Add Phase Z classifier placement diagnostics

- consume debug_zones[i].placement_trace in classify_visual_runtime_check
- surface per-zone diagnostic in fit_classification.placement_diagnostics
- preserve canonical render SHA and existing classifier output schema

src/phase_z2_classifier.py

@@ -288,6 +288,51 @@ def classify_overflow(
 # ─── visual_runtime_check 결과 → 전체 fit_classification trace ────
 
 
+def _build_placement_diagnostic_for_zone(
+    zone_position: str,
+    placement_trace: Optional[dict],
+    mapper_template_id: Optional[str],
+) -> dict:
+    """zone 별 placement diagnostic 빌더 — placement_trace from B4 → 진단 dict.
+
+    phase_z2_pipeline.py 의 trace-only B1→B2→B4 chain 결과 (debug_zones[i].placement_trace)
+    를 per-zone surface 한 진단. classifier 는 *consume only* — placement_trace
+    raw 구조는 미변경.
+
+    Args:
+        zone_position      : zone position ("top" / "bottom_l" 등)
+        placement_trace    : phase_z2_pipeline.py 의 placement_trace dict 또는 None
+        mapper_template_id : 기존 mapper / V4 가 선택한 frame template_id
+                             (placement_trace 에 mapper_frame_template_id 누락 시 fallback)
+
+    Returns:
+        per-zone placement diagnostic dict (shape-stable, missing fields = None / 0).
+    """
+    if placement_trace is None:
+        return {
+            "zone_position": zone_position,
+            "mapper_frame_template_id": mapper_template_id,
+            "b4_selected_template_id": None,
+            "frame_selection_matches_mapper": None,
+            "frame_selection_match_note": "no placement_trace recorded",
+            "region_count": 0,
+            "slot_assignment_count": 0,
+            "rejection_count": 0,
+        }
+    return {
+        "zone_position": zone_position,
+        "mapper_frame_template_id": (
+            placement_trace.get("mapper_frame_template_id") or mapper_template_id
+        ),
+        "b4_selected_template_id": placement_trace.get("selected_template_id"),
+        "frame_selection_matches_mapper": placement_trace.get("frame_selection_matches_mapper"),
+        "frame_selection_match_note": placement_trace.get("frame_selection_match_note"),
+        "region_count": len(placement_trace.get("internal_regions") or []),
+        "slot_assignment_count": len(placement_trace.get("slot_assignments") or []),
+        "rejection_count": len(placement_trace.get("rejection") or []),
+    }
+
+
 def classify_visual_runtime_check(overflow: dict, debug_zones: list[dict]) -> dict:
     """Selenium overflow + composition 의 zone debug → 전체 fit_classification 산출.
 
@@ -304,7 +349,21 @@ def classify_visual_runtime_check(overflow: dict, debug_zones: list[dict]) -> di
           summary                 : 텍스트 요약 (n events, categories seen)
           categories_seen         : 등장한 카테고리 unique list
           unclassified_signals    : 미분류 신호 (raw Selenium 결과 중 분류 안 된 것)
+          placement_diagnostics   : per-zone placement_trace 진단 (B4 vs mapper
+                                    divergence + region / slot_assignment / rejection
+                                    count) — passed 여부 무관 항상 surface
     """
+    # placement_diagnostics — debug_zones[i].placement_trace 를 per-zone diagnostic 으로 surface.
+    # passed 여부 무관 항상 빌드 (B4 vs mapper divergence 가 passed 에서도 진단 가치).
+    placement_diagnostics = [
+        _build_placement_diagnostic_for_zone(
+            zone_position=dz.get("position", "?"),
+            placement_trace=dz.get("placement_trace"),
+            mapper_template_id=dz.get("v4_template_id"),
+        )
+        for dz in (debug_zones or [])
+    ]
+
     if overflow.get("passed", False):
         return {
             "visual_check_passed": True,
@@ -312,6 +371,7 @@ def classify_visual_runtime_check(overflow: dict, debug_zones: list[dict]) -> di
             "summary": "visual check passed — no overflow to classify",
             "categories_seen": [],
             "unclassified_signals": [],
+            "placement_diagnostics": placement_diagnostics,
         }
 
     # zone position → debug_zones 매핑 (capacity_fit_status 추출용)
@@ -392,4 +452,5 @@ def classify_visual_runtime_check(overflow: dict, debug_zones: list[dict]) -> di
         ),
         "categories_seen": categories,
         "unclassified_signals": unclassified,
+        "placement_diagnostics": placement_diagnostics,
     }