diff --git a/.github/workflows/e2e.yml b/.github/workflows/e2e.yml
index 78b3d24cb..64205ee26 100644
--- a/.github/workflows/e2e.yml
+++ b/.github/workflows/e2e.yml
@@ -71,6 +71,8 @@ jobs:
         if: always()
         working-directory: apps/api
         env:
+          # Live test: skips the hermetic preload, whose fetch guard would block these calls.
+          RUN_LIVE_TESTS: "1"
           VORTEX_QUOTE_SMOKE_URLS: https://api-staging.vortexfinance.co,https://api.vortexfinance.co
         run: bun test src/tests/deployed-quotes.e2e.test.ts
 
diff --git a/apps/api/src/api/services/phases/blocks/__tests__/brl-onramp-base-cross-chain.transactions.test.ts b/apps/api/src/api/services/phases/blocks/__tests__/brl-onramp-base-cross-chain.transactions.test.ts
index abb8c1b6a..f02564086 100644
--- a/apps/api/src/api/services/phases/blocks/__tests__/brl-onramp-base-cross-chain.transactions.test.ts
+++ b/apps/api/src/api/services/phases/blocks/__tests__/brl-onramp-base-cross-chain.transactions.test.ts
@@ -15,6 +15,7 @@ import { privateKeyToAccount } from "viem/accounts";
 import * as evmFundingNamespace from "../core/evm-funding";
 import * as partnerPricingNamespace from "../../../partners/partner-pricing.service";
 import type { QuoteTicketAttributes } from "../../../../../models/quoteTicket.model";
+import { installFakeChainIdRpc } from "../../../../../test-utils/fake-world/fake-evm";
 import Big from "big.js";
 import { decodeFunctionData, erc20Abi, parseTransaction } from "viem";
 import type { FlowMetadata } from "../core/metadata";
@@ -310,13 +311,15 @@ describe("BRL onramp Base cross-chain transactions", () => {
       type: EphemeralAccountType.EVM
     };
 
-    const presignedTxs = await signUnsignedTransactions(blocks.unsignedTxs, { evmEphemeral });
+    // viem asks the RPC for eth_chainId before signing; any other network use hits the fetch guard.
+    const restoreChainIdRpc = installFakeChainIdRpc();
+    const presignedTxs = await signUnsignedTransactions(blocks.unsignedTxs, { evmEphemeral }).finally(restoreChainIdRpc);
     expect(presignedTxs.length).toBeGreaterThanOrEqual(blocks.unsignedTxs.length);
     expect(presignedTxs.every(tx => typeof tx.txData === "string" && tx.txData.startsWith("0x"))).toBe(true);
     const destinationTransfer = presignedTxs.find(tx => tx.phase === "destinationTransfer");
     expect(destinationTransfer).toBeDefined();
     expect(parseTransaction(destinationTransfer?.txData as `0x${string}`).maxFeePerGas).toBe(3_000_000_000n);
-  }, 60_000);
+  });
 
   it("preserves 18-decimal BSC USDT precision in the destination transfer", async () => {
     const amountRaw = "17500000000000000000";
diff --git a/apps/api/src/api/services/phases/blocks/__tests__/eur-onramp-base-cross-chain.transactions.test.ts b/apps/api/src/api/services/phases/blocks/__tests__/eur-onramp-base-cross-chain.transactions.test.ts
index d2b4cef3f..9d8efaf0e 100644
--- a/apps/api/src/api/services/phases/blocks/__tests__/eur-onramp-base-cross-chain.transactions.test.ts
+++ b/apps/api/src/api/services/phases/blocks/__tests__/eur-onramp-base-cross-chain.transactions.test.ts
@@ -14,6 +14,7 @@ import { privateKeyToAccount } from "viem/accounts";
 import * as evmFundingNamespace from "../core/evm-funding";
 import * as partnerPricingNamespace from "../../../partners/partner-pricing.service";
 import type { QuoteTicketAttributes } from "../../../../../models/quoteTicket.model";
+import { installFakeChainIdRpc } from "../../../../../test-utils/fake-world/fake-evm";
 
 const sharedReal = { ...sharedNamespace };
 const evmFundingReal = { ...evmFundingNamespace };
@@ -185,7 +186,9 @@ describe("EUR onramp Base cross-chain transactions", () => {
     });
 
     const evmEphemeral = { address: EPHEMERAL, secret: PRIVATE_KEY, type: EphemeralAccountType.EVM };
-    const signed = await signUnsignedTransactions(prepared.unsignedTxs, { evmEphemeral });
+    // viem asks the RPC for eth_chainId before signing; any other network use hits the fetch guard.
+    const restoreChainIdRpc = installFakeChainIdRpc();
+    const signed = await signUnsignedTransactions(prepared.unsignedTxs, { evmEphemeral }).finally(restoreChainIdRpc);
     expect(signed.length).toBeGreaterThanOrEqual(prepared.unsignedTxs.length);
     expect(prepared.stateMeta.phaseFlow).toEqual([
       "initial",
@@ -236,5 +239,5 @@ describe("EUR onramp Base cross-chain transactions", () => {
     expect(prepared.unsignedTxs.find(tx => tx.phase === "nablaApprove")?.txData).toMatchObject({ data: "0xc1" });
     expect(prepared.unsignedTxs.find(tx => tx.phase === "squidRouterSwap")?.txData).toMatchObject({ data: "0xa2" });
     expect(prepared.unsignedTxs.find(tx => tx.phase === "backupSquidRouterSwap")?.txData).toMatchObject({ data: "0xb2" });
-  }, 60_000);
+  });
 });
diff --git a/apps/api/src/test-utils/fake-world/fake-evm.ts b/apps/api/src/test-utils/fake-world/fake-evm.ts
index c65b1568b..1e103d396 100644
--- a/apps/api/src/test-utils/fake-world/fake-evm.ts
+++ b/apps/api/src/test-utils/fake-world/fake-evm.ts
@@ -1,5 +1,6 @@
 import { EvmClientManager, type EvmNetworks } from "@vortexfi/shared";
-import { keccak256 } from "viem";
+import { keccak256, toHex } from "viem";
+import { arbitrum, avalanche, base, baseSepolia, bsc, mainnet, polygon, polygonAmoy } from "viem/chains";
 
 export interface RecordedEvmTx {
   network: string;
@@ -35,6 +36,14 @@ const CHAIN_IDS: Record<string, number> = {
 
 const MAX_UINT256 = 2n ** 256n - 1n;
 
+// viem's default public RPC (what a bare http() transport targets, URL-normalized like viem does) → chain id.
+const DEFAULT_RPC_CHAIN_IDS = new Map<string, number>(
+  [arbitrum, avalanche, base, baseSepolia, bsc, mainnet, polygon, polygonAmoy].map(chain => [
+    new URL(chain.rpcUrls.default.http[0]).href,
+    chain.id
+  ])
+);
+
 /**
  * In-memory EVM world standing in for EvmClientManager. Balances are a simple
  * ledger keyed by network/token/holder; transactions are recorded, assigned a
@@ -311,6 +320,31 @@ export class FakeEvm {
   }
 }
 
+/**
+ * Client-side signing (signUnsignedTransactions, also used by the SDK) builds its own viem wallet
+ * clients outside the EvmClientManager seam, and viem's signTransaction asks the RPC for
+ * eth_chainId before signing locally. Answers exactly that call for viem's default public RPCs;
+ * every other request falls through to the fetch guard. Returns the restore function.
+ */
+export function installFakeChainIdRpc(): () => void {
+  const guardedFetch = globalThis.fetch;
+  const fake = (async (input: Parameters<typeof fetch>[0], init?: Parameters<typeof fetch>[1]) => {
+    const url = typeof input === "string" ? input : input instanceof URL ? input.toString() : input.url;
+    const chainId = DEFAULT_RPC_CHAIN_IDS.get(url);
+    if (chainId !== undefined && typeof init?.body === "string") {
+      const payload = JSON.parse(init.body) as { id?: number; method?: string };
+      if (payload.method === "eth_chainId") {
+        return Response.json({ id: payload.id ?? 1, jsonrpc: "2.0", result: toHex(chainId) });
+      }
+    }
+    return guardedFetch(input, init);
+  }) as typeof fetch;
+  globalThis.fetch = Object.assign(fake, guardedFetch);
+  return () => {
+    globalThis.fetch = guardedFetch;
+  };
+}
+
 export function installFakeEvm(): { fakeEvm: FakeEvm; restore: () => void } {
   const original = EvmClientManager.getInstance;
   const fakeEvm = new FakeEvm();
diff --git a/apps/api/src/test-utils/fake-world/fetch-guard.test.ts b/apps/api/src/test-utils/fake-world/fetch-guard.test.ts
new file mode 100644
index 000000000..4024d8563
--- /dev/null
+++ b/apps/api/src/test-utils/fake-world/fetch-guard.test.ts
@@ -0,0 +1,23 @@
+import { describe, expect, it } from "bun:test";
+import { createPublicClient, http } from "viem";
+import { base } from "viem/chains";
+import { installFakeChainIdRpc } from "./fake-evm";
+
+// No installFakeWorld here: the preload alone must keep viem RPC traffic off the network.
+describe("fetch guard", () => {
+  const client = createPublicClient({ chain: base, transport: http(undefined, { retryCount: 0 }) });
+
+  it("rejects viem RPC calls to a real chain", async () => {
+    await expect(client.getChainId()).rejects.toThrow(/Hermetic test violation/);
+  });
+
+  it("lets the fake answer eth_chainId and nothing else", async () => {
+    const restore = installFakeChainIdRpc();
+    try {
+      expect(await client.getChainId()).toBe(base.id);
+      await expect(client.getBlockNumber()).rejects.toThrow(/Hermetic test violation/);
+    } finally {
+      restore();
+    }
+  });
+});
diff --git a/apps/api/src/test-utils/fake-world/fetch-guard.ts b/apps/api/src/test-utils/fake-world/fetch-guard.ts
index ba431afc5..8a2b5d71d 100644
--- a/apps/api/src/test-utils/fake-world/fetch-guard.ts
+++ b/apps/api/src/test-utils/fake-world/fetch-guard.ts
@@ -2,15 +2,17 @@
  * Replaces global fetch with a guard that only allows loopback traffic
  * (the in-process test app). Any other HTTP call is a hermeticity violation
  * and fails with a descriptive error instead of silently reaching a real
- * service.
+ * service. viem's http transport goes through global fetch, so RPC calls are
+ * covered too. The test preload installs it for every hermetic run.
  */
 let originalFetch: typeof fetch | null = null;
 
 const LOOPBACK_PATTERN = /^https?:\/\/(127\.0\.0\.1|localhost|\[::1\])(:|\/|$)/;
 
-export function installFetchGuard(): void {
+/** Returns the uninstaller; a no-op when an outer caller (the preload) already owns the guard. */
+export function installFetchGuard(): () => void {
   if (originalFetch) {
-    return;
+    return () => undefined;
   }
   const realFetch = globalThis.fetch;
   originalFetch = realFetch;
@@ -29,9 +31,10 @@ export function installFetchGuard(): void {
   }) as typeof fetch;
 
   globalThis.fetch = Object.assign(guard, realFetch);
+  return uninstallFetchGuard;
 }
 
-export function uninstallFetchGuard(): void {
+function uninstallFetchGuard(): void {
   if (originalFetch) {
     globalThis.fetch = originalFetch;
     originalFetch = null;
diff --git a/apps/api/src/test-utils/fake-world/index.ts b/apps/api/src/test-utils/fake-world/index.ts
index 2a0f1289d..95052f6fb 100644
--- a/apps/api/src/test-utils/fake-world/index.ts
+++ b/apps/api/src/test-utils/fake-world/index.ts
@@ -1,14 +1,14 @@
 import { ApiManager } from "@vortexfi/shared";
 import { type FakeAlfredpay, type FakeBrla, type FakeMykobo, installFakeAnchors } from "./fake-anchors";
 import { installBackgroundWorkTracking } from "./fake-background-work";
-import { type FakeEvm, installFakeEvm } from "./fake-evm";
+import { type FakeEvm, installFakeChainIdRpc, installFakeEvm } from "./fake-evm";
 import { type FakeMonerium, installFakeMonerium } from "./fake-monerium";
 import { type FakePrices, installFakePrices } from "./fake-prices";
 import { type FakeSquidRouter, installFakeSquidRouter } from "./fake-squidrouter";
-import { installFetchGuard, uninstallFetchGuard } from "./fetch-guard";
+import { installFetchGuard } from "./fetch-guard";
 
 export type { FakeAlfredpay, FakeBrla, FakeEvm, FakeMonerium, FakeMykobo, FakePrices, FakeSquidRouter };
-export { installFetchGuard, uninstallFetchGuard };
+export { installFakeChainIdRpc, installFetchGuard };
 
 export interface FakeWorld {
   evm: FakeEvm;
@@ -28,7 +28,7 @@ export interface FakeWorld {
  * test files in one process, so leaked patches bleed into other files.
  */
 export function installFakeWorld(): FakeWorld {
-  installFetchGuard();
+  const uninstallFetchGuard = installFetchGuard();
   const { fakeEvm, restore: restoreEvm } = installFakeEvm();
   const { fakeAlfredpay, fakeBrla, fakeMykobo, restore: restoreAnchors } = installFakeAnchors();
   const { fakeMonerium, restore: restoreMonerium } = installFakeMonerium();
diff --git a/apps/api/src/test-utils/preload.ts b/apps/api/src/test-utils/preload.ts
index 690778c57..809fb8ced 100644
--- a/apps/api/src/test-utils/preload.ts
+++ b/apps/api/src/test-utils/preload.ts
@@ -71,6 +71,10 @@ if (!process.env.RUN_LIVE_TESTS) {
   process.env.SUBSIDY_SETTLEMENT_DELAY_MS = "25";
   process.env.PHASE_SETTLEMENT_RETRY_BACKOFF_MS = "25";
 
+  // Any real network call (fetch, viem RPC) fails loudly, not only in fake-world tests.
+  const { installFetchGuard } = await import("./fake-world/fetch-guard");
+  installFetchGuard();
+
   // Close the shared Sequelize pool after the whole run so lingering pg
   // connections don't surface as unhandled "Connection terminated" errors.
   const { afterAll } = await import("bun:test");
diff --git a/apps/api/src/tests/aaa-leak-probe.test.ts b/apps/api/src/tests/aaa-leak-probe.test.ts
index b76058717..11b9cfab7 100644
--- a/apps/api/src/tests/aaa-leak-probe.test.ts
+++ b/apps/api/src/tests/aaa-leak-probe.test.ts
@@ -47,8 +47,8 @@ describe("leak canary: no test file leaked a singleton patch", () => {
     }
   });
 
-  it("global fetch is not a leftover fetch guard", () => {
-    expect(globalThis.fetch.name, "the fetch guard was left installed").toBe("fetch");
+  it("global fetch is the preload's fetch guard, not a leftover shim", () => {
+    expect(globalThis.fetch.name, "global fetch was left patched").toBe(process.env.RUN_LIVE_TESTS ? "fetch" : "guard");
   });
 
   it("shared getRoute is not a leftover FakeSquidRouter stub", () => {
diff --git a/apps/api/src/tests/corridors/brl-onramp-crosschain.scenario.test.ts b/apps/api/src/tests/corridors/brl-onramp-crosschain.scenario.test.ts
index bb91a68e4..8b4dba82f 100644
--- a/apps/api/src/tests/corridors/brl-onramp-crosschain.scenario.test.ts
+++ b/apps/api/src/tests/corridors/brl-onramp-crosschain.scenario.test.ts
@@ -25,7 +25,7 @@ import QuoteTicket from "../../models/quoteTicket.model";
 import RampState from "../../models/rampState.model";
 import { resetTestDatabase, setupTestDatabase } from "../../test-utils/db";
 import { createTestTaxId, createTestUser, updatePartnerPricing } from "../../test-utils/factories";
-import { type FakeWorld, installFakeWorld } from "../../test-utils/fake-world";
+import { type FakeWorld, installFakeChainIdRpc, installFakeWorld } from "../../test-utils/fake-world";
 import { installFakeSupabaseAuth, testUserToken } from "../../test-utils/fake-world/fake-auth";
 import { startTestApp, type TestApp } from "../../test-utils/test-app";
 
@@ -41,33 +41,6 @@ const USDC_ON_ARBITRUM = requireToken(Networks.Arbitrum, EvmToken.USDC).erc20Add
 const BRLA_ON_BASE = requireToken(Networks.Base, EvmToken.BRLA).erc20AddressSourceChain as `0x${string}`;
 
 const TAX_ID = "12345678901";
-const BASE_CHAIN_ID_HEX = "0x2105";
-const ARBITRUM_CHAIN_ID_HEX = "0xa4b1";
-
-function installChainIdShim(): { restore: () => void } {
-  const guardedFetch = globalThis.fetch;
-  const shim = (async (input: Parameters<typeof fetch>[0], init?: Parameters<typeof fetch>[1]) => {
-    if (typeof init?.body === "string") {
-      try {
-        const payload = JSON.parse(init.body) as { id?: number; method?: string };
-        if (payload.method === "eth_chainId") {
-          const url = typeof input === "string" ? input : input instanceof URL ? input.toString() : input.url;
-          const chainId = url.includes("base") ? BASE_CHAIN_ID_HEX : ARBITRUM_CHAIN_ID_HEX;
-          return Response.json({ id: payload.id ?? 1, jsonrpc: "2.0", result: chainId });
-        }
-      } catch {
-        // Not a JSON-RPC request; retain the hermetic fetch guard below.
-      }
-    }
-    return guardedFetch(input, init);
-  }) as typeof fetch;
-  globalThis.fetch = Object.assign(shim, guardedFetch);
-  return {
-    restore: () => {
-      globalThis.fetch = guardedFetch;
-    }
-  };
-}
 
 // Unlike the direct pix→BRLA-on-Base corridor, the full swap-and-bridge chain
 // executes here: Nabla swaps the minted BRLA into USDC on Base, the squid
@@ -128,12 +101,12 @@ interface DestinationFundingExpectation {
 describe("BRL onramp cross-chain corridor (pix → Base mint+swap → USDC on Arbitrum)", () => {
   let world: FakeWorld;
   let auth: { restore: () => void };
-  let chainIdShim: { restore: () => void };
+  let restoreChainIdRpc: () => void;
   let app: TestApp;
 
   beforeAll(async () => {
     world = installFakeWorld();
-    chainIdShim = installChainIdShim();
+    restoreChainIdRpc = installFakeChainIdRpc();
     auth = installFakeSupabaseAuth();
     await setupTestDatabase();
     app = await startTestApp();
@@ -142,7 +115,7 @@ describe("BRL onramp cross-chain corridor (pix → Base mint+swap → USDC on Ar
   afterAll(async () => {
     await app?.close();
     auth?.restore();
-    chainIdShim?.restore();
+    restoreChainIdRpc?.();
     world?.restore();
   });
 
diff --git a/apps/api/src/tests/corridors/eur-onramp-monerium.scenario.test.ts b/apps/api/src/tests/corridors/eur-onramp-monerium.scenario.test.ts
index be2d59b19..493790ac1 100644
--- a/apps/api/src/tests/corridors/eur-onramp-monerium.scenario.test.ts
+++ b/apps/api/src/tests/corridors/eur-onramp-monerium.scenario.test.ts
@@ -36,7 +36,7 @@ import QuoteTicket from "../../models/quoteTicket.model";
 import RampState from "../../models/rampState.model";
 import { resetTestDatabase, setupTestDatabase } from "../../test-utils/db";
 import { createTestUser, updatePartnerPricing } from "../../test-utils/factories";
-import { type FakeWorld, installFakeWorld } from "../../test-utils/fake-world";
+import { type FakeWorld, installFakeChainIdRpc, installFakeWorld } from "../../test-utils/fake-world";
 import { installFakeSupabaseAuth, testUserToken } from "../../test-utils/fake-world/fake-auth";
 import { startTestApp, type TestApp } from "../../test-utils/test-app";
 
@@ -49,35 +49,9 @@ const USDC_ON_ARBITRUM = requireToken(Networks.Arbitrum, EvmToken.USDC).erc20Add
 const EURE_ON_POLYGON = MONERIUM_ISSUE_NETWORKS[Networks.Polygon].eureAddress;
 
 const PROFILE_ID = "9e6a92a5-5f6d-48aa-a57b-0f8ae8eb745d";
-const CHAIN_ID_HEX: Record<string, string> = { arbitrum: "0xa4b1", polygon: "0x89" };
 /** Fake Uniswap quoter: 1 EURe (18 decimals) buys 1.16 USDC (6 decimals). */
 const EURE_USDC_RATE_MICRO = 1_160_000n;
 
-function installChainIdShim(): { restore: () => void } {
-  const guardedFetch = globalThis.fetch;
-  const shim = (async (input: Parameters<typeof fetch>[0], init?: Parameters<typeof fetch>[1]) => {
-    if (typeof init?.body === "string") {
-      try {
-        const payload = JSON.parse(init.body) as { id?: number; method?: string };
-        if (payload.method === "eth_chainId") {
-          const url = typeof input === "string" ? input : input instanceof URL ? input.toString() : input.url;
-          const chainId = Object.entries(CHAIN_ID_HEX).find(([name]) => url.includes(name))?.[1] ?? CHAIN_ID_HEX.arbitrum;
-          return Response.json({ id: payload.id ?? 1, jsonrpc: "2.0", result: chainId });
-        }
-      } catch {
-        // Not a JSON-RPC request; retain the hermetic fetch guard below.
-      }
-    }
-    return guardedFetch(input, init);
-  }) as typeof fetch;
-  globalThis.fetch = Object.assign(shim, guardedFetch);
-  return {
-    restore: () => {
-      globalThis.fetch = guardedFetch;
-    }
-  };
-}
-
 const HAPPY_PATH_PHASES: RampPhase[] = [
   "initial",
   "moneriumOnrampMint",
@@ -129,13 +103,13 @@ interface CorridorSetup {
 describe("EUR onramp Monerium corridor (sepa → Polygon mint+swap → USDC on Arbitrum)", () => {
   let world: FakeWorld;
   let auth: { restore: () => void };
-  let chainIdShim: { restore: () => void };
+  let restoreChainIdRpc: () => void;
   let app: TestApp;
   const originalIssueFee = config.monerium.issueFeeEur;
 
   beforeAll(async () => {
     world = installFakeWorld();
-    chainIdShim = installChainIdShim();
+    restoreChainIdRpc = installFakeChainIdRpc();
     auth = installFakeSupabaseAuth();
     await setupTestDatabase();
     app = await startTestApp();
@@ -146,7 +120,7 @@ describe("EUR onramp Monerium corridor (sepa → Polygon mint+swap → USDC on A
     config.monerium.issueFeeEur = originalIssueFee;
     await app?.close();
     auth?.restore();
-    chainIdShim?.restore();
+    restoreChainIdRpc?.();
     world?.restore();
   });
 
diff --git a/apps/api/src/tests/sdk-contract.alfredpay-offramp.test.ts b/apps/api/src/tests/sdk-contract.alfredpay-offramp.test.ts
index 79c614371..f5bbf6125 100644
--- a/apps/api/src/tests/sdk-contract.alfredpay-offramp.test.ts
+++ b/apps/api/src/tests/sdk-contract.alfredpay-offramp.test.ts
@@ -21,11 +21,10 @@ import QuoteTicket from "../models/quoteTicket.model";
 import RampState from "../models/rampState.model";
 import { resetTestDatabase, setupTestDatabase } from "../test-utils/db";
 import { createTestAlfredpayCustomer, createTestApiKey, createTestUser } from "../test-utils/factories";
-import { type FakeWorld, installFakeWorld } from "../test-utils/fake-world";
+import { type FakeWorld, installFakeChainIdRpc, installFakeWorld } from "../test-utils/fake-world";
 import { startTestApp, type TestApp } from "../test-utils/test-app";
 
 const UUID_PATTERN = /^[0-9a-f]{8}-[0-9a-f]{4}-[0-9a-f]{4}-[0-9a-f]{4}-[0-9a-f]{12}$/;
-const POLYGON_CHAIN_ID_HEX = "0x89"; // 137
 
 interface CurrencyCase {
   fiat: FiatToken;
@@ -116,35 +115,6 @@ const FULL_LIFECYCLE_CASES: LifecycleCase[] = [
   }
 ];
 
-/**
- * Same shim as the other SDK contract tests: the SDK's viem wallet client
- * issues one eth_chainId RPC before signing locally. The Alfredpay SELL
- * corridor only ephemeral-signs on Polygon (the source-of-funds transfer is
- * user-broadcast, never SDK-signed), so answer with the Polygon chain id.
- */
-function installChainIdShim(): { restore: () => void } {
-  const guardedFetch = globalThis.fetch;
-  const shim = (async (input: Parameters<typeof fetch>[0], init?: Parameters<typeof fetch>[1]) => {
-    if (typeof init?.body === "string") {
-      try {
-        const payload = JSON.parse(init.body) as { id?: number; method?: string };
-        if (payload.method === "eth_chainId") {
-          return Response.json({ id: payload.id ?? 1, jsonrpc: "2.0", result: POLYGON_CHAIN_ID_HEX });
-        }
-      } catch {
-        // not JSON — let the guarded fetch decide
-      }
-    }
-    return guardedFetch(input, init);
-  }) as typeof fetch;
-  globalThis.fetch = Object.assign(shim, guardedFetch);
-  return {
-    restore: () => {
-      globalThis.fetch = guardedFetch;
-    }
-  };
-}
-
 /**
  * SDK ↔ API contract tests for the Alfredpay SELL rail (USDT on Polygon →
  * USD/MXN/COP/ARS bank payouts): the real SDK lists the user's registered
@@ -155,19 +125,19 @@ function installChainIdShim(): { restore: () => void } {
  */
 describe("SDK ↔ API contract (Alfredpay offramps, USDT on Polygon → bank payout)", () => {
   let world: FakeWorld;
-  let chainIdShim: { restore: () => void };
+  let restoreChainIdRpc: () => void;
   let app: TestApp;
 
   beforeAll(async () => {
     world = installFakeWorld();
-    chainIdShim = installChainIdShim();
+    restoreChainIdRpc = installFakeChainIdRpc();
     await setupTestDatabase();
     app = await startTestApp();
   });
 
   afterAll(async () => {
     await app?.close();
-    chainIdShim?.restore();
+    restoreChainIdRpc?.();
     world?.restore();
   });
 
diff --git a/apps/api/src/tests/sdk-contract.alfredpay-onramp.test.ts b/apps/api/src/tests/sdk-contract.alfredpay-onramp.test.ts
index 0ff347cda..4be2df9d7 100644
--- a/apps/api/src/tests/sdk-contract.alfredpay-onramp.test.ts
+++ b/apps/api/src/tests/sdk-contract.alfredpay-onramp.test.ts
@@ -18,11 +18,10 @@ import QuoteTicket from "../models/quoteTicket.model";
 import RampState from "../models/rampState.model";
 import { resetTestDatabase, setupTestDatabase } from "../test-utils/db";
 import { createTestAlfredpayCustomer, createTestApiKey, createTestUser } from "../test-utils/factories";
-import { type FakeWorld, installFakeWorld } from "../test-utils/fake-world";
+import { type FakeWorld, installFakeChainIdRpc, installFakeWorld } from "../test-utils/fake-world";
 import { startTestApp, type TestApp } from "../test-utils/test-app";
 
 const UUID_PATTERN = /^[0-9a-f]{8}-[0-9a-f]{4}-[0-9a-f]{4}-[0-9a-f]{4}-[0-9a-f]{12}$/;
-const POLYGON_CHAIN_ID_HEX = "0x89"; // 137
 
 interface CurrencyCase {
   fiat: FiatToken;
@@ -98,35 +97,6 @@ const FULL_LIFECYCLE_CASES: CurrencyCase[] = [
   }
 ];
 
-/**
- * Same shim as the other SDK contract tests: the SDK's viem wallet client
- * issues one eth_chainId RPC before signing locally with the ephemeral key.
- * The Alfredpay BUY corridors only ephemeral-sign on Polygon (the anchor mints
- * USDT there), so answer with the Polygon chain id.
- */
-function installChainIdShim(): { restore: () => void } {
-  const guardedFetch = globalThis.fetch;
-  const shim = (async (input: Parameters<typeof fetch>[0], init?: Parameters<typeof fetch>[1]) => {
-    if (typeof init?.body === "string") {
-      try {
-        const payload = JSON.parse(init.body) as { id?: number; method?: string };
-        if (payload.method === "eth_chainId") {
-          return Response.json({ id: payload.id ?? 1, jsonrpc: "2.0", result: POLYGON_CHAIN_ID_HEX });
-        }
-      } catch {
-        // not JSON — let the guarded fetch decide
-      }
-    }
-    return guardedFetch(input, init);
-  }) as typeof fetch;
-  globalThis.fetch = Object.assign(shim, guardedFetch);
-  return {
-    restore: () => {
-      globalThis.fetch = guardedFetch;
-    }
-  };
-}
-
 /**
  * SDK ↔ API contract tests for the Alfredpay BUY rail (fiat → USDT on
  * Polygon): the real @vortexfi/sdk drives the real in-process API. The full
@@ -138,19 +108,19 @@ function installChainIdShim(): { restore: () => void } {
  */
 describe("SDK ↔ API contract (Alfredpay onramps, fiat → USDT on Polygon)", () => {
   let world: FakeWorld;
-  let chainIdShim: { restore: () => void };
+  let restoreChainIdRpc: () => void;
   let app: TestApp;
 
   beforeAll(async () => {
     world = installFakeWorld();
-    chainIdShim = installChainIdShim();
+    restoreChainIdRpc = installFakeChainIdRpc();
     await setupTestDatabase();
     app = await startTestApp();
   });
 
   afterAll(async () => {
     await app?.close();
-    chainIdShim?.restore();
+    restoreChainIdRpc?.();
     world?.restore();
   });
 
diff --git a/apps/api/src/tests/sdk-contract.offramp.test.ts b/apps/api/src/tests/sdk-contract.offramp.test.ts
index 1723f5735..d282dbf51 100644
--- a/apps/api/src/tests/sdk-contract.offramp.test.ts
+++ b/apps/api/src/tests/sdk-contract.offramp.test.ts
@@ -26,7 +26,7 @@ import {
   createTestUser,
   updatePartnerPricing
 } from "../test-utils/factories";
-import { type FakeWorld, installFakeWorld } from "../test-utils/fake-world";
+import { type FakeWorld, installFakeChainIdRpc, installFakeWorld } from "../test-utils/fake-world";
 import { startTestApp, type TestApp } from "../test-utils/test-app";
 
 function requireToken(network: Networks.Base | Networks.Polygon, token: EvmToken) {
@@ -43,35 +43,6 @@ const BRLA_ON_BASE = requireToken(Networks.Base, EvmToken.BRLA).erc20AddressSour
 const TAX_ID = "12345678901";
 const RECEIVER_TAX_ID = "12345678900";
 const PIX_KEY = "test-pix-key";
-const BASE_CHAIN_ID_HEX = "0x2105"; // 8453
-
-/**
- * Same shim as sdk-contract.test.ts: the SDK's viem wallet client issues one
- * eth_chainId RPC before signing locally; the SELL corridor only ephemeral-signs
- * on Base (the Polygon squid leg is user-broadcast, never SDK-signed).
- */
-function installChainIdShim(): { restore: () => void } {
-  const guardedFetch = globalThis.fetch;
-  const shim = (async (input: Parameters<typeof fetch>[0], init?: Parameters<typeof fetch>[1]) => {
-    if (typeof init?.body === "string") {
-      try {
-        const payload = JSON.parse(init.body) as { id?: number; method?: string };
-        if (payload.method === "eth_chainId") {
-          return Response.json({ id: payload.id ?? 1, jsonrpc: "2.0", result: BASE_CHAIN_ID_HEX });
-        }
-      } catch {
-        // not JSON — let the guarded fetch decide
-      }
-    }
-    return guardedFetch(input, init);
-  }) as typeof fetch;
-  globalThis.fetch = Object.assign(shim, guardedFetch);
-  return {
-    restore: () => {
-      globalThis.fetch = guardedFetch;
-    }
-  };
-}
 
 /**
  * SDK ↔ API contract tests for the SELL direction and the user-transaction
@@ -84,19 +55,19 @@ function installChainIdShim(): { restore: () => void } {
  */
 describe("SDK ↔ API contract (BRL offramp, USDC on Polygon → pix)", () => {
   let world: FakeWorld;
-  let chainIdShim: { restore: () => void };
+  let restoreChainIdRpc: () => void;
   let app: TestApp;
 
   beforeAll(async () => {
     world = installFakeWorld();
-    chainIdShim = installChainIdShim();
+    restoreChainIdRpc = installFakeChainIdRpc();
     await setupTestDatabase();
     app = await startTestApp();
   });
 
   afterAll(async () => {
     await app?.close();
-    chainIdShim?.restore();
+    restoreChainIdRpc?.();
     world?.restore();
   });
 
diff --git a/apps/api/src/tests/sdk-contract.test.ts b/apps/api/src/tests/sdk-contract.test.ts
index 7d9850a1f..d30efbe81 100644
--- a/apps/api/src/tests/sdk-contract.test.ts
+++ b/apps/api/src/tests/sdk-contract.test.ts
@@ -14,7 +14,7 @@ import { VortexSdk, VortexSdkError } from "../../../../packages/sdk/src";
 import RampState from "../models/rampState.model";
 import { resetTestDatabase, setupTestDatabase } from "../test-utils/db";
 import { createTestApiKey, createTestTaxId, createTestUser } from "../test-utils/factories";
-import { type FakeWorld, installFakeWorld } from "../test-utils/fake-world";
+import { type FakeWorld, installFakeChainIdRpc, installFakeWorld } from "../test-utils/fake-world";
 import { startTestApp, type TestApp } from "../test-utils/test-app";
 
 function requireBrlaOnBase() {
@@ -28,40 +28,6 @@ const brlaTokenDetails = requireBrlaOnBase();
 const BRLA_ON_BASE = brlaTokenDetails.erc20AddressSourceChain as `0x${string}`;
 
 const UUID_PATTERN = /^[0-9a-f]{8}-[0-9a-f]{4}-[0-9a-f]{4}-[0-9a-f]{4}-[0-9a-f]{12}$/;
-const BASE_CHAIN_ID_HEX = "0x2105"; // 8453
-
-/**
- * The SDK signs EVM transactions through a real viem wallet client, and viem's
- * signTransaction issues a single eth_chainId RPC before signing locally with
- * the ephemeral key. Answer that one call in-memory (the corridor only signs on
- * Base) and let every other request fall through to the fetch guard, so any
- * genuine network use still fails loudly. The SDK's NetworkManager itself is
- * inert here: it only opens chain WebSockets when signing Pendulum, Moonbeam,
- * or Hydration transactions, and the direct BRL→BRLA-on-Base corridor produces
- * a single Base EVM transaction.
- */
-function installChainIdShim(): { restore: () => void } {
-  const guardedFetch = globalThis.fetch;
-  const shim = (async (input: Parameters<typeof fetch>[0], init?: Parameters<typeof fetch>[1]) => {
-    if (typeof init?.body === "string") {
-      try {
-        const payload = JSON.parse(init.body) as { id?: number; method?: string };
-        if (payload.method === "eth_chainId") {
-          return Response.json({ id: payload.id ?? 1, jsonrpc: "2.0", result: BASE_CHAIN_ID_HEX });
-        }
-      } catch {
-        // not JSON — let the guarded fetch decide
-      }
-    }
-    return guardedFetch(input, init);
-  }) as typeof fetch;
-  globalThis.fetch = Object.assign(shim, guardedFetch);
-  return {
-    restore: () => {
-      globalThis.fetch = guardedFetch;
-    }
-  };
-}
 
 /**
  * SDK ↔ API contract tests: the real @vortexfi/sdk (imported from source)
@@ -71,19 +37,21 @@ function installChainIdShim(): { restore: () => void } {
  */
 describe("SDK ↔ API contract (BRL onramp, pix → BRLA on Base)", () => {
   let world: FakeWorld;
-  let chainIdShim: { restore: () => void };
+  let restoreChainIdRpc: () => void;
   let app: TestApp;
 
   beforeAll(async () => {
     world = installFakeWorld();
-    chainIdShim = installChainIdShim();
+    // The SDK's NetworkManager stays inert: it only opens chain WebSockets for Pendulum,
+    // Moonbeam, or Hydration signing, and this corridor signs a single Base EVM transaction.
+    restoreChainIdRpc = installFakeChainIdRpc();
     await setupTestDatabase();
     app = await startTestApp();
   });
 
   afterAll(async () => {
     await app?.close();
-    chainIdShim?.restore();
+    restoreChainIdRpc?.();
     world?.restore();
   });
 
diff --git a/docs/operations-testing.md b/docs/operations-testing.md
index 17f07dde0..53fc98215 100644
--- a/docs/operations-testing.md
+++ b/docs/operations-testing.md
@@ -277,9 +277,11 @@ Tests that hit real RPCs or sandboxes (e.g. XCM dry-runs in `packages/shared`) a
 `RUN_LIVE_TESTS=1` via `describe.skipIf`. They are for local debugging and optional nightly runs,
 never PR-blocking.
 
-The e2e workflow sets `VORTEX_QUOTE_SMOKE_URLS` for `deployed-quotes.e2e.test.ts`, which requires
-successful cross-chain BUY and SELL quotes from both staging and production. Ordinary local and
-PR-blocking API runs leave the variable unset, so this deployment smoke test does not make them
+The e2e workflow sets `VORTEX_QUOTE_SMOKE_URLS` and `RUN_LIVE_TESTS=1` for
+`deployed-quotes.e2e.test.ts`, which requires successful cross-chain BUY and SELL quotes from both
+staging and production. `RUN_LIVE_TESTS=1` is required: without it the test preload installs the
+fetch guard, which rejects the calls to the deployed APIs. Ordinary local and PR-blocking API runs
+leave `VORTEX_QUOTE_SMOKE_URLS` unset, so this deployment smoke test does not make them
 network-dependent.
 
 ### External API contracts (`apps/api/src/tests/contracts/`)