feat(TASK-018): review-gauntlet lane degradation + verification passthrough

- lane_fault.py + fallback on all four run_* lane nodes: an agent-node
  failure is normalized into a PIPELINE-FAULT lane result instead of
  killing the graph
- verdict_gate.py: PIPELINE-FAULT lane results block distinctly from
  SKIPPED and missing-sentinel; a PIPELINE-FAULT in signals_error blocks
  at the gauntlet level
- build_items.py: restructured into main() + fail-closed guard (crash
  emits empty lanes + PIPELINE-FAULT) and folds lanes_degraded into
  lanes_summary
- parse: state_updates/fallback -> parse_fault.py, which records the
  fault in signals_error and jumps to the verdict gate
- select_lanes: state_updates/fallback -> default_lanes.py, a
  deterministic wider-never-narrower lane fallback
- verification_commands threaded through parse into run_adversary's
  prompt (declared-only, never invented)
- run_probe prompt gains the aborted-attempt reconcile line
- 8 gauntlet_* R5 tests in src/config/request_context.rs (script harness
  + graph interpolation)

assets/agents/review-gauntlet/scripts/verdict_gate.py

@@ -5,6 +5,9 @@ Parses each configured lane's verdict SENTINEL with a regex — no LLM
 re-reads, no judgment. The gate's hard rules:
 
   - a missing sentinel is a LANE FAILURE and blocks — never a pass;
+  - a PIPELINE-FAULT lane result (the lane's agent died after retries) or a
+    PIPELINE-FAULT in signals_error (builder/parse fault) blocks — a
+    degraded pipeline is never a pass;
   - any 🔴 finding in the code-review report blocks regardless of the
     lane's own verdict line;
   - NEEDS-HUMAN without 🔴 passes but is surfaced as attention required;
@@ -40,10 +43,26 @@ def main():
     def record(lane, status, detail=""):
         lane_lines.append(f"| {lane} | {status} | {detail} |")
 
+    def fault_excerpt(report):
+        line = next(
+            (ln for ln in report.splitlines() if "PIPELINE-FAULT:" in ln), report
+        )
+        return line.strip()[:200]
+
+    def lane_fault_blocker(lane, report):
+        blockers.append(
+            f"{lane}: PIPELINE-FAULT — the lane failed after retries and produced "
+            f"no verdict; a degraded lane is never a pass ({fault_excerpt(report)})"
+        )
+        record(lane, "BLOCKED", "PIPELINE-FAULT (lane failed)")
+
     # --- code-review ------------------------------------------------------
     cr = lane_report("code_review_results")
     if cr is None:
         record("code-review", "SKIPPED", "not selected")
+    elif "PIPELINE-FAULT:" in cr:
+        lane_fault_blocker("code-review", cr)
+        reports.append(("code-review", cr))
     else:
         reports.append(("code-review", cr))
         m = re.search(r"Verdict:\**\s*\**\s*(MERGE-READY|NEEDS-HUMAN)", cr)
@@ -72,6 +91,9 @@ def main():
     adv = lane_report("adversary_results")
     if adv is None:
         record("adversary", "SKIPPED", "not selected")
+    elif "PIPELINE-FAULT:" in adv:
+        lane_fault_blocker("adversary", adv)
+        reports.append(("adversary", adv))
     else:
         reports.append(("adversary", adv))
         m = re.search(r"ADVERSARIAL_REVIEW:\s*(CONFORMS|DIVERGES)", adv)
@@ -92,6 +114,9 @@ def main():
     sec = lane_report("security_results")
     if sec is None:
         record("security", "SKIPPED", "not selected")
+    elif "PIPELINE-FAULT:" in sec:
+        lane_fault_blocker("security", sec)
+        reports.append(("security", sec))
     else:
         reports.append(("security", sec))
         m = re.search(r"SECURITY_REVIEW:\s*(PASS|FAIL)", sec)
@@ -110,6 +135,9 @@ def main():
     pb = lane_report("probe_results")
     if pb is None:
         record("probe", "SKIPPED", "not selected")
+    elif "PIPELINE-FAULT:" in pb:
+        lane_fault_blocker("probe", pb)
+        reports.append(("probe", pb))
     else:
         reports.append(("probe", pb))
         m = re.search(r"USAGE_PROBE:\s*(PASS|FAIL|INCONCLUSIVE)", pb)
@@ -131,6 +159,12 @@ def main():
             )
             record("probe", "BLOCKED", "missing verdict sentinel")
 
+    # A gauntlet-level fault (build_items crash, dead parse stage) means the
+    # lanes above were never built — SKIPPED rows alone must not read as PASS.
+    signals_error = state.get("signals_error")
+    if isinstance(signals_error, str) and "PIPELINE-FAULT:" in signals_error:
+        blockers.append(f"pipeline: {signals_error}")
+
     verdict = "BLOCKED" if blockers else "PASS"
 
     md = "\n".join(