diff --git a/open-sse/handlers/chatCore.ts b/open-sse/handlers/chatCore.ts
index de4b63a1e1..81c69ae8e5 100644
--- a/open-sse/handlers/chatCore.ts
+++ b/open-sse/handlers/chatCore.ts
@@ -166,6 +166,7 @@ import {
   mergeResponseToolNameMap,
 } from "./chatCore/passthroughToolNames.ts";
 import { recordContextEditingTelemetryHook } from "./chatCore/contextEditingTelemetry.ts";
+import { recordCompressionCacheStats } from "./chatCore/compressionCacheStats.ts";
 import {
   appendNonStreamingSseTerminalSignal,
   type NonStreamingSseTerminalState,
@@ -1362,39 +1363,15 @@ export async function handleChatCore({
           }
 
           if (result.compressed) {
-            void (async () => {
-              try {
-                const { detectCachingContext } =
-                  await import("../services/compression/cachingAware.ts");
-                const { recordCacheStats } =
-                  await import("../../src/lib/db/compressionCacheStats.ts");
-                const cacheContext = detectCachingContext(compressionInputBody, {
-                  provider,
-                  targetFormat,
-                  model: effectiveModel,
-                });
-                const tokensSavedCompression = Math.max(
-                  0,
-                  result.stats.originalTokens - result.stats.compressedTokens
-                );
-                recordCacheStats({
-                  provider: cacheContext.provider ?? provider ?? "unknown",
-                  model: effectiveModel ?? "",
-                  compressionMode: mode,
-                  cacheControlPresent: cacheContext.hasCacheControl,
-                  estimatedCacheHit: cacheContext.hasCacheControl && cacheContext.isCachingProvider,
-                  tokensSavedCompression,
-                  tokensSavedCaching: 0,
-                  netSavings: tokensSavedCompression,
-                });
-              } catch (err) {
-                log?.debug?.(
-                  "COMPRESSION",
-                  "Compression cache stats write skipped: " +
-                    (err instanceof Error ? err.message : String(err))
-                );
-              }
-            })();
+            recordCompressionCacheStats({
+              compressionInputBody,
+              provider,
+              targetFormat,
+              effectiveModel,
+              mode,
+              stats: result.stats,
+              log,
+            });
             log?.info?.(
               "COMPRESSION",
               `Prompt compressed (${mode}): ${result.stats.originalTokens} -> ${result.stats.compressedTokens} tokens (${result.stats.savingsPercent}% saved, techniques: ${result.stats.techniquesUsed.join(",")})`
diff --git a/open-sse/handlers/chatCore/compressionCacheStats.ts b/open-sse/handlers/chatCore/compressionCacheStats.ts
new file mode 100644
index 0000000000..06bca10837
--- /dev/null
+++ b/open-sse/handlers/chatCore/compressionCacheStats.ts
@@ -0,0 +1,53 @@
+/**
+ * chatCore compression cache-stats hook (Quality Gate v2 / Fase 9 — chatCore god-file
+ * decomposition, #3501).
+ *
+ * Extracted from handleChatCore's request-setup compression path: when a prompt was compressed,
+ * record the caching-context cache-stats receipt (estimated cache hit + tokens saved). Best-effort,
+ * fire-and-forget — the inner work is an un-awaited IIFE that swallows its own errors and never
+ * affects the request. Behaviour is byte-identical to the previous inline block.
+ */
+
+type LoggerLike = { debug?: (...args: unknown[]) => void } | null | undefined;
+
+export function recordCompressionCacheStats(args: {
+  compressionInputBody: unknown;
+  provider: string | null | undefined;
+  targetFormat: string | null | undefined;
+  effectiveModel: string | null | undefined;
+  mode: string;
+  stats: { originalTokens: number; compressedTokens: number };
+  log?: LoggerLike;
+}): void {
+  void (async () => {
+    try {
+      const { detectCachingContext } = await import("../../services/compression/cachingAware.ts");
+      const { recordCacheStats } = await import("@/lib/db/compressionCacheStats");
+      const cacheContext = detectCachingContext(args.compressionInputBody, {
+        provider: args.provider,
+        targetFormat: args.targetFormat,
+        model: args.effectiveModel,
+      });
+      const tokensSavedCompression = Math.max(
+        0,
+        args.stats.originalTokens - args.stats.compressedTokens
+      );
+      recordCacheStats({
+        provider: cacheContext.provider ?? args.provider ?? "unknown",
+        model: args.effectiveModel ?? "",
+        compressionMode: args.mode,
+        cacheControlPresent: cacheContext.hasCacheControl,
+        estimatedCacheHit: cacheContext.hasCacheControl && cacheContext.isCachingProvider,
+        tokensSavedCompression,
+        tokensSavedCaching: 0,
+        netSavings: tokensSavedCompression,
+      });
+    } catch (err) {
+      args.log?.debug?.(
+        "COMPRESSION",
+        "Compression cache stats write skipped: " +
+          (err instanceof Error ? err.message : String(err))
+      );
+    }
+  })();
+}
diff --git a/tests/unit/chatcore-compression-cache-stats.test.ts b/tests/unit/chatcore-compression-cache-stats.test.ts
new file mode 100644
index 0000000000..fe1e3904b2
--- /dev/null
+++ b/tests/unit/chatcore-compression-cache-stats.test.ts
@@ -0,0 +1,90 @@
+// Characterization of recordCompressionCacheStats — the compression cache-stats hook extracted
+// from handleChatCore's request-setup compression path (chatCore god-file decomposition, #3501).
+// Fire-and-forget; uses a real temp DB and polls compression_cache_stats. Locks: a compressed
+// prompt records a cache-stats row with the resolved provider/mode/tokens-saved, and the helper
+// returns synchronously without throwing (fail-open).
+import { test, before, after } from "node:test";
+import assert from "node:assert/strict";
+import fs from "node:fs";
+import os from "node:os";
+import path from "node:path";
+
+const testDataDir = fs.mkdtempSync(path.join(os.tmpdir(), "omni-comp-cache-test-"));
+process.env.DATA_DIR = testDataDir;
+
+const coreDb = await import("../../src/lib/db/core.ts");
+const { recordCompressionCacheStats } = await import(
+  "../../open-sse/handlers/chatCore/compressionCacheStats.ts"
+);
+
+function rowsFor(provider: string): Array<Record<string, unknown>> {
+  return coreDb
+    .getDbInstance()
+    .prepare(
+      "SELECT provider, compression_mode AS mode, tokens_saved_compression AS saved FROM compression_cache_stats WHERE provider = ?"
+    )
+    .all(provider) as Array<Record<string, unknown>>;
+}
+
+async function waitForRows(provider: string, min: number, timeoutMs = 3000) {
+  const deadline = Date.now() + timeoutMs;
+  while (Date.now() < deadline) {
+    if (rowsFor(provider).length >= min) break;
+    await new Promise((r) => setTimeout(r, 25));
+  }
+  return rowsFor(provider);
+}
+
+before(async () => {
+  await coreDb.ensureDbInitialized();
+});
+
+after(() => {
+  coreDb.resetDbInstance();
+  try {
+    fs.rmSync(testDataDir, { recursive: true, force: true });
+  } catch {
+    // best-effort cleanup
+  }
+});
+
+test("returns synchronously without throwing (fire-and-forget)", () => {
+  assert.doesNotThrow(() =>
+    recordCompressionCacheStats({
+      compressionInputBody: { messages: [{ role: "user", content: "hi" }] },
+      provider: "openai",
+      targetFormat: "openai",
+      effectiveModel: "gpt-x",
+      mode: "balanced",
+      stats: { originalTokens: 100, compressedTokens: 60 },
+    })
+  );
+});
+
+test("records a cache-stats row with the resolved provider/mode/tokens-saved", async () => {
+  recordCompressionCacheStats({
+    compressionInputBody: { messages: [{ role: "user", content: "hello world" }] },
+    provider: "ccs-prov",
+    targetFormat: "openai",
+    effectiveModel: "gpt-ccs",
+    mode: "aggressive",
+    stats: { originalTokens: 200, compressedTokens: 75 },
+  });
+  const rows = await waitForRows("ccs-prov", 1);
+  assert.equal(rows.length, 1);
+  assert.equal(rows[0].mode, "aggressive");
+  assert.equal(rows[0].saved, 125);
+});
+
+test("clamps negative tokens-saved to 0", async () => {
+  recordCompressionCacheStats({
+    compressionInputBody: { messages: [] },
+    provider: "ccs-neg",
+    targetFormat: "openai",
+    effectiveModel: "gpt-x",
+    mode: "balanced",
+    stats: { originalTokens: 50, compressedTokens: 80 },
+  });
+  const rows = await waitForRows("ccs-neg", 1);
+  assert.equal(rows[0].saved, 0);
+});