ai_review import _SEVERITY_EMOJI, is_test_path
 
 # Where the factory lives (opencode.json + .opencode/). Default: the pragent
 # repo root (this file is at <root>/pilot/opencode_review.py).
@@ -567,14 +567,6 @@ _LENS_ID_RE = re.compile(r"^[a-z0-9-]{1,32}$")
 SEVERITY_ORDER = ("low", "medium", "high", "critical")
 SEVERITY_RANK = {s: i for i, s in enumerate(SEVERITY_ORDER)}
 
-# Local emoji map for the synthesized walkthrough. Kept separate from
-# `ai_review._SEVERITY_EMOJI` (which also has "trivial"/"info"/"nit") so
-# this stays a small surface for the fallback path.
-_SEVERITY_EMOJI_SUMMARY = {
-    "critical": "🔴", "high": "🔴", "medium": "🟡",
-    "low": "🔵", "trivial": "⚪", "info": "⚪",
-}
-
 
 @_dc.dataclass(frozen=True)
 class ReviewerSpec:
@@ -941,6 +933,10 @@ def _synthesize_summary_fields(
         `is_test_path`, else "No tests for behavioral change in `<path>`."
         pointing at the first non-test path.
     """
+    # None-safe: callers occasionally pass None when the upstream merger
+    # short-circuited. Treat as empty so the for-loop and group-by below
+    # never crash.
+    findings = findings or []
     # walkthrough
     walkthrough: list[str] = []
     if findings:
@@ -954,8 +950,7 @@ def _synthesize_summary_fields(
             )
             problem_lines = (peak.get("problem") or "").splitlines()
             problem = problem_lines[0][:80].strip() if problem_lines else ""
-            emoji = _SEVERITY_EMOJI_SUMMARY.get(
-                peak.get("severity", "low"), "⚪")
+            emoji = _SEVERITY_EMOJI.get(peak.get("severity", "low"), "⚪")
             walkthrough.append(f"`{path}` — {emoji} {problem}")
     else:
         files = changed_paths if changed_paths is not None else changed_files(diff)
diff --git a/tests/pilot/test_opencode_review.py b/tests/pilot/test_opencode_review.py
index 2e833b0..1d4f4f0 100644
--- a/tests/pilot/test_opencode_review.py
+++ b/tests/pilot/test_opencode_review.py
@@ -905,3 +905,47 @@ 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
+
+
+def test_synthesize_walkthrough_picks_peak_severity_per_path():
+    # Three findings on the same path, with mixed severities. The walkthrough
+    # headline should use the PEAK severity's emoji (critical = 🔴), not the
+    # lexicographic-first severity (low).
+    findings = [
+        {"path": "x.py", "line": 1, "severity": "low",
+         "problem": "minor nit"},
+        {"path": "x.py", "line": 5, "severity": "critical",
+         "problem": "sql injection"},
+        {"path": "x.py", "line": 9, "severity": "high",
+         "problem": "auth bypass"},
+    ]
+    w, _, _ = oc._synthesize_summary_fields(findings, "")
+    assert len(w) == 1
+    line = w[0]
+    assert "`x.py`" in line
+    assert "🔴" in line        # critical = 🔴
+    assert "🟡" not in line
+    assert "🔵" not in line
+    assert "sql injection" in line  # critical finding's problem, not low's
+
+
+def test_synthesize_summary_fields_none_findings_safe():
+    # Old code crashed in risk_verdict with `for f in findings:` on None.
+    # After the `findings = findings or []` guard, None behaves like [].
+    w, rv, tc = oc._synthesize_summary_fields(None, "")
+    assert isinstance(w, list)
+    assert rv.startswith("Low risk")
+    # walkthrough should fall through to the diff-derived path list — empty
+    # diff produces no lines, but no crash is the point.
+    assert tc == ""
+
+
+def test_synthesize_walkthrough_empty_problem_does_not_crash():
+    # An empty `problem` should render as "`a.py` — emoji" with a trailing
+    # space, not raise. Regression guard for splitlines()[0][:80].strip().
+    findings = [{"path": "a.py", "line": 1,
+                 "severity": "low", "problem": ""}]
+    w, _, _ = oc._synthesize_summary_fields(findings, "")
+    assert len(w) == 1
+    assert "`a.py`" in w[0]
+    assert "🔵" in w[0]  # low severity emoji