diff --git a/scripts/test-layout/layout-codex-collision.json b/scripts/test-layout/layout-codex-collision.json
index d9af6341408..8bb668619f0 100644
--- a/scripts/test-layout/layout-codex-collision.json
+++ b/scripts/test-layout/layout-codex-collision.json
@@ -31,6 +31,7 @@
   "codex-launcher-env.test.ts": "codex-integration",
   "codex-cli-update-artifacts.test.ts": "codex-integration",
   "codex-cli-update-apply.test.ts": "codex-integration",
+  "codex-cli-update-process-fixture.test.ts": "codex-integration",
   "codex-cli-update-paths.test.ts": "codex-integration",
   "codex-cli-update-admission.test.ts": "codex-integration",
   "codex-cli-update-recovery.test.ts": "codex-integration",
diff --git a/tests/codex-integration/codex-cli-update-apply.test.ts b/tests/codex-integration/codex-cli-update-apply.test.ts
index dea2f9b1fb9..687a8a47f3e 100644
--- a/tests/codex-integration/codex-cli-update-apply.test.ts
+++ b/tests/codex-integration/codex-cli-update-apply.test.ts
@@ -43,7 +43,7 @@ async function approved(f: ReturnType<typeof fixture>, deps = depsFor(f)) {
 }
 function cli(f: ReturnType<typeof fixture>, args: string[]) {
   const result = spawnSync(Bun.which("node")!, [repoPath("bin", "ocx.mjs"), "system", "codex-cli-update", ...args, "--json"], {
-    cwd: repoRoot(), encoding: "utf8", env: f.env, timeout: 60_000,
+    cwd: f.root, encoding: "utf8", env: f.env, timeout: 60_000,
   });
   expect(result.error).toBeUndefined(); expect(result.status).toBe(0);
   return JSON.parse(result.stdout);
@@ -373,6 +373,14 @@ describe.skipIf(!posix)("Codex CLI private-prefix POSIX apply", () => {
     try {
       await waitForManagementServer(base, server.child, server.closed, server.output);
       session = await issueFixtureGuiSession(base);
+      for (const [scan, refusal] of [["active", "blocked_active_session"], ["unavailable", "blocked_process_state_unknown"]] as const) {
+        writeFileSync(join(f.root, "process-scan-state.json"), JSON.stringify({ scans: [scan] }));
+        const response = await fetch(`${base}/api/codex/cli-update/plan`, { headers: fixtureSessionHeaders(session) });
+        expect(response.ok).toBe(true);
+        expect(await response.json()).toMatchObject({ applicable: false, refusal });
+        expect(readFileSync(f.trace, "utf8")).toBe("");
+      }
+      writeFileSync(join(f.root, "process-scan-state.json"), JSON.stringify({ scans: ["empty", "empty", "empty"] }));
       const planResponse = await fetch(`${base}/api/codex/cli-update/plan`, { headers: fixtureSessionHeaders(session) });
       if (!planResponse.ok) throw new Error(`isolated production plan refused (${planResponse.status})`);
       const plan = await planResponse.json() as { schemaVersion?: number; applicable: boolean; refusal?: string | null;
diff --git a/tests/codex-integration/codex-cli-update-process-fixture.test.ts b/tests/codex-integration/codex-cli-update-process-fixture.test.ts
new file mode 100644
index 00000000000..1e43f48deb1
--- /dev/null
+++ b/tests/codex-integration/codex-cli-update-process-fixture.test.ts
@@ -0,0 +1,96 @@
+import { afterEach, describe, expect, test } from "bun:test";
+import { spawn, spawnSync } from "node:child_process";
+import { readFileSync, writeFileSync } from "node:fs";
+import { join } from "node:path";
+import { scanCodexSessionProcessesAsync } from "../../src/codex/app-server-processes";
+import { createCodexCliApplyFixture } from "../helpers/codex-cli-apply-fixture";
+import { createCodexCliTestRoot } from "../helpers/codex-cli-fixture-root";
+import { removeTreeWithRetry } from "../helpers/remove-tree";
+import { repoPath } from "../helpers/repo-root";
+
+const roots: string[] = [];
+afterEach(() => { for (const root of roots.splice(0)) removeTreeWithRetry(root); });
+function fixture() {
+  const root = createCodexCliTestRoot("ocx-apply-private-"); roots.push(root);
+  return createCodexCliApplyFixture(root, process.platform, process.arch);
+}
+function cli(f: ReturnType<typeof fixture>, args: string[], exitCode = 0) {
+  const result = spawnSync(Bun.which("node")!, [repoPath("bin", "ocx.mjs"), "system", "codex-cli-update", ...args, "--json"], {
+    cwd: f.root, encoding: "utf8", env: f.env, timeout: 60_000,
+  });
+  expect(result.error).toBeUndefined(); expect(result.status).toBe(exitCode);
+  return JSON.parse(result.stdout);
+}
+
+describe.skipIf(process.platform === "win32")("Codex CLI private-prefix POSIX apply", () => {
+  test.each([
+    ["active", JSON.stringify({ scans: ["active"] }), "blocked_active_session"],
+    ["unavailable", JSON.stringify({ scans: ["unavailable"] }), "blocked_process_state_unknown"],
+    ["malformed", "not-json", "blocked_process_state_unknown"],
+    ["exhausted", JSON.stringify({ scans: [] }), "blocked_process_state_unknown"],
+  ])("fixture scan %s keeps the real plan refusal", (_name, state, refusal) => {
+    const f = fixture();
+    writeFileSync(join(f.root, "process-scan-state.json"), state);
+    const plan = cli(f, ["plan"]);
+    expect(plan).toMatchObject({ applicable: false, refusal });
+    expect(readFileSync(f.trace, "utf8")).toBe("");
+  }, 120_000);
+
+  test.each([["active", "blocked_active_session"], ["unavailable", "blocked_process_state_unknown"]] as const)(
+    "fixture final scan %s refuses before installer admission", (last, refusal) => {
+      const f = fixture();
+      const plan = cli(f, ["plan"]);
+      expect(plan.applicable).toBe(true);
+      writeFileSync(join(f.root, "process-scan-state.json"), JSON.stringify({ scans: ["empty", "empty", last] }));
+      const result = cli(f, ["apply", "--plan-id", plan.planId, "--yes"], 1);
+      expect(result).toMatchObject({ outcome: "refused", reason: refusal });
+      const scans = readFileSync(join(f.root, "process-scan-trace.jsonl"), "utf8").trim().split("\n")
+        .map(line => JSON.parse(line) as { value: string; index: number });
+      expect(scans).toEqual([{ value: "empty", index: 1 }, { value: "empty", index: 1 },
+        { value: "empty", index: 2 }, { value: last, index: 3 }]);
+      expect(readFileSync(f.trace, "utf8")).toBe("");
+    }, 120_000);
+
+  test("published launcher remains isolated from a real owned Codex-shaped process", async () => {
+    const f = fixture();
+    const node = Bun.which("node");
+    if (!node) throw new Error("fixture node executable unavailable");
+    const entry = join(f.root, "codex");
+    writeFileSync(entry, 'process.stdout.write("READY\\n"); process.stdin.resume();\n');
+    const child = spawn(node, [entry], { cwd: f.root, env: f.env, stdio: ["pipe", "pipe", "pipe"] });
+    const closed = new Promise<{ code: number | null; signal: NodeJS.Signals | null }>(resolve => {
+      child.once("close", (code, signal) => resolve({ code, signal }));
+    });
+    try {
+      const ready = new Promise<string>((resolve, reject) => {
+        let output = "";
+        child.stdout!.on("data", chunk => {
+          output += String(chunk);
+          if (output.includes("\n")) resolve(output);
+        });
+        child.once("error", reject);
+        closed.then(() => reject(new Error("owned fixture process exited before READY")));
+      });
+      expect(await ready).toBe("READY\n");
+      const scan = await scanCodexSessionProcessesAsync();
+      expect(scan.kind).toBe("observed");
+      if (scan.kind !== "observed") throw new Error("native session scan unavailable");
+      expect(scan.processes.some(process => process.pid === child.pid)).toBe(true);
+      const bunfig = join(f.root, "bunfig.toml");
+      const fixtureConfig = readFileSync(bunfig, "utf8");
+      writeFileSync(bunfig, "");
+      expect(cli(f, ["plan"])).toMatchObject({ applicable: false, refusal: "blocked_active_session" });
+      writeFileSync(bunfig, fixtureConfig);
+      const plan = cli(f, ["plan"]);
+      expect(plan.applicable).toBe(true);
+      const result = cli(f, ["apply", "--plan-id", plan.planId, "--yes"]);
+      expect(result).toMatchObject({ status: "applied", outcome: "applied", childState: "terminal" });
+      expect(readFileSync(f.trace, "utf8").trim().split("\n")).toHaveLength(1);
+    } finally {
+      child.stdin?.end();
+      const exit = await closed;
+      expect(exit).toEqual({ code: 0, signal: null });
+    }
+  }, 120_000);
+
+});
diff --git a/tests/fixtures/test-layout-expected.json b/tests/fixtures/test-layout-expected.json
index 71a17ebfca7..80eb6eab44f 100644
--- a/tests/fixtures/test-layout-expected.json
+++ b/tests/fixtures/test-layout-expected.json
@@ -83,6 +83,7 @@
     "codex-cli-windows-child.test.ts": "codex-integration",
     "codex-cli-update-artifacts.test.ts": "codex-integration",
     "codex-cli-update-apply.test.ts": "codex-integration",
+    "codex-cli-update-process-fixture.test.ts": "codex-integration",
     "codex-cli-update-paths.test.ts": "codex-integration",
     "codex-cli-update-admission.test.ts": "codex-integration",
     "codex-cli-update-recovery.test.ts": "codex-integration",
diff --git a/tests/helpers/codex-cli-apply-fixture.ts b/tests/helpers/codex-cli-apply-fixture.ts
index 73371d5d17c..9d5406afe66 100644
--- a/tests/helpers/codex-cli-apply-fixture.ts
+++ b/tests/helpers/codex-cli-apply-fixture.ts
@@ -4,6 +4,7 @@ import { dirname, join } from "node:path";
 import { createNpmConfigIsolation, isolatedNpmTarget } from "../../src/codex/cli-update-plan";
 import { fixtureArtifact, fixtureArtifactSet } from "./codex-cli-apply-artifact";
 import type { CodexCliApplyResult } from "../../src/codex/cli-update-apply";
+import { helperPath } from "./repo-root";
 
 /** Admission waits must also observe an early refusal/rejection. Otherwise a
  * diagnostic failure before install/fetch entry becomes a misleading timeout.
@@ -100,6 +101,9 @@ export function createCodexCliApplyFixture(root: string, platform: NodeJS.Platfo
   ]));
   if (process.platform !== "win32") {
     writeFixtureNpmWrapper(fakeBin, node, realNpm, metadata, packs, trace);
+    // A private cwd makes this preload local to the published-launcher fixtures.
+    writeFileSync(join(root, "bunfig.toml"), `preload = [${JSON.stringify(helperPath("codex-cli-process-scan-preload.ts"))}]\n`);
+    writeFileSync(join(root, "process-scan-state.json"), JSON.stringify({ scans: ["empty", "empty", "empty"] }));
   }
   const launcher = process.platform === "win32" ? join(prefix, "codex.cmd") : join(prefix, "bin", "codex");
   const env = { ...process.env, HOME: home, TMPDIR: temporaryRoot, OPENCODEX_HOME: join(home, "ocx"),
diff --git a/tests/helpers/codex-cli-process-scan-preload.ts b/tests/helpers/codex-cli-process-scan-preload.ts
new file mode 100644
index 00000000000..d3bbdaf1fd6
--- /dev/null
+++ b/tests/helpers/codex-cli-process-scan-preload.ts
@@ -0,0 +1,40 @@
+import { mock } from "bun:test";
+import { appendFileSync, readFileSync } from "node:fs";
+import { join } from "node:path";
+import { fileURLToPath } from "node:url";
+
+// Only fixture-owned Bun processes load this file through their private bunfig.
+// Keep the published CLI and update worker real; replace only their process view.
+if (Bun.isMainThread) {
+  const workerModule = await import("../../src/lib/worker-embed");
+  const spawnOriginal = workerModule.spawnWorker;
+  mock.module(import.meta.resolve("../../src/lib/worker-embed"), () => ({
+    ...workerModule,
+    spawnWorker: (url: string, key: string) => key === "cli-update-worker"
+      ? new Worker(url, { preload: [fileURLToPath(import.meta.url)] })
+      : spawnOriginal(url, key),
+  }));
+} else {
+  const processModule = await import("../../src/codex/app-server-processes");
+  const scanOriginal = processModule.scanCodexSessionProcesses;
+  const scanAsyncOriginal = processModule.scanCodexSessionProcessesAsync;
+  let index = 0;
+  const snapshots = () => {
+    const state = JSON.parse(readFileSync(join(process.cwd(), "process-scan-state.json"), "utf8")) as { scans?: unknown };
+    if (!Array.isArray(state.scans) || !state.scans.every(value => ["empty", "active", "unavailable"].includes(value))) {
+      throw new Error("invalid fixture process scan state");
+    }
+    const value = state.scans[index++];
+    if (value === undefined) throw new Error("fixture process scan sequence exhausted");
+    appendFileSync(join(process.cwd(), "process-scan-trace.jsonl"), JSON.stringify({ value, index }) + "\n");
+    if (value === "unavailable") throw new Error("fixture process scan unavailable");
+    return value === "active" ? [{ pid: 918273, commandLine: "codex", executable: "codex" }] : [];
+  };
+  mock.module(import.meta.resolve("../../src/codex/app-server-processes"), () => ({
+    ...processModule,
+    scanCodexSessionProcesses: (io: Parameters<typeof scanOriginal>[0] = {}) =>
+      scanOriginal({ ...io, listSnapshots: snapshots }),
+    scanCodexSessionProcessesAsync: (io: Parameters<typeof scanAsyncOriginal>[0] = {}) =>
+      scanAsyncOriginal({ ...io, listSnapshotsAsync: async () => snapshots() }),
+  }));
+}