Add MODE=pcb layout exam job with AI and deterministic checks.

Parallel pcb_status pipeline: parse board, classify domains/groups,
inventory traces, PE-LAY/PLC/SI/DRT checks, per-IC datasheet review.
Findings merge into the report UI. No auto-place or pcbnew write-back.

backend/services/validation.py

@@ -26,7 +26,6 @@ from backend.periscopex.models import (
     ComponentType,
     DesignGraph,
     Finding,
-    LayoutGraph,
     NetType,
     ValidationReport,
 )
@@ -61,8 +60,6 @@ from backend.periscopex.dnp_check import check_dnp_enables
 from backend.periscopex.lifecycle import check_lifecycle, load_lifecycle_dir
 from backend.periscopex.errata_check import check_errata
 from backend.periscopex.internal_features_check import check_internal_features
-from backend.periscopex.placement_check import check_placement
-from backend.periscopex.si_check import check_si
 from backend.periscopex.crystal_cl_check import check_crystal_cl
 from backend.periscopex.nc_pin_check import check_nc_pins
 
@@ -77,7 +74,6 @@ def _is_deterministic(f: Finding) -> bool:
 def _run_deterministic_checks(
     graph: DesignGraph, constraints_map: dict,
     lifecycle_map: dict | None = None,
-    layout: LayoutGraph | None = None,
 ) -> list[Finding]:
     """Run the deterministic graph checks, fail-soft per check — a check bug
     can never break the review or the report."""
@@ -100,8 +96,6 @@ def _run_deterministic_checks(
         ("lifecycle_check", lambda: check_lifecycle(graph, lifecycle_map)),
         ("errata_check", lambda: check_errata(graph, constraints_map)),
         ("internal_features_check", lambda: check_internal_features(graph, constraints_map)),
-        ("placement_check", lambda: check_placement(graph, constraints_map, layout)),
-        ("si_check", lambda: check_si(graph, constraints_map, layout)),
         ("crystal_cl_check", lambda: check_crystal_cl(graph)),
         ("nc_pin_check", lambda: check_nc_pins(graph, constraints_map)),
     ):
@@ -112,17 +106,6 @@ def _run_deterministic_checks(
     return out
 
 
-def _load_layout_graph(graph_path: str) -> LayoutGraph | None:
-    path = Path(graph_path).with_name("layout_graph.json")
-    if not path.is_file():
-        return None
-    try:
-        return LayoutGraph.model_validate_json(path.read_text())
-    except Exception:
-        log.exception("layout_graph.json invalid — skipping placement_check")
-        return None
-
-
 def _assistant_text(blocks) -> str:
     """Best-effort extraction of text content from a completion's raw
     assistant blocks. Provider-agnostic and never raises."""
@@ -312,6 +295,9 @@ async def review_ic_async(
     pdf_dir: Path | None = None,
     storage=None,
     excerpt_cache: dict | None = None,
+    extra_context: str = "",
+    system_prompt: str | None = None,
+    log_stage: str = "review",
 ) -> tuple[ReviewResult, dict]:
     """Review one IC against its datasheet. Async, multi-turn.
 
@@ -373,7 +359,7 @@ async def review_ic_async(
 
             session = await provider.create_session(
                 model=model,
-                system=SYSTEM_PROMPT,
+                system=system_prompt or SYSTEM_PROMPT,
                 # Gemini 2.5/3 thinking models count thoughts against this cap.
                 # 4096 was too tight: U3 (largest IC) burned the entire budget
                 # on thinking and emitted zero visible output, dropping its
@@ -387,13 +373,16 @@ async def review_ic_async(
             )
             try:
                 context = build_component_context(graph, constraints_map, ic_ref)
+                user_text = f"Review this component's usage:\n\n{context}"
+                if extra_context.strip():
+                    user_text += "\n\n" + extra_context.strip()
 
                 initial_msg = Message(
                     role="user",
                     content=[
                         PdfBlock(path=Path(trimmed_pdf), cacheable=True),
                         TextBlock(
-                            text=f"Review this component's usage:\n\n{context}",
+                            text=user_text,
                             cacheable=True,
                         ),
                     ],
@@ -503,7 +492,7 @@ async def review_ic_async(
                                 )
                             if api_logger:
                                 api_logger.log(
-                                    stage="review", identifier=ic_ref,
+                                    stage=log_stage, identifier=ic_ref,
                                     model=model, provider=provider.name,
                                     input_tokens=total_input, output_tokens=total_output,
                                     cache_creation_input_tokens=total_cache_creation,
@@ -607,7 +596,7 @@ async def review_ic_async(
                 trace["duration_ms"] = int((time.monotonic() - t0) * 1000)
                 if api_logger:
                     api_logger.log(
-                        stage="review", identifier=ic_ref,
+                        stage=log_stage, identifier=ic_ref,
                         model=model, provider=provider.name,
                         input_tokens=total_input, output_tokens=total_output,
                         cache_creation_input_tokens=total_cache_creation,
@@ -730,7 +719,7 @@ async def validate_design_async(
         if loaded:
             lifecycle_map.update(loaded)
     deterministic_findings = _run_deterministic_checks(
-        graph, constraints_map, lifecycle_map, layout=_load_layout_graph(graph_path),
+        graph, constraints_map, lifecycle_map,
     )
 
     pdf_dir_path = Path(pdf_dir)