diff --git a/src/cli/gateway-cli/dev.integration.test.ts b/src/cli/gateway-cli/dev.integration.test.ts
new file mode 100644
index 000000000000..ad21300f03a2
--- /dev/null
+++ b/src/cli/gateway-cli/dev.integration.test.ts
@@ -0,0 +1,44 @@
+// Proves a fresh dev gateway can replace the synthetic implicit roster through real config IO.
+import { mkdtemp, readFile, rm } from "node:fs/promises";
+import os from "node:os";
+import path from "node:path";
+import { afterEach, describe, expect, it } from "vitest";
+import { resetConfigRuntimeState } from "../../config/config.js";
+import { withEnvAsync } from "../../test-utils/env.js";
+import { ensureDevGatewayConfig } from "./dev.js";
+
+describe("ensureDevGatewayConfig integration", () => {
+  const tempDirs: string[] = [];
+
+  afterEach(async () => {
+    resetConfigRuntimeState();
+    await Promise.all(tempDirs.splice(0).map((dir) => rm(dir, { recursive: true, force: true })));
+  });
+
+  it("writes the dedicated dev roster into a fresh state directory", async () => {
+    const root = await mkdtemp(path.join(os.tmpdir(), "openclaw-dev-config-integration-"));
+    tempDirs.push(root);
+    const stateDir = path.join(root, "state");
+    const configPath = path.join(stateDir, "openclaw.json");
+    const workspace = path.join(root, "workspace");
+
+    await withEnvAsync(
+      {
+        OPENCLAW_CONFIG_PATH: configPath,
+        OPENCLAW_STATE_DIR: stateDir,
+        OPENCLAW_WORKSPACE_DIR: workspace,
+      },
+      async () => {
+        resetConfigRuntimeState();
+        await ensureDevGatewayConfig({});
+      },
+    );
+
+    const config = JSON.parse(await readFile(configPath, "utf8")) as {
+      agents?: { entries?: Record<string, { default?: boolean; workspace?: string }> };
+    };
+    expect(config.agents?.entries).toEqual({
+      dev: { default: true, workspace: `${workspace}-dev`, identity: expect.any(Object) },
+    });
+  });
+});
diff --git a/src/cli/gateway-cli/dev.test.ts b/src/cli/gateway-cli/dev.test.ts
index 3e22c71703f9..c20caa2a873d 100644
--- a/src/cli/gateway-cli/dev.test.ts
+++ b/src/cli/gateway-cli/dev.test.ts
@@ -9,6 +9,7 @@ const mocks = vi.hoisted(() => ({
   configPath: "",
   workspace: "",
   nextConfig: undefined as unknown,
+  writeOptions: undefined as unknown,
   replaceConfigFile: vi.fn(),
 }));
 
@@ -48,9 +49,12 @@ describe("ensureDevGatewayConfig", () => {
     mocks.configPath = path.join(tempDir, "openclaw.json");
     mocks.workspace = path.join(tempDir, "workspace");
     mocks.nextConfig = undefined;
+    mocks.writeOptions = undefined;
     mocks.replaceConfigFile.mockReset();
     mocks.replaceConfigFile.mockImplementation(async (options: unknown) => {
-      mocks.nextConfig = (options as { nextConfig: unknown }).nextConfig;
+      const configOptions = options as { nextConfig: unknown; writeOptions?: unknown };
+      mocks.nextConfig = configOptions.nextConfig;
+      mocks.writeOptions = configOptions.writeOptions;
     });
   });
 
@@ -76,5 +80,6 @@ describe("ensureDevGatewayConfig", () => {
       },
     });
     expect(OpenClawSchema.safeParse(mocks.nextConfig).success).toBe(true);
+    expect(mocks.writeOptions).toEqual({ allowedAgentRosterRemovals: ["main"] });
   });
 });
diff --git a/src/cli/gateway-cli/dev.ts b/src/cli/gateway-cli/dev.ts
index db7e970f5f8f..8751217a1668 100644
--- a/src/cli/gateway-cli/dev.ts
+++ b/src/cli/gateway-cli/dev.ts
@@ -8,6 +8,7 @@ import { resolveWorkspaceTemplateSearchDirs } from "../../agents/workspace-templ
 import { resolveDefaultAgentWorkspaceDir } from "../../agents/workspace.js";
 import { handleReset } from "../../commands/onboard-helpers.js";
 import { createConfigIO, replaceConfigFile } from "../../config/config.js";
+import { LEGACY_IMPLICIT_AGENT_ID } from "../../routing/session-key.js";
 import { defaultRuntime } from "../../runtime.js";
 import { resolveUserPath, shortenHomePath } from "../../utils.js";
 
@@ -128,6 +129,9 @@ export async function ensureDevGatewayConfig(opts: { reset?: boolean }) {
       },
     },
     afterWrite: { mode: "auto" },
+    // An absent config resolves to the implicit legacy agent before this full
+    // replacement. Declare only that synthetic deletion; authored rosters stay protected.
+    writeOptions: { allowedAgentRosterRemovals: [LEGACY_IMPLICIT_AGENT_ID] },
   });
   await ensureDevWorkspace(workspace);
   defaultRuntime.log(`Dev config ready: ${shortenHomePath(configPath)}`);