diff --git a/tests/fixtures/adapta-web-stream-error-boundary.fixture.ts b/tests/fixtures/adapta-web-stream-error-boundary.fixture.ts
new file mode 100644
index 0000000000..02c7e6f07e
--- /dev/null
+++ b/tests/fixtures/adapta-web-stream-error-boundary.fixture.ts
@@ -0,0 +1,69 @@
+import assert from "node:assert/strict";
+import test from "node:test";
+
+assert.ok(process.env.DATA_DIR, "the subprocess fixture requires an isolated DATA_DIR");
+assert.ok(
+  process.env.OMNIROUTE_PLUGINS_DIR,
+  "the subprocess fixture requires an isolated OMNIROUTE_PLUGINS_DIR"
+);
+assert.equal(process.env.HOME, undefined, "the subprocess must not inherit HOME");
+assert.equal(process.env.CODEX_HOME, undefined, "the subprocess must not inherit CODEX_HOME");
+
+const { AdaptaWebExecutor } = await import("../../open-sse/executors/adapta-web.ts");
+
+const originalFetch = globalThis.fetch;
+
+test.afterEach(() => {
+  globalThis.fetch = originalFetch;
+});
+
+test("terminates an upstream error event without exposing its text in the public SSE", async () => {
+  const hostileError =
+    "SQLSTATE 42P01 at /srv/omniroute/private.ts:91 — Authorization: Bearer secret-token";
+  const requestedUrls: string[] = [];
+  const logMessages: string[] = [];
+
+  globalThis.fetch = (async (input: RequestInfo | URL) => {
+    const url = String(input);
+    requestedUrls.push(url);
+
+    if (url.endsWith("/v1/client")) {
+      return Response.json({
+        response: { sessions: [{ id: "session-stream-error", status: "active" }] },
+      });
+    }
+
+    if (url.includes("/tokens")) {
+      return Response.json({ jwt: "eyJ.test-session.jwt" });
+    }
+
+    return new Response(`data: ${JSON.stringify({ type: "error", errorText: hostileError })}\n\n`, {
+      status: 200,
+      headers: { "Content-Type": "text/event-stream" },
+    });
+  }) as typeof fetch;
+
+  const executor = new AdaptaWebExecutor();
+  const result = await executor.execute({
+    model: "adapta-one",
+    body: { messages: [{ role: "user", content: "hello" }] },
+    stream: true,
+    credentials: { apiKey: "__client=unique-stream-error-cookie" },
+    signal: null,
+    log: {
+      info: (_tag, message) => logMessages.push(message),
+      warn: (_tag, message) => logMessages.push(message),
+    },
+  });
+
+  assert.equal(result.response.status, 200);
+  assert.equal(result.response.headers.get("content-type"), "text/event-stream");
+
+  const publicSse = await result.response.text();
+  assert.equal(requestedUrls.length, 3);
+  assert.match(publicSse, /"content":"\\n\\n\[Erro: Adapta upstream error\]"/);
+  assert.match(publicSse, /"finish_reason":"stop"/);
+  assert.match(publicSse, /data: \[DONE\]/);
+  assert.doesNotMatch(publicSse, /SQLSTATE|\/srv\/omniroute|secret-token/);
+  assert.doesNotMatch(logMessages.join("\n"), /SQLSTATE|\/srv\/omniroute|secret-token/);
+});
diff --git a/tests/unit/executor-adapta-web-stream-error.test.ts b/tests/unit/executor-adapta-web-stream-error.test.ts
index 23cec6c610..f17667b92a 100644
--- a/tests/unit/executor-adapta-web-stream-error.test.ts
+++ b/tests/unit/executor-adapta-web-stream-error.test.ts
@@ -1,70 +1,97 @@
 import assert from "node:assert/strict";
-import { mkdirSync, mkdtempSync } from "node:fs";
-import { tmpdir } from "node:os";
-import { join } from "node:path";
+import { spawn } from "node:child_process";
+import fs from "node:fs";
+import os from "node:os";
+import path from "node:path";
+import { fileURLToPath } from "node:url";
 import test from "node:test";
 
-const testRoot = mkdtempSync(join(tmpdir(), "omniroute-adapta-stream-error-"));
-process.env.DATA_DIR = join(testRoot, "data");
-process.env.OMNIROUTE_PLUGINS_DIR = join(testRoot, "plugins");
-mkdirSync(process.env.DATA_DIR, { recursive: true });
-mkdirSync(process.env.OMNIROUTE_PLUGINS_DIR, { recursive: true });
+const FIXTURE = fileURLToPath(
+  new URL("../fixtures/adapta-web-stream-error-boundary.fixture.ts", import.meta.url)
+);
+const REPO_ROOT = fileURLToPath(new URL("../..", import.meta.url));
+const SYNTHETIC_API_KEY_SECRET =
+  "adapta-stream-boundary-test-secret-00000000000000000000000000000000";
 
-const { AdaptaWebExecutor } = await import("../../open-sse/executors/adapta-web.ts");
+type FixtureResult = {
+  code: number | null;
+  signal: NodeJS.Signals | null;
+  stdout: string;
+  stderr: string;
+};
 
-const originalFetch = globalThis.fetch;
+function runIsolatedFixture(testRoot: string): Promise<FixtureResult> {
+  const dataDir = path.join(testRoot, "data");
+  const pluginsDir = path.join(testRoot, "plugins");
+  fs.mkdirSync(dataDir, { recursive: true });
+  fs.mkdirSync(pluginsDir, { recursive: true });
 
-test.afterEach(() => {
-  globalThis.fetch = originalFetch;
-});
+  const childEnv: NodeJS.ProcessEnv = {
+    PATH: process.env.PATH,
+    NODE_PATH: process.env.NODE_PATH,
+    LANG: process.env.LANG ?? "C.UTF-8",
+    LC_ALL: process.env.LC_ALL,
+    TZ: process.env.TZ ?? "UTC",
+    TMPDIR: process.env.TMPDIR ?? os.tmpdir(),
+    NODE_ENV: "test",
+    APP_LOG_TO_FILE: "false",
+    API_KEY_SECRET: SYNTHETIC_API_KEY_SECRET,
+    DATA_DIR: dataDir,
+    OMNIROUTE_PLUGINS_DIR: pluginsDir,
+  };
+  delete childEnv.NODE_TEST_CONTEXT;
 
-test("terminates an upstream error event without exposing its text in the public SSE", async () => {
-  const hostileError =
-    "SQLSTATE 42P01 at /srv/omniroute/private.ts:91 — Authorization: Bearer secret-token";
-  const requestedUrls: string[] = [];
-  const logMessages: string[] = [];
-
-  globalThis.fetch = (async (input: RequestInfo | URL) => {
-    const url = String(input);
-    requestedUrls.push(url);
-
-    if (url.endsWith("/v1/client")) {
-      return Response.json({
-        response: { sessions: [{ id: "session-stream-error", status: "active" }] },
-      });
-    }
-
-    if (url.includes("/tokens")) {
-      return Response.json({ jwt: "eyJ.test-session.jwt" });
-    }
-
-    return new Response(`data: ${JSON.stringify({ type: "error", errorText: hostileError })}\n\n`, {
-      status: 200,
-      headers: { "Content-Type": "text/event-stream" },
+  return new Promise((resolve, reject) => {
+    const child = spawn(process.execPath, ["--import", "tsx/esm", "--test", FIXTURE], {
+      cwd: REPO_ROOT,
+      env: childEnv,
+      stdio: ["ignore", "pipe", "pipe"],
+      timeout: 90_000,
     });
-  }) as typeof fetch;
-
-  const executor = new AdaptaWebExecutor();
-  const result = await executor.execute({
-    model: "adapta-one",
-    body: { messages: [{ role: "user", content: "hello" }] },
-    stream: true,
-    credentials: { apiKey: "__client=unique-stream-error-cookie" },
-    signal: null,
-    log: {
-      info: (_tag, message) => logMessages.push(message),
-      warn: (_tag, message) => logMessages.push(message),
-    },
+    let stdout = "";
+    let stderr = "";
+    child.stdout.setEncoding("utf8").on("data", (chunk: string) => {
+      stdout += chunk;
+    });
+    child.stderr.setEncoding("utf8").on("data", (chunk: string) => {
+      stderr += chunk;
+    });
+    child.once("error", reject);
+    child.once("close", (code, signal) => resolve({ code, signal, stdout, stderr }));
   });
+}
 
-  assert.equal(result.response.status, 200);
-  assert.equal(result.response.headers.get("content-type"), "text/event-stream");
+test("Adapta stream errors are sanitized in an isolated executor fixture", async () => {
+  const testRoot = fs.mkdtempSync(path.join(os.tmpdir(), "omniroute-adapta-boundary-parent-"));
+  const originalDataDir = process.env.DATA_DIR;
+  const originalPluginsDir = process.env.OMNIROUTE_PLUGINS_DIR;
+  const originalFetch = globalThis.fetch;
+  const eventBusOwner = globalThis as { __omnirouteEventBus?: unknown };
+  const originalEventBus = eventBusOwner.__omnirouteEventBus;
 
-  const publicSse = await result.response.text();
-  assert.equal(requestedUrls.length, 3);
-  assert.match(publicSse, /"content":"\\n\\n\[Erro: Adapta upstream error\]"/);
-  assert.match(publicSse, /"finish_reason":"stop"/);
-  assert.match(publicSse, /data: \[DONE\]/);
-  assert.doesNotMatch(publicSse, /SQLSTATE|\/srv\/omniroute|secret-token/);
-  assert.doesNotMatch(logMessages.join("\n"), /SQLSTATE|\/srv\/omniroute|secret-token/);
+  try {
+    const result = await runIsolatedFixture(testRoot);
+    assert.equal(
+      result.code,
+      0,
+      `isolated Adapta fixture failed (signal=${result.signal ?? "none"})\n` +
+        `stdout:\n${result.stdout}\nstderr:\n${result.stderr}`
+    );
+    assert.equal(result.signal, null);
+    assert.match(result.stdout, /ℹ tests 1/);
+    assert.match(result.stdout, /ℹ pass 1/);
+    assert.match(result.stdout, /ℹ fail 0/);
+    assert.doesNotMatch(result.stdout + result.stderr, new RegExp(SYNTHETIC_API_KEY_SECRET));
+
+    assert.equal(process.env.DATA_DIR, originalDataDir);
+    assert.equal(process.env.OMNIROUTE_PLUGINS_DIR, originalPluginsDir);
+    assert.equal(globalThis.fetch, originalFetch);
+    assert.equal(
+      eventBusOwner.__omnirouteEventBus,
+      originalEventBus,
+      "the subprocess fixture must not replace the parent event bus singleton"
+    );
+  } finally {
+    fs.rmSync(testRoot, { recursive: true, force: true, maxRetries: 5, retryDelay: 100 });
+  }
 });