diff --git a/apps/fabro-web/app/components/playground/files/render-toml.test.ts b/apps/fabro-web/app/components/playground/files/render-toml.test.ts
index 22b143711..a1599dee2 100644
--- a/apps/fabro-web/app/components/playground/files/render-toml.test.ts
+++ b/apps/fabro-web/app/components/playground/files/render-toml.test.ts
@@ -4,7 +4,10 @@ import { createInitialDraft } from "../state/draft";
 import { renderProjectToml, renderWorkflowToml } from "./render-toml";
 
 describe("renderWorkflowToml", () => {
-  test("points the workflow at workflow.fabro and pins sandbox to local", () => {
+  test("points the workflow at its graph without an unsupported [run.sandbox] section", () => {
+    // The server's RunLayer parses workflow.toml with deny_unknown_fields and
+    // has no `sandbox` field, so a `[run.sandbox]` section makes the manifest
+    // unparseable. Sandbox selection lives in project.toml instead.
     expect(renderWorkflowToml(createInitialDraft())).toBe(
       [
         "_version = 1",
@@ -12,16 +15,13 @@ describe("renderWorkflowToml", () => {
         "[workflow]",
         'graph = "workflow.fabro"',
         "",
-        "[run.sandbox]",
-        'provider = "local"',
-        "",
       ].join("\n"),
     );
   });
 });
 
 describe("renderProjectToml", () => {
-  test("enables draft PRs by default", () => {
+  test("enables draft PRs and pins the default environment to the local sandbox", () => {
     expect(renderProjectToml(createInitialDraft())).toBe(
       [
         "_version = 1",
@@ -30,6 +30,9 @@ describe("renderProjectToml", () => {
         "enabled = true",
         "draft   = true",
         "",
+        "[environments.default]",
+        'provider = "local"',
+        "",
       ].join("\n"),
     );
   });
diff --git a/apps/fabro-web/app/components/playground/files/render-toml.ts b/apps/fabro-web/app/components/playground/files/render-toml.ts
index 7218f82e4..f680d107d 100644
--- a/apps/fabro-web/app/components/playground/files/render-toml.ts
+++ b/apps/fabro-web/app/components/playground/files/render-toml.ts
@@ -12,9 +12,11 @@ import type { WorkflowDraft } from "../state/draft";
 /**
  * The contents of `.fabro/workflows/<name>/workflow.toml`.
  *
- * Points the workflow at its `.fabro` graph and pins the sandbox provider to
- * `local` so the downloaded artifact runs against the user's own machine
- * without any further setup.
+ * Points the workflow at its `.fabro` graph. Sandbox selection deliberately
+ * does NOT live here: the server parses this file into a `RunLayer` with
+ * `deny_unknown_fields` and no `sandbox` field, so a `[run.sandbox]` section
+ * makes the whole run manifest unparseable. The local sandbox is pinned at the
+ * project level instead — see `renderProjectToml`.
  */
 export function renderWorkflowToml(_draft: WorkflowDraft): string {
   return [
@@ -23,17 +25,17 @@ export function renderWorkflowToml(_draft: WorkflowDraft): string {
     "[workflow]",
     'graph = "workflow.fabro"',
     "",
-    "[run.sandbox]",
-    'provider = "local"',
-    "",
   ].join("\n");
 }
 
 /**
  * The contents of `.fabro/project.toml`.
  *
- * Mirrors the defaults shown in the explainer: PRs enabled and draft, so
- * a successful run opens a draft PR the user can review.
+ * Mirrors the defaults shown in the explainer: PRs enabled and draft, so a
+ * successful run opens a draft PR the user can review. Also pins the default
+ * environment to the `local` sandbox so the workflow runs against the user's
+ * own machine without any further setup (the supported home for sandbox
+ * selection, unlike workflow.toml's rejected `[run.sandbox]`).
  */
 export function renderProjectToml(_draft: WorkflowDraft): string {
   return [
@@ -43,5 +45,8 @@ export function renderProjectToml(_draft: WorkflowDraft): string {
     "enabled = true",
     "draft   = true",
     "",
+    "[environments.default]",
+    'provider = "local"',
+    "",
   ].join("\n");
 }
diff --git a/apps/fabro-web/app/components/playground/playground.tsx b/apps/fabro-web/app/components/playground/playground.tsx
index 98a6808c1..ea6733670 100644
--- a/apps/fabro-web/app/components/playground/playground.tsx
+++ b/apps/fabro-web/app/components/playground/playground.tsx
@@ -14,6 +14,7 @@ import DownloadButton from "./ui/download-button";
 import NodeInspector from "./ui/node-inspector";
 import ResetButton from "./ui/reset-button";
 import RunForRealButton, { type RealRunRedirect } from "./ui/run-for-real-button";
+import SaveToRunsButton from "./ui/save-to-runs-button";
 import RunTrace from "./ui/run-trace";
 import SimulationControls from "./ui/simulation-controls";
 import WorkflowHeader from "./ui/workflow-header";
@@ -113,6 +114,7 @@ export default function Playground({
           <div className="ml-auto flex items-center gap-2">
             <ResetButton onReset={handleReset} />
             <DownloadButton draft={draft} />
+            <SaveToRunsButton draft={draft} />
             <RunForRealButton draft={draft} redirect={realRunRedirect} />
             {!isChatOpen && (
               <button
diff --git a/apps/fabro-web/app/components/playground/state/build-manifest.test.ts b/apps/fabro-web/app/components/playground/state/build-manifest.test.ts
index 25410b994..5e7b08a2b 100644
--- a/apps/fabro-web/app/components/playground/state/build-manifest.test.ts
+++ b/apps/fabro-web/app/components/playground/state/build-manifest.test.ts
@@ -35,7 +35,21 @@ describe("buildRunManifest", () => {
     expect(workflow!.source).toContain("digraph");
     expect(workflow!.source).toContain("start ->");
     expect(workflow!.config?.path).toBe("workflow.toml");
-    expect(workflow!.config?.source).toContain("[run.sandbox]");
+    // workflow.toml must stay parseable by the server's RunLayer, which
+    // rejects the unknown `[run.sandbox]` section.
+    expect(workflow!.config?.source).not.toContain("[run.sandbox]");
+    expect(workflow!.config?.source).toContain("[workflow]");
+  });
+
+  test("clamps an over-long goal so the title stays within the server's 100-char limit", () => {
+    const goal = "a".repeat(150);
+    const draft = { ...createInitialDraft(), name: "release_notes", goal };
+    const manifest = buildRunManifest(draft);
+    expect(manifest.title).toBeDefined();
+    // Server caps RunManifest.title at 100 Unicode scalar values; count by
+    // code point (not UTF-16 units) to match its `chars().count()` check.
+    expect(Array.from(manifest.title!).length).toBeLessThanOrEqual(100);
+    expect(manifest.title!.endsWith("…")).toBe(true);
   });
 
   test("named draft → title and identifier use the snake_case name", () => {
diff --git a/apps/fabro-web/app/components/playground/state/build-manifest.ts b/apps/fabro-web/app/components/playground/state/build-manifest.ts
index 6da804913..b3e7c5896 100644
--- a/apps/fabro-web/app/components/playground/state/build-manifest.ts
+++ b/apps/fabro-web/app/components/playground/state/build-manifest.ts
@@ -22,6 +22,26 @@ import {
  */
 const PLAYGROUND_CWD = "/tmp/fabro-playground";
 
+/**
+ * Server-side cap on `RunManifest.title` (`MAX_RUN_TITLE_CHARS`), counted in
+ * Unicode scalar values. Titles longer than this are rejected at run creation,
+ * so we clamp the goal-derived title here to keep "Save to Runs" working for
+ * long goals.
+ */
+const MAX_TITLE_CHARS = 100;
+
+/**
+ * Clamp a candidate title to the server's character limit, counting by code
+ * point (matching Rust's `chars().count()`) rather than UTF-16 units. When it
+ * overflows, keep the first `MAX_TITLE_CHARS - 1` code points and append an
+ * ellipsis so the result is exactly at the limit.
+ */
+function clampTitle(title: string): string {
+  const codePoints = Array.from(title);
+  if (codePoints.length <= MAX_TITLE_CHARS) return title;
+  return `${codePoints.slice(0, MAX_TITLE_CHARS - 1).join("")}…`;
+}
+
 /**
  * Minimal subset of `RunManifest` the playground needs to send. The
  * generated `RunManifest` type from `@qltysh/fabro-api-client` accepts
@@ -65,7 +85,7 @@ export function buildRunManifest(draft: WorkflowDraft): PlaygroundRunManifest {
   return {
     version: 1,
     cwd:     PLAYGROUND_CWD,
-    title:   draft.goal && draft.goal.length > 0 ? draft.goal : `Playground: ${name}`,
+    title:   draft.goal && draft.goal.length > 0 ? clampTitle(draft.goal) : `Playground: ${name}`,
     target:  {
       identifier: name,
       path:       workflowPath,
diff --git a/apps/fabro-web/app/components/playground/ui/save-to-runs-button.test.tsx b/apps/fabro-web/app/components/playground/ui/save-to-runs-button.test.tsx
new file mode 100644
index 000000000..76f65abee
--- /dev/null
+++ b/apps/fabro-web/app/components/playground/ui/save-to-runs-button.test.tsx
@@ -0,0 +1,132 @@
+import { afterEach, describe, expect, test } from "bun:test";
+import TestRenderer, { act } from "react-test-renderer";
+
+import SaveToRunsButton from "./save-to-runs-button";
+import { createInitialDraft, type WorkflowDraft } from "../state/draft";
+
+function withPlan(): WorkflowDraft {
+  return {
+    name:  "release_notes",
+    goal:  "Generate release notes.",
+    nodes: [
+      { id: "start", label: "Start", shape: "mdiamond" },
+      { id: "exit", label: "Exit", shape: "msquare" },
+      { id: "plan", label: "Plan", shape: "box", prompt: "Plan it." },
+    ],
+    edges: [
+      { from: "start", to: "plan" },
+      { from: "plan", to: "exit" },
+    ],
+  };
+}
+
+function render(node: React.ReactNode): TestRenderer.ReactTestRenderer {
+  let tree: TestRenderer.ReactTestRenderer | undefined;
+  act(() => {
+    tree = TestRenderer.create(node as TestRenderer.ReactTestRendererJSON);
+  });
+  return tree!;
+}
+
+type CapturedRequest = { url: string; method?: string; body: unknown };
+
+function stubFetch(
+  responder: (req: CapturedRequest) => {
+    ok: boolean;
+    status: number;
+    statusText?: string;
+    body?: unknown;
+  },
+): { requests: CapturedRequest[] } {
+  const requests: CapturedRequest[] = [];
+  globalThis.fetch = (async (url: string, init?: RequestInit) => {
+    const req: CapturedRequest = {
+      url:    String(url),
+      method: init?.method,
+      body:   init?.body ? JSON.parse(String(init.body)) : undefined,
+    };
+    requests.push(req);
+    const res = responder(req);
+    const payload = res.body ?? null;
+    return {
+      ok:         res.ok,
+      status:     res.status,
+      statusText: res.statusText ?? "",
+      json:       async () => payload,
+      clone:      () => ({ json: async () => payload }),
+    } as unknown as Response;
+  }) as typeof fetch;
+  return { requests };
+}
+
+const originalFetch = globalThis.fetch;
+
+function findButton(tree: TestRenderer.ReactTestRenderer) {
+  return tree.root.findByProps({ "aria-label": "Save to Runs" });
+}
+
+async function clickAndSettle(
+  el: TestRenderer.ReactTestInstance,
+): Promise<void> {
+  await act(async () => {
+    el.props.onClick();
+    await Promise.resolve();
+    await Promise.resolve();
+    await Promise.resolve();
+  });
+}
+
+describe("SaveToRunsButton", () => {
+  afterEach(() => {
+    globalThis.fetch = originalFetch;
+  });
+
+  test("POSTs the manifest to /api/v1/runs and links to the new run without starting it", async () => {
+    const stub = stubFetch(() => ({
+      ok:     true,
+      status: 201,
+      body:   { id: "run-9" },
+    }));
+
+    const tree = render(<SaveToRunsButton draft={withPlan()} />);
+    await clickAndSettle(findButton(tree));
+
+    // Exactly one request: create. No /start call (create-only).
+    expect(stub.requests).toHaveLength(1);
+    expect(stub.requests[0]!.url).toBe("/api/v1/runs");
+    expect(stub.requests[0]!.method?.toUpperCase()).toBe("POST");
+    expect(stub.requests.some((r) => r.url.includes("/start"))).toBe(false);
+
+    const manifest = stub.requests[0]!.body as {
+      version: number;
+      target: { identifier: string };
+    };
+    expect(manifest.version).toBe(1);
+    expect(manifest.target.identifier).toBe("release_notes");
+
+    // Success surfaces a link into the runs list for the created run.
+    expect(tree.root.findByProps({ href: "/runs/run-9" })).toBeDefined();
+  });
+
+  test("is disabled in the welcome state", () => {
+    const tree = render(<SaveToRunsButton draft={createInitialDraft()} />);
+    expect(findButton(tree).props.disabled).toBe(true);
+  });
+
+  test("surfaces the server error detail and creates no run link on failure", async () => {
+    const stub = stubFetch(() => ({
+      ok:         false,
+      status:     400,
+      statusText: "Bad Request",
+      body:       { errors: [{ status: "400", title: "Bad Request", detail: "Validation failed" }] },
+    }));
+
+    const tree = render(<SaveToRunsButton draft={withPlan()} />);
+    await clickAndSettle(findButton(tree));
+
+    expect(stub.requests).toHaveLength(1);
+    const alert = tree.root.findByProps({ role: "alert" });
+    expect(alert.props.title).toContain("Validation failed");
+    expect(tree.root.findAllByProps({ href: "/runs/run-9" })).toHaveLength(0);
+  });
+});
diff --git a/apps/fabro-web/app/components/playground/ui/save-to-runs-button.tsx b/apps/fabro-web/app/components/playground/ui/save-to-runs-button.tsx
new file mode 100644
index 000000000..d4308935a
--- /dev/null
+++ b/apps/fabro-web/app/components/playground/ui/save-to-runs-button.tsx
@@ -0,0 +1,112 @@
+import { useState } from "react";
+import {
+  ArchiveBoxArrowDownIcon,
+  CheckCircleIcon,
+  ExclamationTriangleIcon,
+} from "@heroicons/react/24/outline";
+
+import { buildRunManifest } from "../state/build-manifest";
+import type { WorkflowDraft } from "../state/draft";
+import { isWelcomeState } from "../state/draft";
+
+type SaveState =
+  | { kind: "idle" }
+  | { kind: "saving" }
+  | { kind: "saved"; runId: string }
+  | { kind: "error"; message: string };
+
+const BUTTON_CLASS =
+  "inline-flex items-center gap-1.5 rounded-md bg-sky-500/10 px-3 py-1.5 text-sm font-medium text-sky-200 ring-1 ring-sky-500/30 transition-colors hover:bg-sky-500/20 hover:text-sky-100 focus-visible:outline-2 focus-visible:outline-offset-2 focus-visible:outline-sky-500 disabled:cursor-not-allowed disabled:opacity-40 disabled:hover:bg-sky-500/10 disabled:hover:text-sky-200";
+
+/**
+ * "Save to Runs" toolbar button.
+ *
+ * Submits the finalized playground pipeline to `POST /api/v1/runs`, which
+ * creates the run in the `submitted` state and lands it in the runs list —
+ * without starting execution (that stays a deliberate, separate action from
+ * the run page). On success the button morphs into a link into the runs list;
+ * on failure it surfaces the server's error detail inline.
+ *
+ * Disabled in the welcome state — saving an empty `start → exit` skeleton is
+ * pointless.
+ */
+export default function SaveToRunsButton({ draft }: { draft: WorkflowDraft }) {
+  const [state, setState] = useState<SaveState>({ kind: "idle" });
+
+  const isWelcome = isWelcomeState(draft);
+  const disabled = isWelcome || state.kind === "saving";
+
+  const save = async () => {
+    setState({ kind: "saving" });
+    try {
+      const manifest = buildRunManifest(draft);
+      const response = await fetch("/api/v1/runs", {
+        method:      "POST",
+        credentials: "same-origin",
+        headers:     { "Content-Type": "application/json" },
+        body:        JSON.stringify(manifest),
+      });
+      if (!response.ok) {
+        const detail = await readErrorDetail(response);
+        throw new Error(detail ?? `${response.status} ${response.statusText}`);
+      }
+      const body = (await response.json()) as { id?: string };
+      if (!body.id) {
+        throw new Error("Server did not return a run id.");
+      }
+      setState({ kind: "saved", runId: body.id });
+    } catch (e) {
+      setState({ kind: "error", message: e instanceof Error ? e.message : String(e) });
+    }
+  };
+
+  if (state.kind === "saved") {
+    return (
+      <a
+        href={`/runs/${state.runId}`}
+        className="inline-flex items-center gap-1.5 rounded-md bg-emerald-500/10 px-3 py-1.5 text-sm font-medium text-emerald-200 ring-1 ring-emerald-500/30 transition-colors hover:bg-emerald-500/20 hover:text-emerald-100 focus-visible:outline-2 focus-visible:outline-offset-2 focus-visible:outline-emerald-500"
+      >
+        <CheckCircleIcon className="size-4" />
+        Saved — view in Runs
+      </a>
+    );
+  }
+
+  return (
+    <div className="flex items-center gap-2">
+      {state.kind === "error" && (
+        <span
+          role="alert"
+          className="inline-flex max-w-56 items-center gap-1 truncate text-xs text-rose-200"
+          title={state.message}
+        >
+          <ExclamationTriangleIcon className="size-3.5 shrink-0" aria-hidden="true" />
+          {state.message}
+        </span>
+      )}
+      <button
+        type="button"
+        aria-label="Save to Runs"
+        disabled={disabled}
+        title={isWelcome ? "Add at least one node first" : undefined}
+        onClick={save}
+        className={BUTTON_CLASS}
+      >
+        <ArchiveBoxArrowDownIcon className="size-4" />
+        {state.kind === "saving" ? "Saving…" : "Save to Runs"}
+      </button>
+    </div>
+  );
+}
+
+async function readErrorDetail(response: Response): Promise<string | null> {
+  try {
+    const body = (await response.clone().json()) as {
+      errors?: { detail?: string; title?: string }[];
+    };
+    const first = body.errors?.[0];
+    return first?.detail ?? first?.title ?? null;
+  } catch {
+    return null;
+  }
+}