diff --git a/open-sse/services/compression/types.ts b/open-sse/services/compression/types.ts
index 3331aa6f69..0dd2c73cbd 100644
--- a/open-sse/services/compression/types.ts
+++ b/open-sse/services/compression/types.ts
@@ -11,6 +11,7 @@
 
 import { ENGINE_IDS } from "./engineCatalog.ts";
 import type { ContextBudgetConfig } from "./adaptiveCompression/types.ts";
+import type { FidelityGateConfig } from "./fidelityGate.ts";
 
 // Re-export so consumers that already import from this module (e.g. src/lib/db/compression.ts)
 // can get ENGINE_IDS without a second bare `@omniroute/open-sse/...engineCatalog.ts` specifier.
@@ -141,6 +142,8 @@ export interface CompressionConfig {
   comboOverrides: Record<string, CompressionMode>;
   compressionComboId?: string | null;
   stackedPipeline?: CompressionPipelineStep[];
+  /** Opt-in per-step fidelity gate (default disabled). */
+  fidelityGate?: FidelityGateConfig;
   cavemanConfig?: CavemanConfig;
   cavemanOutputMode?: CavemanOutputModeConfig;
   /** Phase 4A: selected output styles (supersedes cavemanOutputMode via a back-compat shim). */
@@ -232,6 +235,8 @@ export interface CompressionStats {
     techniquesUsed: string[];
     rulesApplied?: string[];
     durationMs?: number;
+    rejected?: boolean;
+    rejectReason?: string;
   }>;
 }
 
diff --git a/tests/unit/compression/fidelityGateTypes.test.ts b/tests/unit/compression/fidelityGateTypes.test.ts
new file mode 100644
index 0000000000..cb71f4ae3c
--- /dev/null
+++ b/tests/unit/compression/fidelityGateTypes.test.ts
@@ -0,0 +1,13 @@
+import test from "node:test";
+import assert from "node:assert/strict";
+import type { CompressionConfig, CompressionStats } from "../../../open-sse/services/compression/types.ts";
+import type { FidelityGateConfig } from "../../../open-sse/services/compression/fidelityGate.ts";
+test("CompressionConfig accepts a fidelityGate block and breakdown carries rejected fields", () => {
+  const cfg: CompressionConfig = { fidelityGate: { enabled: true } as FidelityGateConfig };
+  assert.equal(cfg.fidelityGate?.enabled, true);
+  const entry: NonNullable<CompressionStats["engineBreakdown"]>[number] = {
+    engine: "caveman", originalTokens: 10, compressedTokens: 10, savingsPercent: 0,
+    techniquesUsed: [], rejected: true, rejectReason: "numeric: 14 ausente",
+  };
+  assert.equal(entry.rejected, true);
+});