diff --git a/src/app/(dashboard)/dashboard/compression/studio/PlayView.tsx b/src/app/(dashboard)/dashboard/compression/studio/PlayView.tsx
index fd5b102fba..d7bc933217 100644
--- a/src/app/(dashboard)/dashboard/compression/studio/PlayView.tsx
+++ b/src/app/(dashboard)/dashboard/compression/studio/PlayView.tsx
@@ -7,6 +7,8 @@ import { PlaygroundInput, LANE_ENGINES } from "./PlaygroundInput";
 export interface PlayViewProps { text: string; onText: (t: string) => void; laneEngines?: readonly string[]; }
 
 function laneStatus(l: Lane): string {
+  const rejected = l.run?.steps?.find((s) => s.rejected);
+  if (rejected) return `⚠ rejeitado: ${rejected.rejectReason ?? ""}`;
   return l.error ? "⚠ erro" : l.run ? `−${l.run.savingsPercent}%` : "—";
 }
 
@@ -31,15 +33,16 @@ function LaneList({ lanes, onSelect }: { lanes: Lane[]; onSelect: (e: string) =>
 export function PlayView({ text, onText, laneEngines = LANE_ENGINES }: PlayViewProps) {
   const [active, setActive] = useState<string[]>(["rtk", "caveman"]);
   const [selectedLane, setSelectedLane] = useState<string | null>(null);
+  const [fidelityGate, setFidelityGate] = useState(false);
   const { batch, loading, run } = usePreviewCompression();
   const messages = [{ role: "user", content: text }];
   const toggle = (e: string) => setActive((a) => (a.includes(e) ? a.filter((x) => x !== e) : [...a, e]));
-  const onRun = () => run({ messages, laneEngines: [...laneEngines], activeEngines: orderByStack(active, laneEngines) });
+  const onRun = () => run({ messages, laneEngines: [...laneEngines], activeEngines: orderByStack(active, laneEngines), fidelityGate });
   const activeDiff = resolveActiveDiff(batch, selectedLane);
   return (
     <div className="flex h-full gap-3">
       <div className="w-[260px] shrink-0">
-        <PlaygroundInput text={text} onText={onText} active={active} onToggleActive={toggle} onRun={onRun} loading={loading} />
+        <PlaygroundInput text={text} onText={onText} active={active} onToggleActive={toggle} onRun={onRun} loading={loading} fidelityGate={fidelityGate} onToggleFidelity={() => setFidelityGate((v) => !v)} />
       </div>
       <div className="flex min-w-0 flex-1 flex-col gap-3 overflow-auto">
         {batch?.combined && (
diff --git a/src/app/(dashboard)/dashboard/compression/studio/PlaygroundInput.tsx b/src/app/(dashboard)/dashboard/compression/studio/PlaygroundInput.tsx
index d960c1e41b..21cd107173 100644
--- a/src/app/(dashboard)/dashboard/compression/studio/PlaygroundInput.tsx
+++ b/src/app/(dashboard)/dashboard/compression/studio/PlaygroundInput.tsx
@@ -1,7 +1,7 @@
 "use client";
 export const LANE_ENGINES = ["session-dedup", "ccr", "lite", "rtk", "headroom", "caveman", "aggressive", "ultra"] as const;
-export interface PlaygroundInputProps { text: string; onText: (t: string) => void; active: string[]; onToggleActive: (engine: string) => void; onRun: () => void; loading: boolean; }
-export function PlaygroundInput({ text, onText, active, onToggleActive, onRun, loading }: PlaygroundInputProps) {
+export interface PlaygroundInputProps { text: string; onText: (t: string) => void; active: string[]; onToggleActive: (engine: string) => void; onRun: () => void; loading: boolean; fidelityGate: boolean; onToggleFidelity: () => void; }
+export function PlaygroundInput({ text, onText, active, onToggleActive, onRun, loading, fidelityGate, onToggleFidelity }: PlaygroundInputProps) {
   return (
     <div className="flex flex-col gap-3">
       <textarea data-testid="play-input" className="min-h-[160px] w-full rounded border p-2 font-mono text-xs" value={text} onChange={(e) => onText(e.target.value)} placeholder="Cole prompt / tool-output / contexto..." />
@@ -10,6 +10,10 @@ export function PlaygroundInput({ text, onText, active, onToggleActive, onRun, l
         {LANE_ENGINES.map((e) => (<label key={e} className="flex items-center gap-2 text-sm"><input type="checkbox" checked={active.includes(e)} onChange={() => onToggleActive(e)} />{e}</label>))}
         <label className="flex items-center gap-2 text-sm opacity-50"><input type="checkbox" disabled /> llmlingua <span className="text-[10px]">(requer modelo ONNX)</span></label>
       </div>
+      <label className="flex items-center gap-2 text-sm">
+        <input type="checkbox" data-testid="fidelity-toggle" checked={fidelityGate} onChange={onToggleFidelity} />
+        Verificar fidelidade (rejeitar camada que corromper)
+      </label>
       <button data-testid="play-run" className="rounded bg-blue-500/30 py-2 font-semibold" onClick={onRun} disabled={loading}>{loading ? "Rodando..." : "▶ Run"}</button>
     </div>
   );
diff --git a/src/app/(dashboard)/dashboard/compression/studio/compressionFlowModel.ts b/src/app/(dashboard)/dashboard/compression/studio/compressionFlowModel.ts
index 91b93d0764..1f87b50667 100644
--- a/src/app/(dashboard)/dashboard/compression/studio/compressionFlowModel.ts
+++ b/src/app/(dashboard)/dashboard/compression/studio/compressionFlowModel.ts
@@ -21,6 +21,8 @@ export interface CompressionEngineStep {
   techniquesUsed: string[];
   rulesApplied?: string[];
   durationMs?: number;
+  rejected?: boolean;
+  rejectReason?: string;
 }
 
 // ── Diff ─────────────────────────────────────────────────────────────────
diff --git a/src/hooks/usePreviewCompression.ts b/src/hooks/usePreviewCompression.ts
index 36e6eda076..d5c9533a7d 100644
--- a/src/hooks/usePreviewCompression.ts
+++ b/src/hooks/usePreviewCompression.ts
@@ -4,7 +4,7 @@ import { previewToRunModel, type CompressionRunModel, type PreviewResponse } fro
 export interface PreviewMessage { role: string; content: unknown; }
 export interface Lane { engine: string; run: CompressionRunModel | null; error: string | null; }
 export interface PreviewBatch { lanes: Lane[]; combined: CompressionRunModel | null; diff: PreviewResponse["diff"] | null; }
-export interface RunPreviewArgs { messages: PreviewMessage[]; laneEngines: string[]; activeEngines: string[]; language?: string; }
+export interface RunPreviewArgs { messages: PreviewMessage[]; laneEngines: string[]; activeEngines: string[]; language?: string; fidelityGate?: boolean; }
 async function postPreview(payload: Record<string, unknown>): Promise<PreviewResponse> {
   const res = await fetch("/api/compression/preview", { method: "POST", headers: { "Content-Type": "application/json" }, body: JSON.stringify(payload) });
   const data = await res.json();
@@ -12,17 +12,17 @@ async function postPreview(payload: Record<string, unknown>): Promise<PreviewRes
   return data as PreviewResponse;
 }
 export async function runPreviewBatch(args: RunPreviewArgs): Promise<PreviewBatch> {
-  const { messages, laneEngines, activeEngines } = args;
+  const { messages, laneEngines, activeEngines, fidelityGate } = args;
   const lanes: Lane[] = await Promise.all(
     laneEngines.map(async (engine): Promise<Lane> => {
-      try { const res = await postPreview({ messages, engineId: engine }); return { engine, run: previewToRunModel(res, engine), error: null }; }
+      try { const res = await postPreview({ messages, engineId: engine, ...(fidelityGate ? { fidelityGate: { enabled: true } } : {}) }); return { engine, run: previewToRunModel(res, engine), error: null }; }
       catch (e) { return { engine, run: null, error: e instanceof Error ? e.message : "error" }; }
     })
   );
   let combined: CompressionRunModel | null = null;
   let diff: PreviewResponse["diff"] | null = null;
   if (activeEngines.length > 0) {
-    try { const res = await postPreview({ messages, pipeline: activeEngines }); combined = previewToRunModel(res, activeEngines.join(" → ")); diff = res.diff; }
+    try { const res = await postPreview({ messages, pipeline: activeEngines, ...(fidelityGate ? { fidelityGate: { enabled: true } } : {}) }); combined = previewToRunModel(res, activeEngines.join(" → ")); diff = res.diff; }
     catch { combined = null; }
   }
   return { lanes, combined, diff };
diff --git a/tests/unit/ui/fidelityGateToggle.test.tsx b/tests/unit/ui/fidelityGateToggle.test.tsx
new file mode 100644
index 0000000000..f55756f8aa
--- /dev/null
+++ b/tests/unit/ui/fidelityGateToggle.test.tsx
@@ -0,0 +1,22 @@
+// @vitest-environment jsdom
+import { describe, it, expect, vi, beforeEach } from "vitest";
+import { runPreviewBatch } from "@/hooks/usePreviewCompression";
+beforeEach(() => vi.restoreAllMocks());
+describe("runPreviewBatch fidelityGate", () => {
+  it("includes fidelityGate:{enabled:true} in every preview payload when on", async () => {
+    const payloads: any[] = [];
+    vi.stubGlobal("fetch", vi.fn(async (_u: string, init: any) => {
+      payloads.push(JSON.parse(init.body));
+      return { ok: true, json: async () => ({
+        original: "o", compressed: "c", originalTokens: 5, compressedTokens: 5, savingsPct: 0,
+        mode: "stacked", durationMs: 1, engineBreakdown: [], diff: [], preservedBlocks: [], ruleRemovals: [],
+      }) } as any;
+    }));
+    await runPreviewBatch({
+      messages: [{ role: "user", content: "x" }],
+      laneEngines: ["rtk"], activeEngines: ["rtk"], fidelityGate: true,
+    });
+    expect(payloads.length).toBe(2); // 1 lane + 1 combined
+    expect(payloads.every((p) => p.fidelityGate?.enabled === true)).toBe(true);
+  });
+});