diff --git a/config/quality/complexity-baseline.json b/config/quality/complexity-baseline.json
index 561236c948..070f1b8ed5 100644
--- a/config/quality/complexity-baseline.json
+++ b/config/quality/complexity-baseline.json
@@ -2,6 +2,7 @@
   "_comment": "Catraca de complexidade (check-complexity.mjs, ESLint core rules complexity>=15 e max-lines-per-function>80 sobre src+open-sse+electron+bin via eslint.complexity.config.mjs). Conta total de violacoes; so pode cair. --update ratcheta.",
   "count": 1896,
   "_rebaseline_2026_06_20_postlote_concurrent_drift": "Reconciliacao release-volatil: 1895->1896 (+1). Drift de condicional NOVO de PRs mergeados pela sessao concorrente APOS o #4338 ratchetar para 1895 (#4355 pricing gpt-5.x-pro / #4364 cli active-context cred / #4363 compliance cleanup / #4358 mitm mask / #4332 injection-guard-16KB). O fast-path do release nao roda check:complexity (so release->main), entao o ramo acumula sem rebaselinar. Medido com `node scripts/check/check-complexity.mjs` no tip cdfd71c17. Mesma familia — crescimento de feature legitimo, nao regressao.",
+  "_note_2026_06_20_4371_chatcore_heap_leaf": "PR #4371 (extract checkHeapPressureGuard leaf, god-file decomposition start) e complexity-NEUTRO: handleChatCore so PERDE codigo e o novo heapPressure.ts checkHeapPressureGuard fica sob o teto — a contagem permanece 1896 (medido no tip mesclado com check-complexity.mjs).",
   "_ratchet_2026_06_19_phasecombosetup_fix": "1896->1895 (-1, ratchet DOWN — melhoria, NAO reconciliacao). O #4336 reconciliou o drift do lote para 1896 INCLUINDO a violacao que o #4326 (ComboContext) introduziu: phaseComboSetup media complexity 17 (>15) porque a extracao concentrou os condicionais de pinning/ternarios numa funcao que estourava o teto (irônico p/ uma decomposicao). Este PR CORRIGE na origem — extrai resolveContextCachePin (helper do pinning), phaseComboSetup volta a <15 — baixando a contagem 1. Medido com `node scripts/check/check-complexity.mjs` no tip pos-#4336.",
   "_rebaseline_2026_06_19_lote3_postdeploy_drift": "Reconciliacao release-volatil pos-merge do lote adicional (6 PRs apos o deploy): 1890->1896 (+6). Drift de condicionais NOVOS de #4327 (per-key USD usage quotas — apiKeyUsageLimits.ts + validation/policy branches), #4334 (cache-aware compression guard) e #4326 (phaseComboSetup extraido). Medido no tip real da release com `node scripts/check/check-complexity.mjs`. Mesma familia/justificativa do _rebaseline_2026_06_19_lote3_merge_drift abaixo — feature legitima, nao regressao.",
   "_rebaseline_2026_06_19_lote3_merge_drift": "Reconciliacao release-volatil pos-merge do lote de 13 PRs (release/v3.8.30): 1888->1890 (+2). Drift de condicionais NOVOS trazidos por #4313 (5 harvested features — combo allowlist intersection, serviceKind filter) e #4323 (compression e2e — novos ramos em ultra/aggressive/gcf/strategySelector), merges que entraram DEPOIS do #4318 medir 1888. O fast-path do release nao roda check:complexity (so release->main), entao os ramos acumulam sem rebaselinar. Medido no tip real da release pos-merge com `node scripts/check/check-complexity.mjs`. Mesma familia dos rebaselines anteriores — crescimento de feature legitimo, nao regressao; reducao fica como debt de refactor dedicado.",
diff --git a/open-sse/handlers/chatCore.ts b/open-sse/handlers/chatCore.ts
index f01e763185..76eb361ca1 100644
--- a/open-sse/handlers/chatCore.ts
+++ b/open-sse/handlers/chatCore.ts
@@ -41,7 +41,7 @@ import {
   resolveMemoryOwnerId,
 } from "./chatCore/memoryExtraction.ts";
 import { CORS_HEADERS } from "../utils/cors.ts";
-import { HEAP_PRESSURE_THRESHOLD_MB } from "../utils/heapPressure.ts";
+import { checkHeapPressureGuard } from "../utils/heapPressure.ts";
 import { normalizeHeaders } from "../utils/headers.ts";
 import { detectFormatFromEndpoint, getTargetFormat } from "../services/provider.ts";
 import { injectSystemPrompt } from "../services/systemPrompt.ts";
@@ -643,27 +643,8 @@ export async function handleChatCore({
   // cascading OOM when many large-context requests arrive concurrently.
   try {
     const heapUsedMB = process.memoryUsage().heapUsed / (1024 * 1024);
-    if (heapUsedMB > HEAP_PRESSURE_THRESHOLD_MB) {
-      // Internal telemetry only — never expose the heap figure to clients (Hard Rule #12).
-      console.warn(
-        `[chatCore] heap pressure guard tripped: ${Math.round(heapUsedMB)}MB > ${HEAP_PRESSURE_THRESHOLD_MB}MB; returning 503`
-      );
-      return {
-        success: false,
-        status: 503,
-        error: "Service temporarily unavailable due to resource pressure. Retry shortly.",
-        response: new Response(
-          JSON.stringify({
-            error: {
-              message: "Service temporarily unavailable due to resource pressure. Retry shortly.",
-              type: "server_error",
-              code: "heap_pressure",
-            },
-          }),
-          { status: 503, headers: { "Content-Type": "application/json", "Retry-After": "5" } }
-        ),
-      };
-    }
+    const heapGuard = checkHeapPressureGuard(heapUsedMB);
+    if (heapGuard) return heapGuard;
   } catch {
     /* memoryUsage() never throws */
   }
diff --git a/open-sse/utils/heapPressure.ts b/open-sse/utils/heapPressure.ts
index 85f6050d2c..659853356d 100644
--- a/open-sse/utils/heapPressure.ts
+++ b/open-sse/utils/heapPressure.ts
@@ -42,3 +42,40 @@ export const HEAP_PRESSURE_THRESHOLD_MB = computeHeapPressureThresholdMb(
   v8.getHeapStatistics().heap_size_limit / (1024 * 1024),
   process.env.HEAP_PRESSURE_THRESHOLD_MB
 );
+
+const HEAP_PRESSURE_MESSAGE =
+  "Service temporarily unavailable due to resource pressure. Retry shortly.";
+
+export type HeapPressureGuardResult = {
+  success: false;
+  status: 503;
+  error: string;
+  response: Response;
+};
+
+/**
+ * Memory-pressure shed guard for the chat pipeline (extracted from chatCore's handleChatCore).
+ * Returns a ready-to-return 503 result when live heap usage exceeds the shed threshold, else null
+ * to proceed. The heap figure is logged for INTERNAL telemetry only and is NEVER placed in the
+ * client-facing response (Hard Rule #12). Behaviour is byte-identical to the previous inline guard.
+ */
+export function checkHeapPressureGuard(
+  heapUsedMb: number,
+  thresholdMb: number = HEAP_PRESSURE_THRESHOLD_MB
+): HeapPressureGuardResult | null {
+  if (heapUsedMb <= thresholdMb) return null;
+  console.warn(
+    `[chatCore] heap pressure guard tripped: ${Math.round(heapUsedMb)}MB > ${thresholdMb}MB; returning 503`
+  );
+  return {
+    success: false,
+    status: 503,
+    error: HEAP_PRESSURE_MESSAGE,
+    response: new Response(
+      JSON.stringify({
+        error: { message: HEAP_PRESSURE_MESSAGE, type: "server_error", code: "heap_pressure" },
+      }),
+      { status: 503, headers: { "Content-Type": "application/json", "Retry-After": "5" } }
+    ),
+  };
+}
diff --git a/tests/unit/heap-pressure.test.ts b/tests/unit/heap-pressure.test.ts
index 621b1ea712..0f3fd0f0d7 100644
--- a/tests/unit/heap-pressure.test.ts
+++ b/tests/unit/heap-pressure.test.ts
@@ -1,6 +1,9 @@
 import { describe, it } from "node:test";
 import assert from "node:assert/strict";
-import { computeHeapPressureThresholdMb } from "../../open-sse/utils/heapPressure.ts";
+import {
+  checkHeapPressureGuard,
+  computeHeapPressureThresholdMb,
+} from "../../open-sse/utils/heapPressure.ts";
 
 // Regression guard for the v3.8.8 "Service temporarily unavailable due to resource
 // pressure" outage: a fixed 200MB threshold sat below the app's ~260MB working set,
@@ -46,3 +49,33 @@ describe("computeHeapPressureThresholdMb", () => {
     }
   });
 });
+
+// Extracted from chatCore's handleChatCore (god-file decomposition, first leaf). The SET of
+// behaviours below is byte-identical to the previous inline guard.
+describe("checkHeapPressureGuard", () => {
+  it("returns null (proceed) when heap usage is at or below the threshold", () => {
+    assert.equal(checkHeapPressureGuard(100, 256), null);
+    assert.equal(checkHeapPressureGuard(256, 256), null, "boundary: == threshold proceeds");
+  });
+
+  it("returns a 503 shed result when heap usage exceeds the threshold", async () => {
+    const guard = checkHeapPressureGuard(300, 256);
+    assert.ok(guard, "must shed above threshold");
+    assert.equal(guard.success, false);
+    assert.equal(guard.status, 503);
+    assert.equal(guard.response.status, 503);
+    assert.equal(guard.response.headers.get("Retry-After"), "5");
+    assert.equal(guard.response.headers.get("Content-Type"), "application/json");
+    const payload = await guard.response.json();
+    assert.equal(payload.error.code, "heap_pressure");
+    assert.equal(payload.error.type, "server_error");
+  });
+
+  it("never leaks the heap figure to the client response (Hard Rule #12)", async () => {
+    const guard = checkHeapPressureGuard(987, 256);
+    assert.ok(guard);
+    const text = JSON.stringify(await guard.response.clone().json()) + (guard.error ?? "");
+    assert.ok(!text.includes("987"), "the measured heap MB must not appear in the client payload");
+    assert.ok(!/\bMB\b/.test(text), "no heap-size detail should reach the client");
+  });
+});