diff --git a/plugins/provider-codex/src/bridge/app-server-connection.line-separator.test.ts b/plugins/provider-codex/src/bridge/app-server-connection.line-separator.test.ts
new file mode 100644
index 0000000000..ed3a00ebc4
--- /dev/null
+++ b/plugins/provider-codex/src/bridge/app-server-connection.line-separator.test.ts
@@ -0,0 +1,45 @@
+import { expect, it } from "vitest";
+import { z } from "zod";
+
+import { createCodexAppServerConnection } from "./app-server-connection.js";
+
+// Echoes every request as a result whose string contains a raw U+2028.
+const FAKE_SERVER = `
+  process.stdin.setEncoding("utf8");
+  let buffered = "";
+  process.stdin.on("data", (chunk) => {
+    buffered += chunk;
+    let index;
+    while ((index = buffered.indexOf("\\n")) !== -1) {
+      const line = buffered.slice(0, index);
+      buffered = buffered.slice(index + 1);
+      const { id } = JSON.parse(line);
+      const text = "before\\u2028after";
+      process.stdout.write(JSON.stringify({ id, result: { text } }) + "\\n");
+    }
+  });
+`;
+
+it("keeps a JSON line intact when it contains U+2028", async () => {
+  const connection = createCodexAppServerConnection({
+    command: process.execPath,
+    args: ["-e", FAKE_SERVER],
+    cwd: process.cwd(),
+    env: process.env,
+    recordThreadId: null,
+    onNotification: () => {},
+    onRequest: () => {},
+    onExit: () => {},
+  });
+  try {
+    const result = await connection.request({
+      method: "thread/resume",
+      params: {},
+      resultSchema: z.object({ text: z.string() }),
+      timeoutMs: 5_000,
+    });
+    expect(result.text).toBe("before\u2028after");
+  } finally {
+    connection.kill();
+  }
+});
diff --git a/plugins/provider-codex/src/bridge/app-server-connection.ts b/plugins/provider-codex/src/bridge/app-server-connection.ts
index d055b8e54e..eb8081da3a 100644
--- a/plugins/provider-codex/src/bridge/app-server-connection.ts
+++ b/plugins/provider-codex/src/bridge/app-server-connection.ts
@@ -1,5 +1,6 @@
 import { spawn, type ChildProcess } from "node:child_process";
-import { createInterface, type Interface } from "node:readline";
+import { createInterface } from "node:readline";
+import { StringDecoder } from "node:string_decoder";
 import { experimental_recordProviderChildIo } from "@get-bb/plugin-sdk/provider-bridge";
 import type { z } from "zod";
 
@@ -111,7 +112,7 @@ export function createCodexAppServerConnection(
     signal: NodeJS.Signals | null;
   } | null = null;
   let closeGraceTimer: NodeJS.Timeout | null = null;
-  let stdoutLines: Interface | null = null;
+  let stdoutLines: { close(): void } | null = null;
 
   function writeLine(message: object): void {
     const stdin = child.stdin;
@@ -159,8 +160,15 @@ export function createCodexAppServerConnection(
   }
 
   if (child.stdout) {
-    stdoutLines = createInterface({ input: child.stdout, terminal: false });
-    stdoutLines.on("line", (line) => {
+    // Split strictly on "\n". `node:readline` also treats U+2028 and U+2029 as
+    // line breaks, which codex may emit unescaped inside JSON strings. That
+    // fragmented large responses (for example `thread/resume` for a thread whose
+    // history contained U+2028) into unparseable pieces, so the request never
+    // resolved and timed out.
+    const stdout = child.stdout;
+    const decoder = new StringDecoder("utf8");
+    let buffered = "";
+    const handleStdoutLine = (line: string) => {
       if (finalized) {
         return;
       }
@@ -222,7 +230,23 @@ export function createCodexAppServerConnection(
       }
 
       options.onNotification(message.method, message.params);
-    });
+    };
+    const onStdoutData = (chunk: Buffer) => {
+      buffered += decoder.write(chunk);
+      let newlineIndex = buffered.indexOf("\n");
+      while (newlineIndex !== -1) {
+        const line = buffered.slice(0, newlineIndex);
+        buffered = buffered.slice(newlineIndex + 1);
+        handleStdoutLine(line.endsWith("\r") ? line.slice(0, -1) : line);
+        newlineIndex = buffered.indexOf("\n");
+      }
+    };
+    stdout.on("data", onStdoutData);
+    stdoutLines = {
+      close() {
+        stdout.off("data", onStdoutData);
+      },
+    };
   }
 
   if (child.stderr) {