diff --git a/server/src/__tests__/agent-instructions-service.test.ts b/server/src/__tests__/agent-instructions-service.test.ts
index 52c2142ade3..a8b97e4713e 100644
--- a/server/src/__tests__/agent-instructions-service.test.ts
+++ b/server/src/__tests__/agent-instructions-service.test.ts
@@ -431,6 +431,33 @@ describe("agent instructions service", () => {
     await expect(fs.stat(path.join(updated.bundle.managedRootPath, "docs", "OLD.md"))).rejects.toThrow();
   });
 
+  it("serializes concurrent routine materializations for the same agent", async () => {
+    const paperclipHome = await makeTempDir("paperclip-agent-instructions-concurrent-");
+    cleanupDirs.add(paperclipHome);
+    process.env.PAPERCLIP_HOME = paperclipHome;
+    process.env.PAPERCLIP_INSTANCE_ID = "test-instance";
+    const svc = agentInstructionsService();
+    const agent = makeAgent({});
+    const initial = await svc.materializeManagedBundle(agent, { "AGENTS.md": "# Stock v1\n" });
+    const configuredAgent = { ...agent, adapterConfig: initial.adapterConfig };
+
+    const [first, second] = await Promise.all([
+      svc.materializeManagedBundle(configuredAgent, { "AGENTS.md": "# Stock v2\n" }),
+      agentInstructionsService().materializeManagedBundle(configuredAgent, {
+        "AGENTS.md": "# Stock v3\n",
+      }),
+    ]);
+
+    expect(first.materialization.action).toBe("updated");
+    expect(second.materialization).toMatchObject({
+      stockStatus: "operator_modified",
+      action: "skipped",
+    });
+    await expect(fs.readFile(path.join(initial.bundle.managedRootPath, "AGENTS.md"), "utf8")).resolves.toBe(
+      "# Stock v2\n",
+    );
+  });
+
   it("canonicalizes line endings and ignores transient files when classifying drift", async () => {
     const paperclipHome = await makeTempDir("paperclip-agent-instructions-canonical-");
     cleanupDirs.add(paperclipHome);
@@ -518,4 +545,34 @@ describe("agent instructions service", () => {
       "# Second operator edit\n",
     );
   });
+
+  it("allocates distinct backups for concurrent force resets", async () => {
+    const paperclipHome = await makeTempDir("paperclip-agent-instructions-concurrent-reset-");
+    cleanupDirs.add(paperclipHome);
+    process.env.PAPERCLIP_HOME = paperclipHome;
+    process.env.PAPERCLIP_INSTANCE_ID = "test-instance";
+    const svc = agentInstructionsService();
+    const agent = makeAgent({});
+    const initial = await svc.materializeManagedBundle(agent, { "AGENTS.md": "# Stock v1\n" });
+    const configuredAgent = { ...agent, adapterConfig: initial.adapterConfig };
+
+    const [first, second] = await Promise.all([
+      svc.forceResetManagedBundle(configuredAgent, { "AGENTS.md": "# Stock v2\n" }),
+      agentInstructionsService().forceResetManagedBundle(configuredAgent, {
+        "AGENTS.md": "# Stock v3\n",
+      }),
+    ]);
+
+    expect(first.materialization.backupPath).toBe(`${initial.bundle.managedRootPath}.backup-1`);
+    expect(second.materialization.backupPath).toBe(`${initial.bundle.managedRootPath}.backup-2`);
+    await expect(
+      fs.readFile(path.join(`${initial.bundle.managedRootPath}.backup-1`, "AGENTS.md"), "utf8"),
+    ).resolves.toBe("# Stock v1\n");
+    await expect(
+      fs.readFile(path.join(`${initial.bundle.managedRootPath}.backup-2`, "AGENTS.md"), "utf8"),
+    ).resolves.toBe("# Stock v2\n");
+    await expect(fs.readFile(path.join(initial.bundle.managedRootPath, "AGENTS.md"), "utf8")).resolves.toBe(
+      "# Stock v3\n",
+    );
+  });
 });
diff --git a/server/src/services/agent-instructions.ts b/server/src/services/agent-instructions.ts
index ae6964133b9..8b0d16a6f05 100644
--- a/server/src/services/agent-instructions.ts
+++ b/server/src/services/agent-instructions.ts
@@ -28,6 +28,7 @@ const IGNORED_INSTRUCTIONS_DIRECTORY_NAMES = new Set([
   "node_modules",
   "venv",
 ]);
+const managedBundleMaterializationTails = new Map<string, Promise<void>>();
 
 type BundleMode = "managed" | "external";
 
@@ -174,6 +175,29 @@ async function statIfExists(targetPath: string) {
   return fs.stat(targetPath).catch(() => null);
 }
 
+async function withManagedBundleMaterializationLock<T>(
+  rootPath: string,
+  operation: () => Promise<T>,
+): Promise<T> {
+  const previous = managedBundleMaterializationTails.get(rootPath) ?? Promise.resolve();
+  let release!: () => void;
+  const current = new Promise<void>((resolve) => {
+    release = resolve;
+  });
+  const tail = previous.catch(() => undefined).then(() => current);
+  managedBundleMaterializationTails.set(rootPath, tail);
+
+  await previous.catch(() => undefined);
+  try {
+    return await operation();
+  } finally {
+    release();
+    if (managedBundleMaterializationTails.get(rootPath) === tail) {
+      managedBundleMaterializationTails.delete(rootPath);
+    }
+  }
+}
+
 function shouldIgnoreInstructionsEntry(entry: { name: string; isDirectory(): boolean; isFile(): boolean }) {
   if (entry.name === "." || entry.name === "..") return true;
   if (entry.isDirectory()) {
@@ -937,7 +961,10 @@ export function agentInstructionsService() {
       recordedStockHash?: string | null;
     },
   ) {
-    return materializeManagedBundleInternal(agent, files, options);
+    const rootPath = resolveManagedInstructionsRoot(agent);
+    return withManagedBundleMaterializationLock(rootPath, () =>
+      materializeManagedBundleInternal(agent, files, options),
+    );
   }
 
   async function forceResetManagedBundle(
@@ -949,7 +976,10 @@ export function agentInstructionsService() {
       recordedStockHash?: string | null;
     },
   ) {
-    return materializeManagedBundleInternal(agent, files, { ...options, forceReset: true });
+    const rootPath = resolveManagedInstructionsRoot(agent);
+    return withManagedBundleMaterializationLock(rootPath, () =>
+      materializeManagedBundleInternal(agent, files, { ...options, forceReset: true }),
+    );
   }
 
   return {