diff --git a/src/code-mode.ts b/src/code-mode.ts
index f3447c5e..0bd217dc 100644
--- a/src/code-mode.ts
+++ b/src/code-mode.ts
@@ -29,6 +29,20 @@ async function writeCodeModeWorkflow(
     "openwiki-update.yml",
   );
   await mkdir(path.dirname(workflowPath), { recursive: true });
+
+  // Only create the workflow if it doesn't already exist — respect any
+  // customizations the user has made (cron schedule, env vars, fork guards, etc.).
+  try {
+    await readFile(workflowPath, "utf8");
+    // File exists: leave it untouched so user edits survive.
+    return;
+  } catch (error) {
+    if (!isFileNotFoundError(error)) {
+      throw error;
+    }
+    // File not found: fall through to create it.
+  }
+
   await writeFile(workflowPath, createCodeModeWorkflow(cronExpression), "utf8");
 }
 
diff --git a/src/constants.ts b/src/constants.ts
index 1c1eb2bb..74b26bc3 100644
--- a/src/constants.ts
+++ b/src/constants.ts
@@ -375,7 +375,7 @@ export function isValidModelId(value: string): boolean {
   return (
     modelId.length > 0 &&
     modelId.length <= 120 &&
-    /^[A-Za-z0-9][A-Za-z0-9._:/+-]*$/u.test(modelId) &&
+    /^[@A-Za-z0-9][A-Za-z0-9._:/+-]*$/u.test(modelId) &&
     !modelId.includes("://")
   );
 }
diff --git a/test/code-mode.test.ts b/test/code-mode.test.ts
index 11df0650..771b0c46 100644
--- a/test/code-mode.test.ts
+++ b/test/code-mode.test.ts
@@ -1,4 +1,4 @@
-import { mkdtemp, readFile, rm, writeFile } from "node:fs/promises";
+import { mkdir, mkdtemp, readFile, rm, writeFile } from "node:fs/promises";
 import { tmpdir } from "node:os";
 import path from "node:path";
 import { afterEach, describe, expect, test } from "vitest";
@@ -100,7 +100,7 @@ Trailing notes that must survive.
 });
 
 describe("ensureCodeModeRepoSetup workflow", () => {
-  test("generated PR includes agent files and the workflow in add-paths", async () => {
+  test("creates workflow when it does not exist", async () => {
     const repo = await createTempRepo();
 
     await ensureCodeModeRepoSetup(repo);
@@ -119,4 +119,71 @@ describe("ensureCodeModeRepoSetup workflow", () => {
       expect(workflow).toContain(managedPath);
     }
   });
+
+  test("preserves existing customized workflow and does not overwrite", async () => {
+    const repo = await createTempRepo();
+    const customWorkflow = `name: OpenWiki Update
+
+on:
+  workflow_dispatch:
+  schedule:
+    - cron: "0 2 * * 1"
+
+permissions:
+  contents: write
+  pull-requests: write
+
+jobs:
+  update:
+    if: github.repository == 'my-org/my-repo'
+    runs-on: ubuntu-latest
+    steps:
+      - name: Check out repository
+        uses: actions/checkout@v4
+        with:
+          persist-credentials: true
+
+      - name: Run OpenWiki
+        run: openwiki code --update --print
+        env:
+          OPENWIKI_PROVIDER: anthropic
+          ANTHROPIC_API_KEY: \${{ secrets.ANTHROPIC_API_KEY }}
+          OPENWIKI_MODEL_ID: claude-sonnet-4-20250514
+`;
+    const workflowDir = path.join(repo, ".github", "workflows");
+    await mkdir(workflowDir, { recursive: true });
+    await writeFile(
+      path.join(workflowDir, "openwiki-update.yml"),
+      customWorkflow,
+      "utf8",
+    );
+
+    await ensureCodeModeRepoSetup(repo);
+
+    const workflow = await readIfPresent(
+      path.join(workflowDir, "openwiki-update.yml"),
+    );
+    // Must preserve the user's customizations, not overwrite with defaults.
+    expect(workflow).toBe(customWorkflow);
+    expect(workflow).toContain('cron: "0 2 * * 1"');
+    expect(workflow).toContain("if: github.repository == 'my-org/my-repo'");
+    expect(workflow).toContain("OPENWIKI_PROVIDER: anthropic");
+    expect(workflow).toContain("claude-sonnet-4-20250514");
+    expect(workflow).toContain("persist-credentials: true");
+  });
+
+  test("is idempotent across repeated runs for workflow", async () => {
+    const repo = await createTempRepo();
+
+    await ensureCodeModeRepoSetup(repo);
+    const first = await readIfPresent(
+      path.join(repo, ".github", "workflows", "openwiki-update.yml"),
+    );
+    await ensureCodeModeRepoSetup(repo);
+    const second = await readIfPresent(
+      path.join(repo, ".github", "workflows", "openwiki-update.yml"),
+    );
+
+    expect(second).toEqual(first);
+  });
 });
diff --git a/test/constants.test.ts b/test/constants.test.ts
index bbcae399..2fdf5698 100644
--- a/test/constants.test.ts
+++ b/test/constants.test.ts
@@ -24,6 +24,12 @@ describe("isValidModelId", () => {
     expect(isValidModelId("nvidia/nemotron-3-super-120b-a12b")).toBe(true);
   });
 
+  test("accepts Cloudflare Workers AI model ids with leading '@'", () => {
+    expect(isValidModelId("@cf/meta/llama-3-8b-instruct")).toBe(true);
+    expect(isValidModelId("@cf/moonshotai/kimi-k2.7-code")).toBe(true);
+    expect(isValidModelId("@cf/qwen/qwen1.5-14b-chat-awq")).toBe(true);
+  });
+
   test("rejects empty, whitespace-only, and over-long ids", () => {
     expect(isValidModelId("")).toBe(false);
     expect(isValidModelId("   ")).toBe(false);