feat(canvas): demo Mock #1 — purchase-success modal on URL flag

Funding-demo Mock #1: when the canvas loads with `?purchase_success=1`,
show a centred success modal in the warm-paper theme. Auto-dismisses
after 5s; Close button + Esc + backdrop click also dismiss; URL params
are stripped on first paint so a refresh after dismiss does not
re-trigger.

Mounted in `app/layout.tsx` (not `app/page.tsx`) so the modal persists
across the canvas page-state transitions (loading → hydrated → error)
without unmounting and losing its open-state.

No real billing logic — the marketplace "Purchase" button on the
landing page redirects here with the flag; this modal is the only
thing the user sees of the "transaction".

Local-verified end-to-end via playwright (5/5 tests pass): redirect
URL shape, modal visibility, URL cleanup, close button, refresh-after-
dismiss behaviour, 5s auto-dismiss.

Pairs with the Purchase button added to landingpage Marketplace
section.

canvas/src/app/layout.tsx

@@ -3,6 +3,7 @@ import { cookies, headers } from "next/headers";
 import "./globals.css";
 import { AuthGate } from "@/components/AuthGate";
 import { CookieConsent } from "@/components/CookieConsent";
+import { PurchaseSuccessModal } from "@/components/PurchaseSuccessModal";
 import { ThemeProvider } from "@/lib/theme-provider";
 import {
   THEME_COOKIE,
@@ -86,6 +87,12 @@ export default async function RootLayout({
               vercel preview URL, apex) pass through unchanged. */}
           <AuthGate>{children}</AuthGate>
           <CookieConsent />
+          {/* Demo Mock #1: post-purchase success toast. Mounted at the
+              layout level so it persists across page state transitions
+              (loading → hydrated → error) without being unmounted and
+              losing its open-state. Reads ?purchase_success=1 from the
+              URL on first paint, then strips the param. */}
+          <PurchaseSuccessModal />
         </ThemeProvider>
       </body>
     </html>

canvas/src/components/PurchaseSuccessModal.tsx

@@ -0,0 +1,175 @@
+"use client";
+
+/**
+ * PurchaseSuccessModal — demo-only post-purchase confirmation.
+ *
+ * Mounted on the canvas root (`app/page.tsx`). On first paint it inspects
+ * `?purchase_success=1[&item=<name>]` on the current URL. If present, it
+ * renders a centred modal styled after `ConfirmDialog`, schedules a 5s
+ * auto-dismiss, and rewrites the URL via `history.replaceState` to drop
+ * the params so a refresh after dismiss does NOT re-show the modal.
+ *
+ * Mock for the funding demo — there is no real billing surface behind
+ * this. The marketplace "Purchase" button on the landing page redirects
+ * here with the params; this modal is the only thing the user sees of
+ * the "transaction".
+ *
+ * Styling matches the warm-paper @theme tokens (surface-sunken / line /
+ * ink / good) so it tracks light + dark without per-mode overrides.
+ */
+
+import { useEffect, useRef, useState } from "react";
+import { createPortal } from "react-dom";
+
+const AUTO_DISMISS_MS = 5000;
+
+function readPurchaseParams(): { open: boolean; item: string | null } {
+  if (typeof window === "undefined") return { open: false, item: null };
+  const sp = new URLSearchParams(window.location.search);
+  const flag = sp.get("purchase_success");
+  if (flag !== "1" && flag !== "true") return { open: false, item: null };
+  return { open: true, item: sp.get("item") };
+}
+
+function stripPurchaseParams() {
+  if (typeof window === "undefined") return;
+  const url = new URL(window.location.href);
+  url.searchParams.delete("purchase_success");
+  url.searchParams.delete("item");
+  // replaceState (not pushState) so back-button doesn't return to the
+  // pre-strip URL and re-trigger the modal.
+  window.history.replaceState({}, "", url.toString());
+}
+
+export function PurchaseSuccessModal() {
+  const [open, setOpen] = useState(false);
+  const [item, setItem] = useState<string | null>(null);
+  const [mounted, setMounted] = useState(false);
+  const dialogRef = useRef<HTMLDivElement>(null);
+
+  // Read the URL params once on mount. We don't subscribe to navigation —
+  // this modal is a one-shot for the demo redirect, not a persistent
+  // listener.
+  useEffect(() => {
+    setMounted(true);
+    const { open: shouldOpen, item: itemName } = readPurchaseParams();
+    if (shouldOpen) {
+      setOpen(true);
+      setItem(itemName);
+      // Clean the URL immediately so a refresh after the modal is closed
+      // (or even while it's still open) does NOT re-trigger it.
+      stripPurchaseParams();
+    }
+  }, []);
+
+  // Auto-dismiss timer + Escape handler.
+  useEffect(() => {
+    if (!open) return;
+    const t = window.setTimeout(() => setOpen(false), AUTO_DISMISS_MS);
+    const onKey = (e: KeyboardEvent) => {
+      if (e.key === "Escape") setOpen(false);
+    };
+    window.addEventListener("keydown", onKey);
+    // Focus the close button so keyboard users land on it after redirect.
+    const raf = requestAnimationFrame(() => {
+      dialogRef.current?.querySelector<HTMLButtonElement>("button")?.focus();
+    });
+    return () => {
+      window.clearTimeout(t);
+      window.removeEventListener("keydown", onKey);
+      cancelAnimationFrame(raf);
+    };
+  }, [open]);
+
+  if (!open || !mounted) return null;
+
+  const itemLabel = item ? decodeURIComponent(item) : "Your new agent";
+
+  return createPortal(
+    <div
+      className="fixed inset-0 z-[9999] flex items-center justify-center"
+      data-testid="purchase-success-modal"
+    >
+      {/* Backdrop — click closes, matches ConfirmDialog backdrop. */}
+      <div
+        className="absolute inset-0 bg-black/60 backdrop-blur-sm"
+        onClick={() => setOpen(false)}
+        aria-hidden="true"
+      />
+
+      <div
+        ref={dialogRef}
+        role="dialog"
+        aria-modal="true"
+        aria-labelledby="purchase-success-title"
+        className="relative bg-surface-sunken border border-line rounded-xl shadow-2xl shadow-black/50 max-w-[420px] w-full mx-4 overflow-hidden"
+      >
+        <div className="px-6 pt-6 pb-4">
+          <div className="flex items-start gap-4">
+            {/* Success glyph — uses --color-good so it tracks the theme.
+                Inline SVG over an emoji so it stays readable + on-brand
+                in both light and dark. */}
+            <div
+              className="flex h-10 w-10 flex-shrink-0 items-center justify-center rounded-full"
+              style={{
+                background:
+                  "color-mix(in srgb, var(--color-good) 15%, transparent)",
+                color: "var(--color-good)",
+              }}
+            >
+              <svg
+                width="22"
+                height="22"
+                viewBox="0 0 24 24"
+                fill="none"
+                aria-hidden="true"
+              >
+                <circle
+                  cx="12"
+                  cy="12"
+                  r="10"
+                  stroke="currentColor"
+                  strokeWidth="1.5"
+                />
+                <path
+                  d="M7.5 12.5L10.5 15.5L16.5 9.5"
+                  stroke="currentColor"
+                  strokeWidth="1.8"
+                  strokeLinecap="round"
+                  strokeLinejoin="round"
+                />
+              </svg>
+            </div>
+            <div className="flex-1">
+              <h3
+                id="purchase-success-title"
+                className="text-base font-semibold text-ink"
+              >
+                Purchase successful
+              </h3>
+              <p className="mt-1.5 text-[13px] leading-relaxed text-ink-mid">
+                <span className="font-medium text-ink">{itemLabel}</span> has
+                been added to your workspace. Provisioning starts in the
+                background — you can keep working while it spins up.
+              </p>
+            </div>
+          </div>
+        </div>
+
+        <div className="flex items-center justify-between gap-3 px-6 py-3 border-t border-line bg-surface/50">
+          <span className="font-mono text-[10.5px] uppercase tracking-[0.12em] text-ink-soft">
+            auto-dismiss · {AUTO_DISMISS_MS / 1000}s
+          </span>
+          <button
+            type="button"
+            onClick={() => setOpen(false)}
+            className="px-3.5 py-1.5 text-[13px] rounded-lg bg-accent hover:bg-accent-strong text-white transition-colors focus:outline-none focus-visible:ring-2 focus-visible:ring-offset-2 focus-visible:ring-offset-surface-sunken focus-visible:ring-accent/60"
+          >
+            Close
+          </button>
+        </div>
+      </div>
+    </div>,
+    document.body,
+  );
+}