diff --git a/src/lib/onboard/machine/flow-slices.test.ts b/src/lib/onboard/machine/flow-slices.test.ts
new file mode 100644
index 0000000000..5afd843e4a
--- /dev/null
+++ b/src/lib/onboard/machine/flow-slices.test.ts
@@ -0,0 +1,135 @@
+// SPDX-FileCopyrightText: Copyright (c) 2026 NVIDIA CORPORATION & AFFILIATES. All rights reserved.
+// SPDX-License-Identifier: Apache-2.0
+
+import { describe, expect, it } from "vitest";
+
+import {
+  createSession,
+  filterSafeUpdates,
+  MACHINE_SNAPSHOT_VERSION,
+  normalizeSession,
+  type Session,
+  type SessionUpdates,
+} from "../../state/onboard-session";
+import type { OnboardFlowContext } from "./flow-context";
+import { advanceTo } from "./result";
+import { OnboardRuntime, type OnboardRuntimeDeps } from "./runtime";
+import type { OnboardSequencePhase } from "./sequence-runner";
+import { initialOnboardFlowPhases, runInitialOnboardFlowSequence } from "./flow-slices";
+
+function cloneSession(session: Session): Session {
+  return normalizeSession(JSON.parse(JSON.stringify(session))) ?? session;
+}
+
+function runtime(initialSession: Session = createSession()) {
+  let session = cloneSession(initialSession);
+  const updateSession = (mutator: (value: Session) => Session | void): Session => {
+    session = cloneSession(mutator(cloneSession(session)) ?? session);
+    return cloneSession(session);
+  };
+  const deps: OnboardRuntimeDeps = {
+    loadSession: () => cloneSession(session),
+    createSession,
+    saveSession: (next) => {
+      session = cloneSession(next);
+      return cloneSession(session);
+    },
+    updateSession,
+    markStepStarted: () => cloneSession(session),
+    markStepComplete: (_stepName, updates: SessionUpdates = {}) =>
+      updateSession((current) => Object.assign(current, filterSafeUpdates(updates))),
+    markStepCompleteRecordOnly: (_stepName, updates: SessionUpdates = {}) =>
+      updateSession((current) => Object.assign(current, filterSafeUpdates(updates))),
+    markStepSkipped: () => cloneSession(session),
+    markStepFailed: () => cloneSession(session),
+    markStepFailedRecordOnly: () => cloneSession(session),
+    completeSession: () => cloneSession(session),
+    filterSafeUpdates,
+    emitEvent: () => undefined,
+    now: () => "2026-05-29T00:00:00.000Z",
+  };
+  return new OnboardRuntime(deps);
+}
+
+function context(): OnboardFlowContext {
+  return {
+    resume: false,
+    fresh: false,
+    session: createSession(),
+    agent: null,
+    recordedSandboxName: null,
+    requestedSandboxName: null,
+    sandboxName: null,
+    fromDockerfile: null,
+    model: null,
+    provider: null,
+    endpointUrl: null,
+    credentialEnv: null,
+    hermesAuthMethod: null,
+    hermesToolGateways: [],
+    preferredInferenceApi: null,
+    nimContainer: null,
+    webSearchConfig: null,
+    webSearchSupported: false,
+    selectedMessagingChannels: [],
+    gpu: null,
+    sandboxGpuConfig: null,
+    gpuPassthrough: false,
+  };
+}
+
+function phase(
+  state: OnboardSequencePhase<OnboardFlowContext>["state"],
+  next: ReturnType<typeof advanceTo>["next"],
+): OnboardSequencePhase<OnboardFlowContext> {
+  return { state, run: (ctx) => ({ context: ctx, result: advanceTo(next) }) };
+}
+
+describe("onboard flow slices", () => {
+  it("selects only initial preflight/gateway phases", () => {
+    expect(
+      initialOnboardFlowPhases([
+        phase("preflight", "gateway"),
+        phase("gateway", "provider_selection"),
+        phase("provider_selection", "inference"),
+      ]).map((entry) => entry.state),
+    ).toEqual(["init", "preflight", "gateway"]);
+  });
+
+  it("runs the initial slice from a default session and stops at provider selection", async () => {
+    const result = await runInitialOnboardFlowSequence({
+      context: context(),
+      runtime: runtime(),
+      phases: [
+        phase("preflight", "gateway"),
+        phase("gateway", "provider_selection"),
+        phase("provider_selection", "inference"),
+      ],
+    });
+
+    expect(result.session.machine.state).toBe("provider_selection");
+  });
+
+  it("runs the initial slice from preflight and stops at provider selection", async () => {
+    const result = await runInitialOnboardFlowSequence({
+      context: context(),
+      runtime: runtime(
+        createSession({
+          machine: {
+            version: MACHINE_SNAPSHOT_VERSION,
+            state: "preflight",
+            stateEnteredAt: "2026-05-29T00:00:00.000Z",
+            revision: 0,
+          },
+        }),
+      ),
+      phases: [
+        phase("preflight", "gateway"),
+        phase("gateway", "provider_selection"),
+        phase("provider_selection", "inference"),
+      ],
+    });
+
+    expect(result.session.machine.state).toBe("provider_selection");
+  });
+});
diff --git a/src/lib/onboard/machine/flow-slices.ts b/src/lib/onboard/machine/flow-slices.ts
new file mode 100644
index 0000000000..bf88e7e75b
--- /dev/null
+++ b/src/lib/onboard/machine/flow-slices.ts
@@ -0,0 +1,33 @@
+// SPDX-FileCopyrightText: Copyright (c) 2026 NVIDIA CORPORATION & AFFILIATES. All rights reserved.
+// SPDX-License-Identifier: Apache-2.0
+
+import type { OnboardFlowContext } from "./flow-context";
+import { onboardFlowPhaseResult } from "./flow-context";
+import { advanceTo } from "./result";
+import type { OnboardMachineRunnerRuntime } from "./runner";
+import type { OnboardSequencePhase } from "./sequence-runner";
+import { runOnboardSequenceWithRunner } from "./sequence-runner";
+
+export function initialOnboardFlowPhases<Context extends OnboardFlowContext>(
+  phases: readonly OnboardSequencePhase<Context>[],
+): OnboardSequencePhase<Context>[] {
+  return [
+    {
+      state: "init",
+      run: (context) => onboardFlowPhaseResult(context, advanceTo("preflight")),
+    },
+    ...phases.filter((phase) => phase.state === "preflight" || phase.state === "gateway"),
+  ];
+}
+
+export async function runInitialOnboardFlowSequence<Context extends OnboardFlowContext>(options: {
+  context: Context;
+  runtime: OnboardMachineRunnerRuntime;
+  phases: readonly OnboardSequencePhase<Context>[];
+}) {
+  return runOnboardSequenceWithRunner({
+    ...options,
+    phases: initialOnboardFlowPhases(options.phases),
+    stopStates: ["provider_selection"],
+  });
+}
diff --git a/src/lib/onboard/machine/sequence-runner.ts b/src/lib/onboard/machine/sequence-runner.ts
index 6a9f5e86e4..b2d71a18e6 100644
--- a/src/lib/onboard/machine/sequence-runner.ts
+++ b/src/lib/onboard/machine/sequence-runner.ts
@@ -27,6 +27,7 @@ export interface OnboardSequenceRunnerOptions<Context> {
   phases: readonly OnboardSequencePhase<Context>[];
   maxTransitions?: OnboardMachineRunnerOptions<Context>["maxTransitions"];
   sequenceOwnership?: OnboardMachineRunnerOptions<Context>["sequenceOwnership"];
+  stopStates?: OnboardMachineRunnerOptions<Context>["stopStates"];
 }
 
 export class DuplicateOnboardSequencePhaseError extends Error {
@@ -69,6 +70,7 @@ export async function runOnboardSequenceWithRunner<Context>({
   phases,
   maxTransitions,
   sequenceOwnership,
+  stopStates,
 }: OnboardSequenceRunnerOptions<Context>) {
   let pendingContext = initialContext;
   return runOnboardMachine({
@@ -76,6 +78,7 @@ export async function runOnboardSequenceWithRunner<Context>({
     runtime,
     maxTransitions,
     sequenceOwnership,
+    stopStates,
     handlers: buildOnboardSequenceHandlers(phases, (context) => {
       pendingContext = context;
     }),