diff --git a/packages/server/src/server/agent/providers/codex-compaction-interrupt.local.e2e.test.ts b/packages/server/src/server/agent/providers/codex-compaction-interrupt.local.e2e.test.ts
new file mode 100644
index 0000000000..41928888ad
--- /dev/null
+++ b/packages/server/src/server/agent/providers/codex-compaction-interrupt.local.e2e.test.ts
@@ -0,0 +1,248 @@
+import { describe, expect, test, vi } from "vitest";
+import { execFileSync } from "node:child_process";
+import os from "node:os";
+import path from "node:path";
+import { createServer, type ServerResponse } from "node:http";
+import { mkdtempSync, rmSync, writeFileSync } from "node:fs";
+import { once } from "node:events";
+
+import { AgentManager } from "../agent-manager.js";
+import { AgentStorage } from "../agent-storage.js";
+import { sendPromptToAgent } from "../agent-prompt.js";
+import { CodexAppServerAgentClient } from "./codex-app-server-agent.js";
+import { createTestLogger } from "../../../test-utils/test-logger.js";
+
+function isCodexInstalled(): boolean {
+  try {
+    return (
+      execFileSync("which", ["codex"], { encoding: "utf8" }).trim().length > 0
+    );
+  } catch {
+    return false;
+  }
+}
+
+function sse(events: Array<Record<string, unknown>>): string {
+  return events
+    .map(
+      (event) =>
+        `event: ${String(event.type)}\ndata: ${JSON.stringify(event)}\n\n`
+    )
+    .join("");
+}
+
+function assistantSse(id: string, text: string, totalTokens: number): string {
+  return sse([
+    { type: "response.created", response: { id } },
+    {
+      type: "response.output_item.done",
+      item: {
+        type: "message",
+        role: "assistant",
+        id: `msg-${id}`,
+        content: [{ type: "output_text", text }],
+      },
+    },
+    {
+      type: "response.completed",
+      response: {
+        id,
+        usage: {
+          input_tokens: totalTokens,
+          input_tokens_details: null,
+          output_tokens: 0,
+          output_tokens_details: null,
+          total_tokens: totalTokens,
+        },
+      },
+    },
+  ]);
+}
+
+function isCompactionRequest(body: string): boolean {
+  return body.includes("CONTEXT CHECKPOINT COMPACTION");
+}
+
+async function startServer() {
+  const requests: Array<{ compaction: boolean; body: string }> = [];
+  const heldCompactions: ServerResponse[] = [];
+  let index = 0;
+  const server = createServer((req, res) => {
+    const chunks: Buffer[] = [];
+    req.on("data", (chunk) => chunks.push(Buffer.from(chunk)));
+    req.on("end", () => {
+      const body = Buffer.concat(chunks).toString("utf8");
+      if (req.method !== "POST" || req.url !== "/v1/responses") {
+        res.statusCode = 404;
+        res.end();
+        return;
+      }
+      const compaction = isCompactionRequest(body);
+      requests.push({ compaction, body });
+      res.statusCode = 200;
+      res.setHeader("content-type", "text/event-stream");
+      if (compaction) {
+        // Hold the summarization open, as a slow real compaction would be.
+        heldCompactions.push(res);
+        return;
+      }
+      index += 1;
+      // The first turn reports a context far above the auto-compact limit.
+      res.end(
+        assistantSse(
+          `resp-${index}`,
+          `reply ${index}`,
+          index === 1 ? 50_000 : 100
+        )
+      );
+    });
+  });
+  server.listen(0, "127.0.0.1");
+  await once(server, "listening");
+  const address = server.address();
+  if (!address || typeof address === "string") throw new Error("no address");
+  return {
+    url: `http://127.0.0.1:${address.port}`,
+    requests,
+    releaseCompactions() {
+      for (const res of heldCompactions.splice(0)) {
+        res.end(assistantSse("summary", "SUMMARY", 100));
+      }
+    },
+    close: () =>
+      new Promise<void>((resolve) => {
+        for (const res of heldCompactions.splice(0)) res.destroy();
+        server.closeAllConnections();
+        server.close(() => resolve());
+      }),
+  };
+}
+
+function writeConfig(codexHome: string, serverUrl: string): void {
+  writeFileSync(
+    path.join(codexHome, "config.toml"),
+    `
+model = "mock-model"
+approval_policy = "on-request"
+sandbox_mode = "read-only"
+model_provider = "mock_provider"
+model_auto_compact_token_limit = 10000
+
+[model_providers.mock_provider]
+name = "Mock provider for test"
+base_url = "${serverUrl}/v1"
+wire_api = "responses"
+request_max_retries = 0
+stream_max_retries = 0
+`
+  );
+}
+
+async function waitFor(
+  check: () => boolean,
+  label: string,
+  timeoutMs = 15_000
+): Promise<void> {
+  const deadline = Date.now() + timeoutMs;
+  while (!check()) {
+    if (Date.now() > deadline)
+      throw new Error(`Timed out waiting for ${label}`);
+    await new Promise((resolve) => setTimeout(resolve, 50));
+  }
+}
+
+describe("Codex compaction and incoming prompts (local e2e)", () => {
+  for (const behavior of ["send_agent_prompt default", "steer"] as const) {
+    test.runIf(isCodexInstalled())(
+      `${behavior}: messages from other agents during auto-compaction do not restart it (#5728)`,
+      async () => {
+        const cwd = mkdtempSync(path.join(os.tmpdir(), "codex-compact-cwd-"));
+        const codexHome = mkdtempSync(
+          path.join(os.tmpdir(), "codex-compact-home-")
+        );
+        const server = await startServer();
+        const logger = createTestLogger();
+        const storage = new AgentStorage(path.join(cwd, "agents"), logger);
+        const manager = new AgentManager({
+          clients: { codex: new CodexAppServerAgentClient(logger) },
+          registry: storage,
+          logger,
+        });
+        let agentId: string | undefined;
+        try {
+          writeConfig(codexHome, server.url);
+          vi.stubEnv("CODEX_HOME", codexHome);
+          const created = await manager.createAgent(
+            { provider: "codex", cwd, modeId: "auto", model: "mock-model" },
+            undefined,
+            { workspaceId: undefined }
+          );
+          agentId = created.id;
+          const id = agentId;
+          await manager.runAgent(id, "first turn");
+
+          const send = (text: string) =>
+            sendPromptToAgent({
+              agentManager: manager,
+              agentStorage: storage,
+              agentId: id,
+              prompt: text,
+              ...(behavior === "steer"
+                ? { activeTurnBehavior: "steer" as const }
+                : {}),
+              logger,
+            });
+          const compactions = () =>
+            server.requests.filter((r) => r.compaction).length;
+
+          await send("second turn");
+          await waitFor(() => compactions() === 1, "first compaction request");
+
+          // Two more messages arrive from other agents while it compacts.
+          await send("update from agent A");
+          await new Promise((resolve) => setTimeout(resolve, 1500));
+          await send("update from agent B");
+          await new Promise((resolve) => setTimeout(resolve, 1500));
+
+          // Each message that replaced the turn aborted the compaction and started another.
+          expect(compactions()).toBe(1);
+          server.releaseCompactions();
+          await waitFor(
+            () => manager.getAgent(id)?.lifecycle === "idle",
+            "agent idle",
+            20_000
+          );
+
+          // Every message reaches Codex and the chat, once compaction finishes.
+          const delivered = server.requests
+            .filter((request) => !request.compaction)
+            .map((request) => request.body)
+            .join("\n");
+          const chat = manager
+            .getTimeline(id)
+            .flatMap((item) =>
+              item.type === "user_message" ? [item.text] : []
+            );
+          for (const text of [
+            "second turn",
+            "update from agent A",
+            "update from agent B",
+          ]) {
+            expect(delivered).toContain(text);
+            expect(chat).toContain(text);
+          }
+          expect(compactions()).toBe(1);
+        } finally {
+          if (agentId && manager.getAgent(agentId))
+            await manager.closeAgent(agentId);
+          await storage.flush();
+          vi.unstubAllEnvs();
+          await server.close();
+          rmSync(cwd, { recursive: true, force: true });
+          rmSync(codexHome, { recursive: true, force: true });
+        }
+      },
+      60_000
+    );
+  }
+});