diff --git a/src/config/proxy-env.ts b/src/config/proxy-env.ts
index adbfe5f6176..f096cd3885a 100644
--- a/src/config/proxy-env.ts
+++ b/src/config/proxy-env.ts
@@ -98,6 +98,37 @@ function warnProxyConfigDiscardOnce(kind: "proxy" | "noProxy" | "noProxyElements
   }
 }
 
+// Loopback only has a proxy to bypass when the environment already carries proxy state.
+// Writing NO_PROXY into a proxy-free process is itself a proxy-env mutation that callers
+// observe (the lab sandbox rejects any of these keys as a forbidden leak), so the
+// early-return merge runs only when one is already present.
+const PROXY_STATE_ENV_KEYS = [
+  "HTTP_PROXY", "HTTPS_PROXY", "ALL_PROXY", "NO_PROXY",
+  "http_proxy", "https_proxy", "all_proxy", "no_proxy",
+] as const;
+
+function ambientProxyStateExists(): boolean {
+  for (const key of PROXY_STATE_ENV_KEYS) {
+    const value = process.env[key];
+    if (value !== undefined && value !== "") return true;
+  }
+  return false;
+}
+
+function mergeNoProxyEntries(configured: string[] = []): void {
+  const existing = process.env.NO_PROXY ?? process.env.no_proxy ?? "";
+  const entries = existing.split(",").map(s => s.trim()).filter(Boolean);
+  const seen = new Set(entries.map(entry => entry.toLowerCase()));
+  for (const host of [...configured, "localhost", "127.0.0.1", "::1", "[::1]"]) {
+    const key = host.toLowerCase();
+    if (!seen.has(key)) {
+      entries.push(host);
+      seen.add(key);
+    }
+  }
+  process.env.NO_PROXY = entries.join(",");
+}
+
 /**
  * Mirror `config.proxy` into HTTP(S)_PROXY env vars. Bun fetch consumes them natively; transports
  * such as the ChatGPT upstream WebSocket select the same environment explicitly. User-set HTTP(S)_PROXY
@@ -130,6 +161,11 @@ export function applyProxyEnvWith(
   let proxy = typeof rawProxy === "string" ? resolveEnvValue(rawProxy) : undefined;
   if (!proxy) {
     if (rawProxy !== undefined) warnProxyConfigDiscardOnce("proxy");
+    // Ambient-proxy path: only loopback bypasses are appended. A configured noProxy is
+    // deliberately NOT merged here — with no config.proxy the operator's bypass list has
+    // no declared proxy to apply against, and merging it would silently widen direct
+    // egress beyond the loopback fix this branch exists for.
+    if (ambientProxyStateExists()) mergeNoProxyEntries();
     configureSocks5Fetch();
     return;
   }
@@ -178,9 +214,6 @@ export function applyProxyEnvWith(
       if (!process.env.HTTPS_PROXY?.trim() && !process.env.https_proxy?.trim()) process.env.HTTPS_PROXY = proxy;
     }
   }
-  const existing = process.env.NO_PROXY ?? process.env.no_proxy ?? "";
-  const entries = existing.split(",").map(s => s.trim()).filter(Boolean);
-  const seen = new Set(entries.map(e => e.toLowerCase()));
   // Configured entries first, then loopback: loopback is unconditional, so appending it last
   // keeps it present even when the operator lists a loopback host themselves.
   const raw = config.noProxy;
@@ -200,13 +233,6 @@ export function applyProxyEnvWith(
   const configured = configuredEntries
     .map(entry => entry.trim())
     .filter(Boolean);
-  for (const host of [...configured, "localhost", "127.0.0.1", "::1", "[::1]"]) {
-    const key = host.toLowerCase();
-    if (!seen.has(key)) {
-      entries.push(host);
-      seen.add(key);
-    }
-  }
-  process.env.NO_PROXY = entries.join(",");
+  mergeNoProxyEntries(configured);
   configureSocks5Fetch();
 }
diff --git a/structure/config.md b/structure/config.md
index 12cf9acbd10..3a8f573bb29 100644
--- a/structure/config.md
+++ b/structure/config.md
@@ -542,7 +542,9 @@ Stored Direct substitution follows the [credential identity contract](providers/
 configuration. An explicit SOCKS5 or SOCKS5h URL selects ALL_PROXY and removes
 stale scheme-proxy variables; HTTP(S) settings retain their existing environment
 precedence. Activation keeps the existing Windows auto-discovery path and loopback
-NO_PROXY entries. When the environment no longer selects SOCKS, activation
+NO_PROXY entries; the no-configured-proxy return merges them only when the environment
+already carries proxy state, leaving a proxy-free process untouched. When the
+environment no longer selects SOCKS, activation
 restores the native fetch; removing a saved field alone does not erase inherited
 process environment variables.
 SOCKS4 is rejected instead of being advertised as a working transport.
diff --git a/tests/server/proxy-env.test.ts b/tests/server/proxy-env.test.ts
index 340454dcfb6..ca1016b16cf 100644
--- a/tests/server/proxy-env.test.ts
+++ b/tests/server/proxy-env.test.ts
@@ -1,7 +1,7 @@
 import { afterEach, beforeEach, describe, expect, test } from "bun:test";
 import { createServer } from "node:http";
 import { applyProxyEnv } from "../../src/config";
-import { resolveProxyRoute, configureSocks5Fetch } from "../../src/lib/proxy-env";
+import { configuredOutboundFetch, resolveProxyRoute, configureSocks5Fetch } from "../../src/lib/proxy-env";
 import type { OcxConfig } from "../../src/types";
 
 const PROXY_ENV_KEYS = ["HTTP_PROXY", "HTTPS_PROXY", "ALL_PROXY", "NO_PROXY", "http_proxy", "https_proxy", "all_proxy", "no_proxy", "OCX_TEST_PROXY_REF", "OCX_TEST_NO_PROXY_REF"] as const;
@@ -215,12 +215,45 @@ describe("applyProxyEnv with values the schema does not constrain", () => {
 });
 
 describe("applyProxyEnv", () => {
-  test("no-op when config.proxy is unset", () => {
+  test("writes no proxy state into an environment that has none", () => {
+    applyProxyEnv(configWithProxy());
+    for (const key of PROXY_ENV_KEYS) {
+      expect(process.env[key]).toBeUndefined();
+    }
+  });
+
+  test("keeps mandatory loopback exclusions when config.proxy is unset", () => {
     process.env.NO_PROXY = "operator-owned.example";
     applyProxyEnv(configWithProxy(undefined, "internal.example"));
     expect(process.env.HTTP_PROXY).toBeUndefined();
     expect(process.env.HTTPS_PROXY).toBeUndefined();
-    expect(process.env.NO_PROXY).toBe("operator-owned.example");
+    expect(process.env.NO_PROXY).toBe("operator-owned.example,localhost,127.0.0.1,::1,[::1]");
+  });
+
+  test.each(["ALL_PROXY", "all_proxy"])("inherited SOCKS %s cannot intercept loopback fetches", async key => {
+    process.env[key] = "socks5://untrusted-proxy.invalid:1080";
+    applyProxyEnv(configWithProxy());
+    let directCalls = 0;
+    const response = await configuredOutboundFetch("http://127.0.0.1:11434/v1/chat/completions", undefined, async () => {
+      directCalls += 1;
+      return new Response("direct");
+    });
+    expect(await response.text()).toBe("direct");
+    expect(directCalls).toBe(1);
+  });
+
+  test.each(["ALL_PROXY", "all_proxy"])("inherited SOCKS %s still owns non-loopback fetches", async key => {
+    process.env[key] = "socks5://untrusted-proxy.invalid:1080";
+    applyProxyEnv(configWithProxy());
+    // The bypass must be scoped to loopback only: a non-loopback URL still routes through
+    // the inherited SOCKS proxy, which fails here because the proxy is unreachable. The
+    // direct fallback must NOT be consulted — if it were, the bypass leaked.
+    let directCalls = 0;
+    await expect(configuredOutboundFetch("http://api.example.com/v1/chat/completions", undefined, async () => {
+      directCalls += 1;
+      return new Response("direct");
+    })).rejects.toThrow();
+    expect(directCalls).toBe(0);
   });
 
   test("merges configured comma-separated noProxy entries", () => {