diff --git a/.gitignore b/.gitignore
index 69bf1e7..1224283 100644
--- a/.gitignore
+++ b/.gitignore
@@ -17,3 +17,4 @@ artifacts/
 uploads/
 *.zip
 .vite/
+data/credited-donation-sigs/
diff --git a/README.md b/README.md
index a7e6ee5..9338964 100644
--- a/README.md
+++ b/README.md
@@ -35,6 +35,11 @@ SITE_URL=https://shipx402.com
 
 Optional RPC for donation verification (see `src/lib` donate / solana config).
 
+Durable donation receipt replay (required in production): set
+`KV_REST_API_URL` + `KV_REST_API_TOKEN` (Vercel KV / Upstash). Local/dev
+falls back to `data/credited-donation-sigs/` (gitignored). Receipts fail
+closed if the store cannot claim a signature.
+
 ## Deploy notes
 
 - Stack: TanStack Start + Vite + Nitro (Vercel preset on build)
diff --git a/package-lock.json b/package-lock.json
index 8545664..c5d9914 100644
--- a/package-lock.json
+++ b/package-lock.json
@@ -76,6 +76,7 @@
         "nitro": "3.0.260603-beta",
         "playwright": "^1.52.0",
         "prettier": "^3.4.0",
+        "tsx": "^4.23.13",
         "typescript": "^5.7.0",
         "typescript-eslint": "^8.56.1",
         "vite": "^8.1.0"
@@ -402,6 +403,448 @@
         "tslib": "^2.4.0"
       }
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+      "license": "MIT",
+      "optional": true,
+      "os": [
+        "win32"
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+    "node_modules/@esbuild/win32-x64": {
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     "node_modules/@eslint-community/eslint-utils": {
       "version": "4.10.1",
       "resolved": "https://registry.npmjs.org/@eslint-community/eslint-utils/-/eslint-utils-4.10.1.tgz",
@@ -4898,6 +5341,48 @@
         "es6-promise": "^4.0.3"
       }
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+      "devOptional": true,
+      "hasInstallScript": true,
+      "license": "MIT",
+      "bin": {
+        "esbuild": "bin/esbuild"
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+        "@esbuild/android-arm": "0.28.2",
+        "@esbuild/android-arm64": "0.28.2",
+        "@esbuild/android-x64": "0.28.2",
+        "@esbuild/darwin-arm64": "0.28.2",
+        "@esbuild/darwin-x64": "0.28.2",
+        "@esbuild/freebsd-arm64": "0.28.2",
+        "@esbuild/freebsd-x64": "0.28.2",
+        "@esbuild/linux-arm": "0.28.2",
+        "@esbuild/linux-arm64": "0.28.2",
+        "@esbuild/linux-ia32": "0.28.2",
+        "@esbuild/linux-loong64": "0.28.2",
+        "@esbuild/linux-mips64el": "0.28.2",
+        "@esbuild/linux-ppc64": "0.28.2",
+        "@esbuild/linux-riscv64": "0.28.2",
+        "@esbuild/linux-s390x": "0.28.2",
+        "@esbuild/linux-x64": "0.28.2",
+        "@esbuild/netbsd-arm64": "0.28.2",
+        "@esbuild/netbsd-x64": "0.28.2",
+        "@esbuild/openbsd-arm64": "0.28.2",
+        "@esbuild/openbsd-x64": "0.28.2",
+        "@esbuild/openharmony-arm64": "0.28.2",
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+        "@esbuild/win32-arm64": "0.28.2",
+        "@esbuild/win32-ia32": "0.28.2",
+        "@esbuild/win32-x64": "0.28.2"
+      }
+    },
     "node_modules/escalade": {
       "version": "3.2.0",
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@@ -7358,6 +7843,40 @@
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       "license": "0BSD"
     },
+    "node_modules/tsx": {
+      "version": "4.23.13",
+      "resolved": "https://registry.npmjs.org/tsx/-/tsx-4.23.13.tgz",
+      "integrity": "sha512-BL5MGkRln6aDYhb0xbQlEAGw743BaZYWdbWtdJOBriYJboKgUUYCadFp2/FpBBZquBC/ezNBn7wMMPx7FDZUDw==",
+      "devOptional": true,
+      "license": "MIT",
+      "dependencies": {
+        "esbuild": "~0.28.0"
+      },
+      "bin": {
+        "tsx": "dist/cli.mjs"
+      },
+      "engines": {
+        "node": ">=18.0.0"
+      },
+      "optionalDependencies": {
+        "fsevents": "~2.3.3"
+      }
+    },
+    "node_modules/tsx/node_modules/fsevents": {
+      "version": "2.3.3",
+      "resolved": "https://registry.npmjs.org/fsevents/-/fsevents-2.3.3.tgz",
+      "integrity": "sha512-5xoDfX+fL7faATnagmWPpbFtwh/R77WmMMqqHGS65C3vvB0YHrgF+B1YmZ3441tMj5n63k0212XNoJwzlhffQw==",
+      "dev": true,
+      "hasInstallScript": true,
+      "license": "MIT",
+      "optional": true,
+      "os": [
+        "darwin"
+      ],
+      "engines": {
+        "node": "^8.16.0 || ^10.6.0 || >=11.0.0"
+      }
+    },
     "node_modules/tw-animate-css": {
       "version": "1.4.0",
       "resolved": "https://registry.npmjs.org/tw-animate-css/-/tw-animate-css-1.4.0.tgz",
diff --git a/package.json b/package.json
index 909e678..2060767 100644
--- a/package.json
+++ b/package.json
@@ -13,7 +13,8 @@
     "preview": "vite preview --host 0.0.0.0 --port 8080",
     "typecheck": "tsc --noEmit",
     "lint": "eslint .",
-    "format": "prettier --write ."
+    "format": "prettier --write .",
+    "test:p0": "tsx --test src/lib/p0-selftest.test.ts"
   },
   "dependencies": {
     "@hookform/resolvers": "^5.0.0",
@@ -86,6 +87,7 @@
     "nitro": "3.0.260603-beta",
     "playwright": "^1.52.0",
     "prettier": "^3.4.0",
+    "tsx": "^4.23.13",
     "typescript": "^5.7.0",
     "typescript-eslint": "^8.56.1",
     "vite": "^8.1.0"
diff --git a/src/components/create-wallet.tsx b/src/components/create-wallet.tsx
index ef83343..fd2c6b3 100644
--- a/src/components/create-wallet.tsx
+++ b/src/components/create-wallet.tsx
@@ -67,7 +67,7 @@ export function CreateWallet() {
   );
 
   const secretConfirmed =
-    !!secretKey && confirmTail.trim().toLowerCase() === secretTail.toLowerCase();
+    !!secretKey && confirmTail.trim() === secretTail;
 
   const canLeaveSecretStep =
     secretConfirmed && ackWrite && ackShare && ackDevice && !!publicKey && !!secretKey;
@@ -517,6 +517,9 @@ export function CreateWallet() {
                 spellCheck={false}
                 maxLength={6}
               />
+              <p className="mt-1 text-xs text-subtle">
+                Base58 is case-sensitive — match the last 6 characters exactly.
+              </p>
               {confirmTail.length > 0 && (
                 <p
                   className={cn(
diff --git a/src/components/donate-panel.tsx b/src/components/donate-panel.tsx
index 81fc482..9cc7fd2 100644
--- a/src/components/donate-panel.tsx
+++ b/src/components/donate-panel.tsx
@@ -14,10 +14,7 @@ import { Badge } from "@/components/ui/badge";
 import { Button } from "@/components/ui/button";
 import { Card, CardDescription, CardHeader, CardTitle } from "@/components/ui/card";
 import { Input, Label } from "@/components/ui/input";
-import {
-  encodeSolanaPayUrl,
-  type PaymentToken,
-} from "@/lib/solana-pay";
+import { encodeSolanaPayUrl } from "@/lib/solana-pay";
 import {
   DONATION_ADDRESS,
   DONATION_DEFAULT_SOL,
@@ -32,13 +29,12 @@ import { copyText, cn } from "@/lib/utils";
 
 /**
  * Donations for humans (exact wallet QR + Solana Pay link) and agents (x402).
- * The displayed QR is the owner's exact export for DONATION_ADDRESS — not regenerated.
+ * Verify is native SOL only (`onchain-sol`) — USDC is not offered as a receipt path.
  */
 export function DonatePanel() {
   const configured = isDonationAddressConfigured();
 
   const [amount, setAmount] = useState<string>(String(DONATION_DEFAULT_SOL));
-  const [token, setToken] = useState<PaymentToken>("SOL");
   const [checking402, setChecking402] = useState(false);
   const [preview402, setPreview402] = useState<string | null>(null);
   const [receiptSig, setReceiptSig] = useState("");
@@ -52,15 +48,19 @@ export function DonatePanel() {
   const payUrl = useMemo(() => {
     if (!configured) return null;
     const amt = Number(amount);
-    return encodeSolanaPayUrl({
-      recipient: DONATION_ADDRESS,
-      amount: Number.isFinite(amt) && amt > 0 ? amt : undefined,
-      token,
-      label: "Ship x402 donation",
-      message: "Thanks for keeping the tutorial free!",
-      network: "mainnet-beta",
-    });
-  }, [configured, amount, token]);
+    try {
+      return encodeSolanaPayUrl({
+        recipient: DONATION_ADDRESS,
+        amount: Number.isFinite(amt) && amt > 0 ? amt : undefined,
+        token: "SOL",
+        label: "Ship x402 donation",
+        message: "Thanks for keeping the tutorial free!",
+        network: "mainnet-beta",
+      });
+    } catch {
+      return null;
+    }
+  }, [configured, amount]);
 
   const endpointUrl = DONATION_RESOURCE_PATH;
   const endpointUrlAbsolute =
@@ -164,8 +164,8 @@ curl -s https://shipx402.com${DONATION_RESOURCE_PATH} -H "X-PAYMENT: <base64 pro
   }
 
   return (
-    <div className="grid gap-6 lg:grid-cols-2">
-      <Card>
+    <div className="grid min-w-0 grid-cols-1 gap-6 xl:grid-cols-2">
+      <Card className="min-w-0">
         <CardHeader>
           <CardTitle className="flex items-center gap-2">
             <Heart className="size-5 text-primary" />
@@ -176,66 +176,51 @@ curl -s https://shipx402.com${DONATION_RESOURCE_PATH} -H "X-PAYMENT: <base64 pro
             0.25 gets a special thank-you on the receipt — still optional either way.
           </CardDescription>
         </CardHeader>
-        <div className="space-y-4 p-6 pt-0">
+        <div className="min-w-0 space-y-4 p-6 pt-0">
           <div className="flex justify-center">
             <DonationQr size={256} />
           </div>
 
-          <div className="grid gap-3 sm:grid-cols-2">
-            <div>
-              <Label>Amount (SOL)</Label>
-              <Input
-                type="number"
-                min={0}
-                step="0.001"
-                value={amount}
-                onChange={(e) => setAmount(e.target.value)}
-              />
-            </div>
-            <div>
-              <Label>Token</Label>
-              <div className="flex h-11 overflow-hidden rounded-[var(--radius-md)] border border-border">
-                {(["SOL", "USDC"] as const).map((t) => (
-                  <button
-                    key={t}
-                    type="button"
-                    className={cn(
-                      "flex-1 text-sm font-medium transition-colors",
-                      token === t
-                        ? "bg-surface-2 text-fg"
-                        : "bg-bg text-muted hover:text-fg",
-                    )}
-                    onClick={() => setToken(t)}
-                  >
-                    {t}
-                  </button>
-                ))}
-              </div>
-            </div>
+          <div className="min-w-0">
+            <Label>Amount (SOL)</Label>
+            <Input
+              type="number"
+              min={0}
+              step="0.001"
+              value={amount}
+              onChange={(e) => setAmount(e.target.value)}
+              className="min-w-0 w-full"
+            />
+            <p className="mt-1.5 text-xs text-subtle">
+              Receipts verify native SOL only (SystemProgram transfer). USDC is not
+              receipt-eligible.
+            </p>
           </div>
 
-          <div className="grid gap-2 sm:grid-cols-2">
+          <div className="grid grid-cols-1 gap-3">
             {DONATION_TIERS.map((tier) => (
               <button
                 key={tier.sol}
                 type="button"
                 onClick={() => setAmount(String(tier.sol))}
                 className={cn(
-                  "rounded-[var(--radius-md)] border px-3 py-2.5 text-left transition-colors",
+                  "min-w-0 rounded-[var(--radius-md)] border p-4 text-left transition-colors",
                   amount === String(tier.sol)
                     ? "border-primary/40 bg-primary/15"
                     : "border-border bg-surface hover:border-border-strong",
                 )}
               >
-                <div className="flex items-center justify-between gap-2">
-                  <span className="text-sm font-semibold text-fg">{tier.label}</span>
-                  <span className="font-mono text-xs text-primary">
-                    {tier.sol} {token}
+                <div className="flex min-w-0 flex-wrap items-baseline justify-between gap-x-3 gap-y-1">
+                  <span className="min-w-0 break-words text-sm font-semibold text-fg">
+                    {tier.label}
+                  </span>
+                  <span className="shrink-0 font-mono text-xs text-primary">
+                    {tier.sol} SOL
                   </span>
                 </div>
-                <p className="mt-0.5 text-xs text-muted">{tier.blurb}</p>
+                <p className="mt-1 text-xs leading-relaxed text-muted">{tier.blurb}</p>
                 {tier.recommended ? (
-                  <span className="mt-1 inline-block text-[10px] font-semibold uppercase tracking-wide text-primary">
+                  <span className="mt-2 inline-block text-[10px] font-semibold uppercase tracking-wide text-primary">
                     Suggested default
                   </span>
                 ) : null}
@@ -245,18 +230,20 @@ curl -s https://shipx402.com${DONATION_RESOURCE_PATH} -H "X-PAYMENT: <base64 pro
               type="button"
               onClick={() => setAmount("0.5")}
               className={cn(
-                "rounded-[var(--radius-md)] border px-3 py-2.5 text-left transition-colors",
+                "min-w-0 rounded-[var(--radius-md)] border p-4 text-left transition-colors",
                 isGenerousDonation(Number(amount))
                   ? "border-ember/50 bg-ember/15"
                   : "border-border bg-surface hover:border-border-strong",
               )}
               title="Anything above 0.25 SOL gets a special thank-you on the receipt"
             >
-              <div className="flex items-center justify-between gap-2">
-                <span className="text-sm font-semibold text-fg">0.26+ {token}</span>
-                <span className="font-mono text-xs text-ember">generous</span>
+              <div className="flex min-w-0 flex-wrap items-baseline justify-between gap-x-3 gap-y-1">
+                <span className="min-w-0 break-words text-sm font-semibold text-fg">
+                  0.26+ SOL
+                </span>
+                <span className="shrink-0 font-mono text-xs text-ember">generous</span>
               </div>
-              <p className="mt-0.5 text-xs text-muted">
+              <p className="mt-1 text-xs leading-relaxed text-muted">
                 Huge thank-you on the receipt. Edit the amount to any value you like.
               </p>
             </button>
@@ -287,9 +274,9 @@ curl -s https://shipx402.com${DONATION_RESOURCE_PATH} -H "X-PAYMENT: <base64 pro
             payTo). The optional link only pre-fills an amount in compatible wallets.
           </p>
 
-          <div className="rounded-[var(--radius-lg)] border border-primary/25 bg-primary/5 p-4">
+          <div className="min-w-0 rounded-[var(--radius-lg)] border border-border bg-surface p-4">
             <div className="mb-2 flex items-center gap-2 text-base font-semibold text-fg">
-              <Receipt className="size-4 text-primary" />
+              <Receipt className="size-4 text-muted" />
               Get your receipt
             </div>
             <p className="mb-3 text-sm text-muted">
@@ -298,14 +285,17 @@ curl -s https://shipx402.com${DONATION_RESOURCE_PATH} -H "X-PAYMENT: <base64 pro
             </p>
             <Label>Transaction signature</Label>
             <Input
-              className="font-mono text-xs"
-              placeholder="Paste base58 signature from Phantom / Explorer"
+              className="min-w-0 w-full font-mono text-xs"
+              placeholder="Paste base58 tx signature"
               value={receiptSig}
               onChange={(e) => setReceiptSig(e.target.value)}
               autoCapitalize="off"
               autoCorrect="off"
               spellCheck={false}
             />
+            <p className="mt-1.5 text-xs text-subtle">
+              Copy the signature from Phantom (transaction details) or Solana Explorer.
+            </p>
             <Button
               className="mt-3 w-full"
               disabled={receiptBusy || !receiptSig.trim()}
@@ -319,7 +309,7 @@ curl -s https://shipx402.com${DONATION_RESOURCE_PATH} -H "X-PAYMENT: <base64 pro
               Verify & show receipt
             </Button>
             {receiptResult && (
-              <div className="mt-3 space-y-2">
+              <div className="mt-3 min-w-0 space-y-2">
                 {receiptResult.ok &&
                   typeof receiptResult.body === "object" &&
                   receiptResult.body !== null &&
@@ -334,7 +324,7 @@ curl -s https://shipx402.com${DONATION_RESOURCE_PATH} -H "X-PAYMENT: <base64 pro
                   )}
                 <pre
                   className={cn(
-                    "max-h-48 overflow-auto rounded-[var(--radius-md)] border p-3 font-mono text-[11px] leading-relaxed",
+                    "max-h-48 max-w-full min-w-0 overflow-x-auto whitespace-pre rounded-[var(--radius-md)] border p-3 font-mono text-xs leading-relaxed",
                     receiptResult.ok
                       ? "border-success/30 bg-success-bg text-success"
                       : "border-border bg-bg text-muted",
@@ -349,7 +339,7 @@ curl -s https://shipx402.com${DONATION_RESOURCE_PATH} -H "X-PAYMENT: <base64 pro
         </div>
       </Card>
 
-      <Card>
+      <Card className="min-w-0">
         <CardHeader>
           <CardTitle className="flex items-center gap-2">
             <Bot className="size-5 text-primary" />
@@ -360,18 +350,19 @@ curl -s https://shipx402.com${DONATION_RESOURCE_PATH} -H "X-PAYMENT: <base64 pro
             Tips are optional — suggested 0.01 / 0.05 / 0.25 SOL.
           </CardDescription>
         </CardHeader>
-        <div className="space-y-4 p-6 pt-0">
-          <div className="rounded-[var(--radius-md)] border border-border bg-bg p-3">
+        <div className="min-w-0 space-y-4 p-6 pt-0">
+          <div className="min-w-0 rounded-[var(--radius-md)] border border-border bg-bg p-3">
             <div className="mb-1 text-xs font-medium uppercase tracking-wide text-subtle">
               Endpoint
             </div>
-            <div className="flex items-center gap-2">
-              <code className="flex-1 break-all font-mono text-xs text-fg">
+            <div className="flex min-w-0 items-center gap-2">
+              <code className="min-w-0 flex-1 break-all font-mono text-xs text-fg">
                 {endpointUrl}
               </code>
               <Button
                 size="sm"
                 variant="secondary"
+                className="shrink-0"
                 onClick={async () => {
                   await copyText(endpointUrlAbsolute);
                   toast.success("Endpoint copied");
@@ -382,11 +373,15 @@ curl -s https://shipx402.com${DONATION_RESOURCE_PATH} -H "X-PAYMENT: <base64 pro
             </div>
           </div>
 
-          <div className="rounded-[var(--radius-md)] border border-border bg-bg p-3">
+          <div className="min-w-0 rounded-[var(--radius-md)] border border-border bg-bg p-3">
             <div className="mb-1 text-xs font-medium uppercase tracking-wide text-subtle">
               payTo (mainnet)
             </div>
-            <Input readOnly value={DONATION_ADDRESS} className="font-mono text-xs" />
+            <Input
+              readOnly
+              value={DONATION_ADDRESS}
+              className="min-w-0 w-full font-mono text-xs"
+            />
           </div>
 
           <Button
@@ -404,12 +399,12 @@ curl -s https://shipx402.com${DONATION_RESOURCE_PATH} -H "X-PAYMENT: <base64 pro
           </Button>
 
           {preview402 && (
-            <pre className="max-h-56 overflow-auto rounded-[var(--radius-md)] border border-border bg-bg p-3 font-mono text-[11px] text-muted">
+            <pre className="max-h-56 max-w-full min-w-0 overflow-x-auto whitespace-pre rounded-[var(--radius-md)] border border-border bg-bg p-3 font-mono text-xs text-muted">
               {preview402}
             </pre>
           )}
 
-          <pre className="overflow-auto rounded-[var(--radius-md)] border border-border bg-bg p-3 font-mono text-[11px] text-muted">
+          <pre className="max-w-full min-w-0 overflow-x-auto whitespace-pre rounded-[var(--radius-md)] border border-border bg-bg p-3 font-mono text-xs text-muted">
             {curlExample}
           </pre>
 
diff --git a/src/components/donation-qr.tsx b/src/components/donation-qr.tsx
index b64696f..4b99215 100644
--- a/src/components/donation-qr.tsx
+++ b/src/components/donation-qr.tsx
@@ -1,7 +1,6 @@
 import { useEffect, useState } from "react";
 import QRCode from "qrcode";
-import { PublicKey } from "@solana/web3.js";
-import { DONATION_ADDRESS } from "@/lib/donate";
+import { DONATION_ADDRESS, assertDonationAddressValid } from "@/lib/donate";
 import { cn } from "@/lib/utils";
 
 /**
@@ -13,16 +12,6 @@ export function donationPayUri(address = DONATION_ADDRESS) {
   return `solana:${address.trim()}`;
 }
 
-export function assertDonationAddressValid(address = DONATION_ADDRESS): boolean {
-  try {
-    // Throws if not a valid on-curve Solana public key encoding
-    const pk = new PublicKey(address);
-    return pk.toBase58() === address;
-  } catch {
-    return false;
-  }
-}
-
 export function DonationQr({
   className,
   size = 256,
diff --git a/src/components/site-chrome.tsx b/src/components/site-chrome.tsx
index bfea1cb..8df33ff 100644
--- a/src/components/site-chrome.tsx
+++ b/src/components/site-chrome.tsx
@@ -82,7 +82,7 @@ export function SiteChrome({
 
       <main
         id="main-content"
-        className="mx-auto max-w-6xl px-4 py-10 sm:px-6 sm:py-14"
+        className="mx-auto w-full min-w-0 max-w-6xl px-4 py-10 sm:px-6 sm:py-14"
         tabIndex={-1}
       >
         {children}
diff --git a/src/components/ui/input.tsx b/src/components/ui/input.tsx
index 45dc0c8..44f6554 100644
--- a/src/components/ui/input.tsx
+++ b/src/components/ui/input.tsx
@@ -9,7 +9,7 @@ export const Input = React.forwardRef<
     <input
       type={type}
       className={cn(
-        "flex h-11 w-full rounded-[var(--radius-md)] border border-border bg-bg px-3 py-2 text-sm text-fg placeholder:text-subtle focus-visible:outline-none focus-visible:ring-2 focus-visible:ring-primary disabled:cursor-not-allowed disabled:opacity-50",
+        "flex h-11 w-full min-w-0 rounded-[var(--radius-md)] border border-border bg-bg px-3 py-2 text-sm text-fg placeholder:text-subtle focus-visible:outline-none focus-visible:ring-2 focus-visible:ring-primary disabled:cursor-not-allowed disabled:opacity-50",
         className,
       )}
       ref={ref}
diff --git a/src/components/x402-lab.tsx b/src/components/x402-lab.tsx
index 46c0d3a..08debbb 100644
--- a/src/components/x402-lab.tsx
+++ b/src/components/x402-lab.tsx
@@ -139,6 +139,7 @@ export function X402Lab({
         resource: X402_RESOURCE_PATH,
         amount,
         network: accept.network,
+        payTo: accept.payTo,
       });
       setProof(signed);
       const paymentHeader = encodeXPaymentHeader(signed);
diff --git a/src/lib/credited-sig-store.ts b/src/lib/credited-sig-store.ts
new file mode 100644
index 0000000..5ff6ba6
--- /dev/null
+++ b/src/lib/credited-sig-store.ts
@@ -0,0 +1,120 @@
+/**
+ * Durable single-use store for mainnet donation transaction signatures.
+ *
+ * Process-local Maps are not enough: Vercel isolates would re-credit the same
+ * sig. Claim is atomic (Redis SET NX, or O_EXCL file create).
+ *
+ * Backends:
+ *   1. Vercel KV / Upstash Redis REST when KV_REST_API_URL (or
+ *      UPSTASH_REDIS_REST_URL) + matching token are set.
+ *   2. Filesystem directory (CREDITED_SIG_PATH or ./data/credited-donation-sigs).
+ *
+ * If no durable backend can complete the claim, we fail closed — no receipt.
+ */
+
+import { mkdirSync, writeFileSync } from "node:fs";
+import { join } from "node:path";
+
+const KEY_PREFIX = "shipx402:donate:sig:";
+/** Keep longer than DONATION_MAX_AGE_SECONDS so TTL cannot outrun the age check. */
+const DEFAULT_TTL_SECONDS = 6 * 60 * 60;
+
+export type ClaimResult = "ok" | "duplicate";
+
+function kvConfig(): { url: string; token: string } | null {
+  const url = (
+    process.env.KV_REST_API_URL ||
+    process.env.UPSTASH_REDIS_REST_URL ||
+    ""
+  ).trim();
+  const token = (
+    process.env.KV_REST_API_TOKEN ||
+    process.env.UPSTASH_REDIS_REST_TOKEN ||
+    ""
+  ).trim();
+  if (url && token) return { url, token };
+  return null;
+}
+
+function fileDir(): string {
+  const fromEnv = process.env.CREDITED_SIG_PATH?.trim();
+  if (fromEnv) return fromEnv;
+  return join(process.cwd(), "data", "credited-donation-sigs");
+}
+
+function safeSigFileName(signature: string): string {
+  // Solana tx signatures are base58; reject path separators.
+  if (!/^[1-9A-HJ-NP-Za-km-z]+$/.test(signature) || signature.length > 128) {
+    throw new Error("Signature is not a safe replay-store key");
+  }
+  return `${signature}.claimed`;
+}
+
+async function claimRedis(
+  signature: string,
+  ttlSeconds: number,
+): Promise<ClaimResult> {
+  const cfg = kvConfig();
+  if (!cfg) throw new Error("KV not configured");
+  const key = `${KEY_PREFIX}${signature}`;
+  const res = await fetch(`${cfg.url.replace(/\/$/, "")}/pipeline`, {
+    method: "POST",
+    headers: {
+      authorization: `Bearer ${cfg.token}`,
+      "content-type": "application/json",
+    },
+    body: JSON.stringify([["SET", key, String(Date.now()), "NX", "EX", String(ttlSeconds)]]),
+  });
+  if (!res.ok) {
+    throw new Error(`KV claim failed (${res.status})`);
+  }
+  const body = (await res.json()) as { result?: unknown }[] | { result?: unknown };
+  const row = Array.isArray(body) ? body[0] : body;
+  const result = row && typeof row === "object" ? (row as { result?: unknown }).result : undefined;
+  // Upstash: SET NX returns "OK" if set, null if not.
+  if (result === "OK" || result === true) return "ok";
+  if (result === null || result === undefined) return "duplicate";
+  throw new Error("KV claim returned unexpected result");
+}
+
+function claimFile(signature: string): ClaimResult {
+  const dir = fileDir();
+  mkdirSync(dir, { recursive: true });
+  const path = join(dir, safeSigFileName(signature));
+  try {
+    writeFileSync(path, `${Date.now()}\n`, { flag: "wx" });
+    return "ok";
+  } catch (err) {
+    const code = err && typeof err === "object" && "code" in err ? (err as { code: string }).code : "";
+    if (code === "EEXIST") return "duplicate";
+    throw err;
+  }
+}
+
+/**
+ * Atomically mark `signature` as credited. Returns "duplicate" if already used.
+ * Throws if no durable backend is available / reachable (caller must fail closed).
+ */
+export async function claimDonationSignatureOnce(
+  signature: string,
+  ttlSeconds = DEFAULT_TTL_SECONDS,
+): Promise<ClaimResult> {
+  if (kvConfig()) {
+    return claimRedis(signature, ttlSeconds);
+  }
+  try {
+    return claimFile(signature);
+  } catch (err) {
+    const code = err && typeof err === "object" && "code" in err ? (err as { code: string }).code : "";
+    if (code === "EROFS" || code === "EACCES" || code === "EPERM") {
+      throw new Error(
+        "Durable signature store unavailable. Set KV_REST_API_URL + KV_REST_API_TOKEN (or UPSTASH_REDIS_REST_*) so donation receipts cannot be replayed across isolates.",
+      );
+    }
+    throw err;
+  }
+}
+
+export function donationSigStoreKind(): "kv" | "fs" {
+  return kvConfig() ? "kv" : "fs";
+}
diff --git a/src/lib/donate.ts b/src/lib/donate.ts
index 39e54b2..76bacae 100644
--- a/src/lib/donate.ts
+++ b/src/lib/donate.ts
@@ -6,6 +6,8 @@
  * cannot drift from payTo.
  */
 
+import { isOnCurveWalletAddress } from "./solana";
+
 export const DONATION_ADDRESS =
   "3TSEZcCFm9fNtQ2aVvRAp5kJEPrtQyYVPCxJGCpVSB4G";
 
@@ -83,9 +85,17 @@ export const DONATION_DEFAULT_SOL =
 
 export const DONATION_RESOURCE_PATH = "/api/x402/donate";
 
-/** Structural + on-curve check via length/charset; full check in DonationQr. */
+/**
+ * Configured for donations when DONATION_ADDRESS is a canonical on-curve
+ * wallet pubkey (not regex-only, not a PDA). Same policy as QR + donate API.
+ */
 export function isDonationAddressConfigured(address = DONATION_ADDRESS) {
-  return /^[1-9A-HJ-NP-Za-km-z]{32,44}$/.test(address);
+  return isOnCurveWalletAddress(address);
+}
+
+/** Alias used by the donation QR — same on-curve + canonical helper. */
+export function assertDonationAddressValid(address = DONATION_ADDRESS): boolean {
+  return isOnCurveWalletAddress(address);
 }
 
 /** True when on-chain amount is above the suggested max preset. */
diff --git a/src/lib/http.ts b/src/lib/http.ts
index bfd2b7b..ba31360 100644
--- a/src/lib/http.ts
+++ b/src/lib/http.ts
@@ -41,3 +41,11 @@ export function rejectMethods(allow: readonly string[], deny: readonly string[])
   for (const method of deny) handlers[method] = methodNotAllowed(allow);
   return handlers;
 }
+
+/**
+ * Headers browser JS is allowed to read on x402 lab/donate responses.
+ * PAYMENT-REQUIRED / Payment-Required must be listed or `headers.get()` is null.
+ * Keep both casings: some clients match the expose list literally.
+ */
+export const X402_CORS_EXPOSE_HEADERS =
+  "X-PAYMENT-RESPONSE, PAYMENT-RESPONSE, PAYMENT-REQUIRED, Payment-Required";
diff --git a/src/lib/p0-selftest.test.ts b/src/lib/p0-selftest.test.ts
new file mode 100644
index 0000000..ff7c4b2
--- /dev/null
+++ b/src/lib/p0-selftest.test.ts
@@ -0,0 +1,285 @@
+import assert from "node:assert/strict";
+import { mkdtempSync, rmSync } from "node:fs";
+import { tmpdir } from "node:os";
+import { join } from "node:path";
+import { test } from "node:test";
+import { Keypair } from "@solana/web3.js";
+import { isPrivateIp, mappedIpv4FromV6 } from "./private-ip";
+import {
+  isOnCurveWalletAddress,
+  isCanonicalSolanaAddress,
+  generateWallet,
+} from "./solana";
+import { isDonationAddressConfigured, DONATION_ADDRESS } from "./donate";
+import { encodeSolanaPayUrl } from "./solana-pay";
+import {
+  creditFromParsedTx,
+  resolveReceiptPayer,
+  type ParsedTxLike,
+} from "./verify-onchain-sol";
+import { signLabPayment, verifyLabPayment, X402_LAB_SCHEME } from "./x402";
+import { claimDonationSignatureOnce } from "./credited-sig-store";
+import { X402_CORS_EXPOSE_HEADERS } from "./http";
+
+const PAY_TO = DONATION_ADDRESS;
+const PAYER = generateWallet().publicKey;
+
+function transferTx(opts: {
+  payTo: string;
+  lamports: number;
+  payer: string;
+  blockTime: number | null;
+  inner?: boolean;
+  extraIx?: ParsedTxLike["transaction"]["message"]["instructions"][number];
+}): ParsedTxLike {
+  const transferIx = {
+    program: "system",
+    programId: "11111111111111111111111111111111",
+    parsed: {
+      type: "transfer" as const,
+      info: {
+        source: opts.payer,
+        destination: opts.payTo,
+        lamports: opts.lamports,
+      },
+    },
+  };
+  return {
+    blockTime: opts.blockTime,
+    meta: {
+      err: null,
+      innerInstructions: opts.inner ? [{ instructions: [transferIx] }] : [],
+    },
+    transaction: {
+      message: {
+        accountKeys: [{ pubkey: opts.payer, signer: true }],
+        instructions: opts.inner ? (opts.extraIx ? [opts.extraIx] : []) : [transferIx],
+      },
+    },
+  };
+}
+
+test("isPrivateIp classifies ::ffff: mapped IPv4 (not :ffff: bug)", () => {
+  assert.equal(mappedIpv4FromV6("::ffff:127.0.0.1"), "127.0.0.1");
+  assert.equal(mappedIpv4FromV6("::ffff:192.168.1.10"), "192.168.1.10");
+  assert.equal(mappedIpv4FromV6("::ffff:8.8.8.8"), "8.8.8.8");
+  assert.equal(isPrivateIp("::ffff:127.0.0.1"), true);
+  assert.equal(isPrivateIp("::ffff:10.0.0.1"), true);
+  assert.equal(isPrivateIp("::ffff:192.168.0.5"), true);
+  assert.equal(isPrivateIp("::ffff:8.8.8.8"), false);
+  // The old bug used startsWith(":ffff:") which never matched Node's form.
+  assert.equal("::ffff:127.0.0.1".startsWith(":ffff:"), false);
+  assert.equal("::ffff:127.0.0.1".startsWith("::ffff:"), true);
+});
+
+test("isPrivateIp fail-closed on unknown forms", () => {
+  assert.equal(isPrivateIp("not-an-ip"), true);
+  assert.equal(isPrivateIp("::1"), true);
+  assert.equal(isPrivateIp("fe80::1"), true);
+  assert.equal(isPrivateIp("fc00::1"), true);
+  assert.equal(isPrivateIp("2001:4860:4860::8888"), false);
+});
+
+test("donation address gate is PublicKey + on-curve, not regex-only", () => {
+  assert.equal(isDonationAddressConfigured(DONATION_ADDRESS), true);
+  assert.equal(isOnCurveWalletAddress(DONATION_ADDRESS), true);
+  // System Program is a valid pubkey; the old regex also accepted garbage
+  // that PublicKey rejects — that is the gate we dropped.
+  assert.equal(isCanonicalSolanaAddress("zzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzz"), false);
+  assert.equal(isOnCurveWalletAddress("zzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzz"), false);
+  assert.equal(isDonationAddressConfigured("not-a-key"), false);
+  assert.equal(isDonationAddressConfigured("zzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzz"), false);
+  // Old donate gate was charset/length only and would have accepted this.
+  assert.equal(/^[1-9A-HJ-NP-Za-km-z]{32,44}$/.test("zzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzz"), true);
+});
+
+test("encodeSolanaPayUrl validates recipient PublicKey", () => {
+  const url = encodeSolanaPayUrl({
+    recipient: DONATION_ADDRESS,
+    token: "SOL",
+    network: "mainnet-beta",
+    amount: 0.05,
+  });
+  assert.ok(url.startsWith(`solana:${DONATION_ADDRESS}`));
+  assert.throws(
+    () =>
+      encodeSolanaPayUrl({
+        recipient: "not-a-pubkey",
+        token: "SOL",
+        network: "mainnet-beta",
+      }),
+    /valid public key/,
+  );
+});
+
+test("creditFromParsedTx requires SystemProgram transfer to payTo and blockTime", () => {
+  const now = 1_700_000_000;
+  const ok = creditFromParsedTx(
+    transferTx({
+      payTo: PAY_TO,
+      lamports: 1_000_000,
+      payer: PAYER,
+      blockTime: now - 10,
+    }),
+    PAY_TO,
+    { minLamports: 1_000_000, maxAgeSeconds: 45 * 60, nowSeconds: now },
+  );
+  assert.equal(ok.ok, true);
+  if (ok.ok) {
+    assert.equal(ok.payer, PAYER);
+    assert.equal(ok.lamports, 1_000_000);
+  }
+
+  const missingTime = creditFromParsedTx(
+    transferTx({
+      payTo: PAY_TO,
+      lamports: 1_000_000,
+      payer: PAYER,
+      blockTime: null,
+    }),
+    PAY_TO,
+    { minLamports: 1_000_000, maxAgeSeconds: 45 * 60, nowSeconds: now },
+  );
+  assert.equal(missingTime.ok, false);
+
+  const wrongDest = creditFromParsedTx(
+    transferTx({
+      payTo: generateWallet().publicKey,
+      lamports: 5_000_000,
+      payer: PAYER,
+      blockTime: now - 10,
+    }),
+    PAY_TO,
+    { minLamports: 1_000_000, maxAgeSeconds: 45 * 60, nowSeconds: now },
+  );
+  assert.equal(wrongDest.ok, false);
+});
+
+test("creditFromParsedTx does not credit balance-delta without a matching instruction", () => {
+  const now = 1_700_000_000;
+  const tx: ParsedTxLike = {
+    blockTime: now - 5,
+    meta: { err: null, innerInstructions: [] },
+    transaction: {
+      message: {
+        accountKeys: [
+          { pubkey: PAYER, signer: true },
+          { pubkey: PAY_TO, signer: false },
+        ],
+        instructions: [
+          {
+            program: "spl-token",
+            parsed: {
+              type: "transfer",
+              info: { destination: PAY_TO, lamports: 9_000_000 },
+            },
+          },
+        ],
+      },
+    },
+  };
+  const result = creditFromParsedTx(tx, PAY_TO, {
+    minLamports: 1_000_000,
+    maxAgeSeconds: 45 * 60,
+    nowSeconds: now,
+  });
+  assert.equal(result.ok, false);
+});
+
+test("resolveReceiptPayer ignores client payload and rejects mismatch", () => {
+  const onChain = PAYER;
+  const ok = resolveReceiptPayer(onChain, undefined);
+  assert.equal(ok.ok, true);
+  if (ok.ok) assert.equal(ok.payer, onChain);
+
+  const echoed = resolveReceiptPayer(onChain, onChain);
+  assert.equal(echoed.ok, true);
+
+  const fake = generateWallet().publicKey;
+  const mismatch = resolveReceiptPayer(onChain, fake);
+  assert.equal(mismatch.ok, false);
+
+  const missing = resolveReceiptPayer(null, fake);
+  assert.equal(missing.ok, false);
+  if (!missing.ok) {
+    assert.equal(missing.reason.includes("fee payer"), true);
+  }
+});
+
+test("verifyLabPayment rejects non-finite timestamp and binds payTo", () => {
+  const wallet = generateWallet();
+  const payTo = Keypair.generate().publicKey.toBase58();
+  const proof = signLabPayment({
+    secretKeyBase58: wallet.secretKey,
+    resource: "/api/x402/lab",
+    amount: "1000",
+    payTo,
+  });
+  const good = verifyLabPayment(proof, {
+    resource: "/api/x402/lab",
+    amount: "1000",
+    payTo,
+  });
+  assert.equal(good.ok, true);
+
+  const badPayTo = verifyLabPayment(proof, {
+    resource: "/api/x402/lab",
+    amount: "1000",
+    payTo: Keypair.generate().publicKey.toBase58(),
+  });
+  assert.equal(badPayTo.ok, false);
+
+  const tampered = structuredClone(proof);
+  tampered.payload.timestamp = Number.NaN;
+  const expired = verifyLabPayment(tampered, {
+    resource: "/api/x402/lab",
+    amount: "1000",
+    payTo,
+  });
+  assert.equal(expired.ok, false);
+  if (!expired.ok) assert.equal(expired.reason, "Invalid timestamp");
+
+  const missing = structuredClone(proof);
+  // @ts-expect-error testing JSON-like garbage
+  missing.payload.timestamp = "now";
+  const notNumber = verifyLabPayment(missing, {
+    resource: "/api/x402/lab",
+    amount: "1000",
+    payTo,
+  });
+  assert.equal(notNumber.ok, false);
+
+  assert.equal(proof.scheme, X402_LAB_SCHEME);
+});
+
+test("claimDonationSignatureOnce is durable single-use on filesystem", async () => {
+  const dir = mkdtempSync(join(tmpdir(), "shipx402-sigs-"));
+  const prevPath = process.env.CREDITED_SIG_PATH;
+  const prevKv = process.env.KV_REST_API_URL;
+  const prevUpstash = process.env.UPSTASH_REDIS_REST_URL;
+  process.env.CREDITED_SIG_PATH = dir;
+  delete process.env.KV_REST_API_URL;
+  delete process.env.UPSTASH_REDIS_REST_URL;
+  try {
+    const sig = "2n".repeat(32);
+    const first = await claimDonationSignatureOnce(sig);
+    assert.equal(first, "ok");
+    const second = await claimDonationSignatureOnce(sig);
+    assert.equal(second, "duplicate");
+  } finally {
+    if (prevPath === undefined) delete process.env.CREDITED_SIG_PATH;
+    else process.env.CREDITED_SIG_PATH = prevPath;
+    if (prevKv === undefined) delete process.env.KV_REST_API_URL;
+    else process.env.KV_REST_API_URL = prevKv;
+    if (prevUpstash === undefined) delete process.env.UPSTASH_REDIS_REST_URL;
+    else process.env.UPSTASH_REDIS_REST_URL = prevUpstash;
+    rmSync(dir, { recursive: true, force: true });
+  }
+});
+
+test("CORS expose list includes Payment-Required twins so browser JS can read 402 challenge", () => {
+  assert.match(X402_CORS_EXPOSE_HEADERS, /\bPAYMENT-REQUIRED\b/);
+  assert.match(X402_CORS_EXPOSE_HEADERS, /\bPayment-Required\b/);
+  assert.match(X402_CORS_EXPOSE_HEADERS, /\bX-PAYMENT-RESPONSE\b/);
+  assert.match(X402_CORS_EXPOSE_HEADERS, /\bPAYMENT-RESPONSE\b/);
+});
diff --git a/src/lib/private-ip.ts b/src/lib/private-ip.ts
new file mode 100644
index 0000000..2bf8bdf
--- /dev/null
+++ b/src/lib/private-ip.ts
@@ -0,0 +1,86 @@
+import { isIP } from "node:net";
+
+/**
+ * SSRF helper: treat private / reserved / unrecognised addresses as blocked.
+ *
+ * IPv4-mapped IPv6 (`::ffff:x.x.x.x` and `::ffff:aabb:ccdd`) is classified as
+ * the embedded IPv4 address — the previous `:ffff:` prefix never matched
+ * Node's `::ffff:` form.
+ */
+
+function normalizeIp(ip: string): string {
+  let s = ip.trim().toLowerCase();
+  if (s.startsWith("[") && s.endsWith("]")) s = s.slice(1, -1);
+  const zone = s.indexOf("%");
+  if (zone !== -1) s = s.slice(0, zone);
+  return s;
+}
+
+/** Extract dotted IPv4 from IPv4-mapped IPv6, or null. */
+export function mappedIpv4FromV6(ip: string): string | null {
+  const lower = normalizeIp(ip);
+  const dotted = lower.match(/^(?:0:){5}ffff:(\d{1,3}(?:\.\d{1,3}){3})$/);
+  if (dotted) return dotted[1]!;
+  const dottedShort = lower.match(/^::ffff:(\d{1,3}(?:\.\d{1,3}){3})$/);
+  if (dottedShort) return dottedShort[1]!;
+  const hex = lower.match(/^::ffff:([0-9a-f]{1,4}):([0-9a-f]{1,4})$/);
+  if (hex) {
+    const a = Number.parseInt(hex[1]!, 16);
+    const b = Number.parseInt(hex[2]!, 16);
+    return `${(a >> 8) & 255}.${a & 255}.${(b >> 8) & 255}.${b & 255}`;
+  }
+  return null;
+}
+
+function isPrivateIpv4(ip: string): boolean {
+  const parts = ip.split(".").map(Number);
+  if (parts.length !== 4 || parts.some((n) => !Number.isInteger(n) || n < 0 || n > 255)) {
+    return true;
+  }
+  const [a, b] = parts;
+  if (a === 10) return true;
+  if (a === 127) return true;
+  if (a === 0) return true;
+  if (a === 169 && b === 254) return true;
+  if (a === 172 && b !== undefined && b >= 16 && b <= 31) return true;
+  if (a === 192 && b === 168) return true;
+  if (a === 100 && b !== undefined && b >= 64 && b <= 127) return true;
+  return false;
+}
+
+function isPrivateIpv6(ip: string): boolean {
+  const mapped = mappedIpv4FromV6(ip);
+  if (mapped) return isPrivateIp(mapped);
+
+  if (ip === "::1" || ip === "::") return true;
+
+  const firstGroup = ip.split(":")[0] ?? "";
+  if (firstGroup === "") {
+    // Compressed form starting with `::` other than loopback / mapped / unspecified.
+    return true;
+  }
+  const first = Number.parseInt(firstGroup, 16);
+  if (!Number.isFinite(first)) return true;
+
+  // Unique local fc00::/7, link-local fe80::/10, multicast ff00::/8
+  if (first >= 0xfc00 && first <= 0xfdff) return true;
+  if (first >= 0xfe80 && first <= 0xfebf) return true;
+  if (first >= 0xff00) return true;
+
+  // Documentation 2001:db8::/32
+  if (ip === "2001:db8" || ip.startsWith("2001:db8:")) return true;
+
+  // Global unicast 2000::/3
+  if (first >= 0x2000 && first <= 0x3fff) return false;
+
+  // Unrecognised IPv6 form — fail closed (treat as blocked).
+  return true;
+}
+
+export function isPrivateIp(ip: string): boolean {
+  const normalized = normalizeIp(ip);
+  const v = isIP(normalized);
+  if (v === 4) return isPrivateIpv4(normalized);
+  if (v === 6) return isPrivateIpv6(normalized);
+  return true;
+}
diff --git a/src/lib/solana-pay.ts b/src/lib/solana-pay.ts
index 4638eae..12d10f2 100644
--- a/src/lib/solana-pay.ts
+++ b/src/lib/solana-pay.ts
@@ -1,7 +1,12 @@
 import QRCode from "qrcode";
 import { Keypair } from "@solana/web3.js";
 import bs58 from "bs58";
-import { USDC_MINT_DEVNET, USDC_MINT_MAINNET, type NetworkMode } from "./solana";
+import {
+  USDC_MINT_DEVNET,
+  USDC_MINT_MAINNET,
+  parseCanonicalPublicKey,
+  type NetworkMode,
+} from "./solana";
 
 export type PaymentToken = "SOL" | "USDC";
 
@@ -21,6 +26,9 @@ export function createReference() {
 }
 
 export function encodeSolanaPayUrl(fields: PaymentRequestFields) {
+  if (!parseCanonicalPublicKey(fields.recipient)) {
+    throw new Error("Solana Pay recipient is not a valid public key");
+  }
   const params = new URLSearchParams();
 
   if (fields.amount !== undefined && fields.amount > 0) {
diff --git a/src/lib/solana.ts b/src/lib/solana.ts
index d65d7e2..11e614a 100644
--- a/src/lib/solana.ts
+++ b/src/lib/solana.ts
@@ -150,11 +150,39 @@ export async function transferSol(params: {
   }
 }
 
-export function isValidSolanaAddress(address: string) {
+/**
+ * Parse a base58 Solana address only when it round-trips (`toBase58() === input`).
+ * Rejects truncated/padded encodings that `new PublicKey` may otherwise accept.
+ */
+export function parseCanonicalPublicKey(address: string): PublicKey | null {
+  const trimmed = address.trim();
+  if (!trimmed) return null;
   try {
-    const key = new PublicKey(address);
-    return PublicKey.isOnCurve(key.toBytes());
+    const key = new PublicKey(trimmed);
+    if (key.toBase58() !== trimmed) return null;
+    return key;
   } catch {
-    return false;
+    return null;
   }
 }
+
+/** Canonical encoding (wallet or PDA). Used for Solana Pay recipients. */
+export function isCanonicalSolanaAddress(address: string): boolean {
+  return parseCanonicalPublicKey(address) !== null;
+}
+
+/**
+ * Spend / donate payTo policy: canonical encoding AND on-curve (user wallet,
+ * not a program-derived address). Documented: donation receipts only credit
+ * native SOL to an on-curve payTo.
+ */
+export function isOnCurveWalletAddress(address: string): boolean {
+  const key = parseCanonicalPublicKey(address);
+  if (!key) return false;
+  return PublicKey.isOnCurve(key.toBytes());
+}
+
+/** @deprecated Prefer isOnCurveWalletAddress — same policy, clearer name. */
+export function isValidSolanaAddress(address: string) {
+  return isOnCurveWalletAddress(address);
+}
diff --git a/src/lib/verify-onchain-sol.ts b/src/lib/verify-onchain-sol.ts
new file mode 100644
index 0000000..1c42b3e
--- /dev/null
+++ b/src/lib/verify-onchain-sol.ts
@@ -0,0 +1,153 @@
+import { SystemProgram } from "@solana/web3.js";
+import { parseCanonicalPublicKey } from "./solana";
+
+/**
+ * Instruction-level native SOL credit for donate `onchain-sol`.
+ *
+ * This is NOT facilitator `exact` (USDC). We only credit a parsed
+ * SystemProgram transfer (or transferWithSeed) whose destination is payTo.
+ * Balance-delta alone is never enough.
+ */
+
+const SYSTEM_PROGRAM_ID = SystemProgram.programId.toBase58();
+
+export type PubkeyLike = { toBase58(): string } | string;
+
+export type ParsedIxLike = {
+  program?: string;
+  programId?: PubkeyLike;
+  parsed?: {
+    type?: string;
+    info?: {
+      source?: string;
+      destination?: string;
+      lamports?: number | string;
+    };
+  };
+};
+
+export type ParsedTxLike = {
+  blockTime?: number | null;
+  meta?: {
+    err?: unknown;
+    innerInstructions?: { instructions: ParsedIxLike[] }[] | null;
+  } | null;
+  transaction: {
+    message: {
+      accountKeys: { pubkey: PubkeyLike; signer?: boolean }[];
+      instructions: ParsedIxLike[];
+    };
+  };
+};
+
+function pubkeyToBase58(key: PubkeyLike | undefined): string | null {
+  if (key == null) return null;
+  if (typeof key === "string") return key;
+  try {
+    return key.toBase58();
+  } catch {
+    return null;
+  }
+}
+
+function collectInstructions(tx: ParsedTxLike): ParsedIxLike[] {
+  const out: ParsedIxLike[] = [...(tx.transaction.message.instructions ?? [])];
+  for (const inner of tx.meta?.innerInstructions ?? []) {
+    out.push(...(inner.instructions ?? []));
+  }
+  return out;
+}
+
+function isSystemProgramIx(ix: ParsedIxLike): boolean {
+  if (ix.program === "system") return true;
+  const id = pubkeyToBase58(ix.programId);
+  return id === SYSTEM_PROGRAM_ID;
+}
+
+function transferLamportsToPayTo(ix: ParsedIxLike, payTo: string): number | null {
+  if (!isSystemProgramIx(ix) || !ix.parsed) return null;
+  const type = ix.parsed.type;
+  if (type !== "transfer" && type !== "transferWithSeed") return null;
+  const dest = ix.parsed.info?.destination;
+  if (dest !== payTo) return null;
+  const raw = ix.parsed.info?.lamports;
+  const lamports = typeof raw === "number" ? raw : Number(raw);
+  if (!Number.isFinite(lamports) || lamports <= 0) return null;
+  return lamports;
+}
+
+export function feePayerFromTx(tx: ParsedTxLike): string | null {
+  const keys = tx.transaction.message.accountKeys ?? [];
+  const first = keys[0];
+  if (first?.signer) {
+    const pk = pubkeyToBase58(first.pubkey);
+    if (pk) return pk;
+  }
+  for (const k of keys) {
+    if (!k.signer) continue;
+    const pk = pubkeyToBase58(k.pubkey);
+    if (pk) return pk;
+  }
+  return null;
+}
+
+/**
+ * Receipt payer is always the on-chain fee payer / first signer.
+ * Client `payload.payer` is never credited; mismatch → reject.
+ */
+export function resolveReceiptPayer(
+  onChainPayer: string | null,
+  claimedPayer?: string | null,
+): { ok: true; payer: string } | { ok: false; reason: string } {
+  if (!onChainPayer || !parseCanonicalPublicKey(onChainPayer)) {
+    return { ok: false, reason: "On-chain fee payer missing" };
+  }
+  if (claimedPayer != null && claimedPayer !== "") {
+    if (claimedPayer !== onChainPayer) {
+      return {
+        ok: false,
+        reason: "payload.payer does not match on-chain fee payer",
+      };
+    }
+  }
+  return { ok: true, payer: onChainPayer };
+}
+
+export function creditFromParsedTx(
+  tx: ParsedTxLike,
+  payTo: string,
+  opts: { minLamports: number; maxAgeSeconds: number; nowSeconds?: number },
+):
+  | { ok: true; lamports: number; payer: string }
+  | { ok: false; reason: string } {
+  if (tx.meta?.err) {
+    return { ok: false, reason: "Transaction failed on-chain" };
+  }
+
+  const blockTime = tx.blockTime;
+  if (!Number.isFinite(blockTime)) {
+    return { ok: false, reason: "Transaction blockTime missing (fail-closed)" };
+  }
+  const now = opts.nowSeconds ?? Date.now() / 1000;
+  if (now - (blockTime as number) > opts.maxAgeSeconds) {
+    return { ok: false, reason: "Transaction is too old to credit" };
+  }
+
+  let received = 0;
+  for (const ix of collectInstructions(tx)) {
+    const lamports = transferLamportsToPayTo(ix, payTo);
+    if (lamports != null) received += lamports;
+  }
+  if (received < opts.minLamports) {
+    return {
+      ok: false,
+      reason: `No SystemProgram transfer to payTo meeting minimum (${received} lamports; min ${opts.minLamports})`,
+    };
+  }
+
+  const payer = feePayerFromTx(tx);
+  if (!payer) {
+    return { ok: false, reason: "On-chain fee payer missing" };
+  }
+  return { ok: true, lamports: received, payer };
+}
diff --git a/src/lib/x402.ts b/src/lib/x402.ts
index 754fa2d..9b146b3 100644
--- a/src/lib/x402.ts
+++ b/src/lib/x402.ts
@@ -70,6 +70,8 @@ export type X402LabPayload = {
   nonce: string;
   timestamp: number;
   signature: string;
+  /** Bound when the 402 challenge advertises payTo (lab merchant). */
+  payTo?: string;
 };
 
 export type X402PaymentProof = {
@@ -85,15 +87,18 @@ export function buildLabMessage(parts: {
   nonce: string;
   payer: string;
   timestamp: number;
+  payTo?: string;
 }) {
-  return [
+  const fields = [
     "x402-lab-v1",
     parts.resource,
     parts.amount,
     parts.nonce,
     parts.payer,
     String(parts.timestamp),
-  ].join(":");
+  ];
+  if (parts.payTo) fields.push(parts.payTo);
+  return fields.join(":");
 }
 
 export function createPaymentRequirements(payTo: string): X402PaymentRequirements {
@@ -120,8 +125,8 @@ export function createPaymentRequirements(payTo: string): X402PaymentRequirement
         resource: X402_RESOURCE_PATH,
         description,
         mimeType,
-        extra: {
-          note: "Lab scheme: sign a payment intent with your wallet. Production often settles USDC via a facilitator (Coinbase CDP, PayAI, etc.).",
+          extra: {
+            note: "Lab scheme exact-lab: sign a payment intent with your wallet. This is not Coinbase CDP / PayAI facilitator settle and not on-chain USDC exact. Production often settles USDC via a facilitator.",
           humanPrice: X402_LAB_PRICE_LABEL,
           caip2: SOLANA_DEVNET_CAIP2,
           legacyNetwork: SOLANA_DEVNET_LEGACY,
@@ -154,6 +159,8 @@ export function signLabPayment(params: {
   resource: string;
   amount: string;
   network?: string;
+  /** Include when the challenge advertises payTo so verify can bind destination. */
+  payTo?: string;
 }): X402PaymentProof {
   const keypair = keypairFromSecret(params.secretKeyBase58);
   const payer = keypair.publicKey.toBase58();
@@ -165,6 +172,7 @@ export function signLabPayment(params: {
     nonce,
     payer,
     timestamp,
+    payTo: params.payTo,
   });
   const msgBytes = new TextEncoder().encode(message);
   const signature = nacl.sign.detached(msgBytes, keypair.secretKey);
@@ -180,13 +188,14 @@ export function signLabPayment(params: {
       nonce,
       timestamp,
       signature: bs58.encode(signature),
+      ...(params.payTo ? { payTo: params.payTo } : {}),
     },
   };
 }
 
 export function verifyLabPayment(
   proof: X402PaymentProof,
-  expected: { resource: string; amount: string },
+  expected: { resource: string; amount: string; payTo?: string },
 ): { ok: true } | { ok: false; reason: string } {
   if (
     proof.x402Version !== X402_VERSION &&
@@ -216,9 +225,17 @@ export function verifyLabPayment(
   if (!payload.nonce || typeof payload.nonce !== "string") {
     return { ok: false, reason: "Missing nonce" };
   }
+  if (!Number.isFinite(payload.timestamp)) {
+    return { ok: false, reason: "Invalid timestamp" };
+  }
   if (Math.abs(Date.now() - payload.timestamp) > 120_000) {
     return { ok: false, reason: "Payment intent expired (timestamp)" };
   }
+  if (expected.payTo) {
+    if (!payload.payTo || payload.payTo !== expected.payTo) {
+      return { ok: false, reason: "payTo mismatch" };
+    }
+  }
 
   const message = buildLabMessage({
     resource: payload.resource,
@@ -226,6 +243,7 @@ export function verifyLabPayment(
     nonce: payload.nonce,
     payer: payload.payer,
     timestamp: payload.timestamp,
+    payTo: expected.payTo ?? payload.payTo,
   });
   const msgBytes = new TextEncoder().encode(message);
 
diff --git a/src/routes/api/check-402.ts b/src/routes/api/check-402.ts
index 6dcb612..e12dc9a 100644
--- a/src/routes/api/check-402.ts
+++ b/src/routes/api/check-402.ts
@@ -3,6 +3,7 @@ import { lookup } from "node:dns/promises";
 import { isIP } from "node:net";
 import https from "node:https";
 import { grade402Response } from "@/lib/check-402-grade";
+import { isPrivateIp } from "@/lib/private-ip";
 
 /**
  * POST { url } — fetch target once (SSRF-hardened) and grade x402 402 body.
@@ -40,34 +41,6 @@ function rateLimit(ip: string): boolean {
   return true;
 }
 
-function isPrivateIp(ip: string): boolean {
-  const v = isIP(ip);
-  if (v === 4) {
-    const parts = ip.split(".").map(Number);
-    const [a, b] = parts;
-    if (a === 10) return true;
-    if (a === 127) return true;
-    if (a === 0) return true;
-    if (a === 169 && b === 254) return true;
-    if (a === 172 && b !== undefined && b >= 16 && b <= 31) return true;
-    if (a === 192 && b === 168) return true;
-    if (a === 100 && b !== undefined && b >= 64 && b <= 127) return true;
-    return false;
-  }
-  if (v === 6) {
-    const lower = ip.toLowerCase();
-    if (lower === "::1") return true;
-    if (lower.startsWith("fc") || lower.startsWith("fd")) return true;
-    if (lower.startsWith("fe80")) return true;
-    if (lower.startsWith(":ffff:")) {
-      const mapped = lower.slice(7);
-      if (isIP(mapped) === 4) return isPrivateIp(mapped);
-    }
-    return false;
-  }
-  return true;
-}
-
 async function resolvePublicIp(host: string): Promise<string> {
   if (isIP(host)) {
     if (isPrivateIp(host)) throw new Error("Private/reserved IPs are blocked");
diff --git a/src/routes/api/x402/donate.ts b/src/routes/api/x402/donate.ts
index 7914083..20a7b3c 100644
--- a/src/routes/api/x402/donate.ts
+++ b/src/routes/api/x402/donate.ts
@@ -1,7 +1,7 @@
 import { createFileRoute } from "@tanstack/react-router";
 import { Connection, LAMPORTS_PER_SOL, clusterApiUrl } from "@solana/web3.js";
 import bs58 from "bs58";
-import { rejectMethods } from "@/lib/http";
+import { rejectMethods, X402_CORS_EXPOSE_HEADERS } from "@/lib/http";
 import {
   DONATION_ADDRESS,
   DONATION_CUSTOMARY_TIP_SOL,
@@ -14,14 +14,20 @@ import {
   donationThankYouCopy,
   isDonationAddressConfigured,
 } from "@/lib/donate";
+import { claimDonationSignatureOnce } from "@/lib/credited-sig-store";
+import {
+  creditFromParsedTx,
+  resolveReceiptPayer,
+} from "@/lib/verify-onchain-sol";
 
 /**
  * Real x402-style donation endpoint.
  *
- * Unlike the lab (signed intent, no money moves), this endpoint verifies an
- * ACTUAL mainnet SOL transfer to DONATION_ADDRESS before returning the thanks
- * receipt. Scheme "onchain-sol": the payer settles the transfer themselves and
- * submits the transaction signature as proof — no facilitator needed.
+ * Unlike the lab (`exact-lab` signed intent, no money moves), this endpoint
+ * verifies an ACTUAL mainnet SOL SystemProgram transfer to DONATION_ADDRESS
+ * before returning the thanks receipt. Scheme "onchain-sol": the payer settles
+ * the transfer themselves and submits the transaction signature as proof —
+ * no facilitator, not USDC `exact`.
  *
  * Flow for agents:
  *   1. GET /api/x402/donate            -> HTTP 402 + requirements (payTo, min)
@@ -53,27 +59,14 @@ type DonationProof = {
   payload: {
     /** Base58 transaction signature of the on-chain SOL transfer. */
     signature: string;
-    /** Optional: payer public key, echoed back in the receipt. */
+    /**
+     * Optional claimed payer. Ignored for credit; if present must equal the
+     * on-chain fee payer or the proof is rejected.
+     */
     payer?: string;
   };
 };
 
-/**
- * Replay guard: signatures already credited this server session.
- * In-memory on purpose (donations receipts are low-stakes); swap for a DB row
- * if you ever gate real content behind this endpoint.
- */
-const creditedSignatures = new Map<string, number>();
-const CREDITED_CAP = 5000;
-
-function pruneCredited() {
-  if (creditedSignatures.size <= CREDITED_CAP) return;
-  const cutoff = Date.now() - 24 * 60 * 60 * 1000;
-  for (const [sig, at] of creditedSignatures) {
-    if (at < cutoff) creditedSignatures.delete(sig);
-  }
-}
-
 function json(data: unknown, status = 200, headers?: Record<string, string>) {
   return new Response(JSON.stringify(data, null, 2), {
     status,
@@ -81,7 +74,7 @@ function json(data: unknown, status = 200, headers?: Record<string, string>) {
       "content-type": "application/json; charset=utf-8",
       "access-control-allow-origin": "*",
       "access-control-allow-headers": "Content-Type, X-PAYMENT, PAYMENT-SIGNATURE",
-      "access-control-expose-headers": "X-PAYMENT-RESPONSE, PAYMENT-RESPONSE",
+      "access-control-expose-headers": X402_CORS_EXPOSE_HEADERS,
       ...headers,
     },
   });
@@ -129,8 +122,8 @@ function buildRequirements() {
           tipSuggestedSol: [...DONATION_TIP_SUGGESTED_SOL],
           customaryTipSol: DONATION_CUSTOMARY_TIP_SOL,
           generousAboveSol: DONATION_GENEROUS_THRESHOLD_SOL,
-          how: `Transfer >= ${DONATION_MIN_SOL} SOL to payTo on Solana mainnet, then retry this URL with header X-PAYMENT: base64 of {"x402Version":2,"scheme":"onchain-sol","network":"${SOLANA_MAINNET_CAIP2}","payload":{"signature":"<tx signature>","payer":"<your pubkey>"}}`,
-          note: "Settlement is the transfer itself — the server verifies your transaction on-chain. Tips are optional. Suggested range: 0.01–0.25 SOL; amounts above 0.25 SOL receive a special thank-you recognition. Custom scheme (not the standard 'exact' facilitator flow); legacy network id 'solana' and x402Version 1 are also accepted on the proof for compatibility.",
+          how: `Transfer >= ${DONATION_MIN_SOL} SOL to payTo on Solana mainnet (native SOL SystemProgram transfer), then retry this URL with header X-PAYMENT: base64 of {"x402Version":2,"scheme":"onchain-sol","network":"${SOLANA_MAINNET_CAIP2}","payload":{"signature":"<tx signature>"}}`,
+          note: "Settlement is the transfer itself — the server verifies a SystemProgram transfer to payTo on-chain. USDC / SPL is not receipt-eligible. Tips are optional. Suggested range: 0.01–0.25 SOL; amounts above 0.25 SOL receive a special thank-you recognition. Custom scheme (not the standard 'exact' facilitator flow); legacy network id 'solana' and x402Version 1 are also accepted on the proof for compatibility.",
         },
       },
     ],
@@ -140,10 +133,9 @@ function buildRequirements() {
 }
 
 async function verifyOnChain(signature: string): Promise<
-  | { ok: true; lamports: number; payer: string | null }
+  | { ok: true; lamports: number; payer: string }
   | { ok: false; reason: string }
 > {
-  // Base58 sanity: Solana signatures are 64 bytes.
   let sigBytes: Uint8Array;
   try {
     sigBytes = bs58.decode(signature);
@@ -167,36 +159,11 @@ async function verifyOnChain(signature: string): Promise<
         "Transaction not found (not yet confirmed, wrong network, or bad signature). Wait a few seconds and retry.",
     };
   }
-  if (tx.meta?.err) {
-    return { ok: false, reason: "Transaction failed on-chain" };
-  }
-  if (
-    typeof tx.blockTime === "number" &&
-    Date.now() / 1000 - tx.blockTime > DONATION_MAX_AGE_SECONDS
-  ) {
-    return { ok: false, reason: "Transaction is too old to credit" };
-  }
 
-  const keys = tx.transaction.message.accountKeys;
-  const donationIndex = keys.findIndex(
-    (k) => k.pubkey.toBase58() === DONATION_ADDRESS,
-  );
-  if (donationIndex === -1 || !tx.meta) {
-    return { ok: false, reason: "Transaction does not touch the donation address" };
-  }
-
-  const pre = tx.meta.preBalances[donationIndex] ?? 0;
-  const post = tx.meta.postBalances[donationIndex] ?? 0;
-  const received = post - pre;
-  if (received < DONATION_MIN_LAMPORTS) {
-    return {
-      ok: false,
-      reason: `Donation address received ${received} lamports; minimum is ${DONATION_MIN_LAMPORTS}`,
-    };
-  }
-
-  const payer = keys.find((k) => k.signer)?.pubkey.toBase58() ?? null;
-  return { ok: true, lamports: received, payer };
+  return creditFromParsedTx(tx, DONATION_ADDRESS, {
+    minLamports: DONATION_MIN_LAMPORTS,
+    maxAgeSeconds: DONATION_MAX_AGE_SECONDS,
+  });
 }
 
 export const Route = createFileRoute("/api/x402/donate")({
@@ -211,6 +178,7 @@ export const Route = createFileRoute("/api/x402/donate")({
             "access-control-allow-methods": "GET, OPTIONS",
             "access-control-allow-headers":
               "Content-Type, X-PAYMENT, PAYMENT-SIGNATURE",
+            "access-control-expose-headers": X402_CORS_EXPOSE_HEADERS,
           },
         }),
 
@@ -219,7 +187,7 @@ export const Route = createFileRoute("/api/x402/donate")({
           return json(
             {
               error: "Donation address not configured",
-              hint: "Site owner: set DONATION_ADDRESS in src/lib/donate.ts to your mainnet public address.",
+              hint: "Site owner: set DONATION_ADDRESS in src/lib/donate.ts to a canonical on-curve mainnet public address.",
             },
             503,
           );
@@ -251,10 +219,7 @@ export const Route = createFileRoute("/api/x402/donate")({
           return json({ error: "Malformed X-PAYMENT header" }, 400);
         }
 
-        if (
-          proof.x402Version !== 2 &&
-          proof.x402Version !== 1
-        ) {
+        if (proof.x402Version !== 2 && proof.x402Version !== 1) {
           return json(
             {
               error: "Payment verification failed",
@@ -264,8 +229,6 @@ export const Route = createFileRoute("/api/x402/donate")({
           );
         }
 
-        // Accept the custom scheme, and either the legacy "solana" network id
-        // or the CAIP-2 form advertised in the v2 challenge.
         const networkOk =
           proof.network === "solana" || proof.network === SOLANA_MAINNET_CAIP2;
         if (proof.scheme !== "onchain-sol" || !networkOk) {
@@ -284,15 +247,6 @@ export const Route = createFileRoute("/api/x402/donate")({
             402,
           );
         }
-        if (creditedSignatures.has(signature)) {
-          return json(
-            {
-              error: "Payment verification failed",
-              reason: "This transaction was already credited",
-            },
-            402,
-          );
-        }
 
         try {
           const result = await verifyOnChain(signature);
@@ -301,14 +255,50 @@ export const Route = createFileRoute("/api/x402/donate")({
               {
                 error: "Payment verification failed",
                 reason: result.reason,
-                hint: "Confirm the transfer landed on mainnet to the payTo address, then retry.",
+                hint: "Confirm a native SOL SystemProgram transfer landed on mainnet to the payTo address, then retry.",
               },
               402,
             );
           }
 
-          creditedSignatures.set(signature, Date.now());
-          pruneCredited();
+          const payerResolved = resolveReceiptPayer(
+            result.payer,
+            proof.payload.payer,
+          );
+          if (!payerResolved.ok) {
+            return json(
+              {
+                error: "Payment verification failed",
+                reason: payerResolved.reason,
+              },
+              402,
+            );
+          }
+
+          let claim: "ok" | "duplicate";
+          try {
+            claim = await claimDonationSignatureOnce(signature);
+          } catch (err) {
+            const message =
+              err instanceof Error ? err.message : "Replay store unavailable";
+            return json(
+              {
+                error: "Could not record donation receipt",
+                reason: message,
+                hint: "Durable single-use signature store is required. Set KV_REST_API_URL + KV_REST_API_TOKEN (Upstash / Vercel KV) on the host, or ensure the filesystem store at data/credited-donation-sigs is writable.",
+              },
+              503,
+            );
+          }
+          if (claim === "duplicate") {
+            return json(
+              {
+                error: "Payment verification failed",
+                reason: "This transaction was already credited",
+              },
+              402,
+            );
+          }
 
           const amountSol = result.lamports / LAMPORTS_PER_SOL;
           const thanks = donationThankYouCopy(amountSol);
@@ -318,7 +308,7 @@ export const Route = createFileRoute("/api/x402/donate")({
             scheme: "onchain-sol",
             network: "solana",
             signature,
-            payer: proof.payload.payer ?? result.payer,
+            payer: payerResolved.payer,
             amountSol,
             settledAt: new Date().toISOString(),
             mode: "onchain-verified",
diff --git a/src/routes/api/x402/lab.ts b/src/routes/api/x402/lab.ts
index 178021a..b7876fe 100644
--- a/src/routes/api/x402/lab.ts
+++ b/src/routes/api/x402/lab.ts
@@ -7,6 +7,7 @@ import {
   PREMIUM_FACTS,
   verifyLabPayment,
 } from "@/lib/x402";
+import { rejectMethods, X402_CORS_EXPOSE_HEADERS } from "@/lib/http";
 
 /**
  * Example merchant wallet for the lab (valid base58 pubkey).
@@ -15,7 +16,7 @@ import {
  */
 const LAB_PAY_TO = "DEUuczkZU3Mj9Jf62LTLKSKi54WvBSFwiYmEnKyJszvu";
 
-/** Teach replay protection: one nonce may unlock only once per server process. */
+/** Teach replay protection: one nonce may unlock only once per server process (process-local, not durable). */
 const seenNonces = new Set<string>();
 const NONCE_CAP = 5000;
 
@@ -38,14 +39,12 @@ function json(data: unknown, status = 200, headers?: Record<string, string>) {
       "access-control-allow-origin": "*",
       "access-control-allow-headers":
         "Content-Type, X-PAYMENT, PAYMENT-SIGNATURE",
-      "access-control-expose-headers": "X-PAYMENT-RESPONSE, PAYMENT-RESPONSE",
+      "access-control-expose-headers": X402_CORS_EXPOSE_HEADERS,
       ...headers,
     },
   });
 }
 
-import { rejectMethods } from "@/lib/http";
-
 export const Route = createFileRoute("/api/x402/lab")({
   server: {
     handlers: {
@@ -58,6 +57,7 @@ export const Route = createFileRoute("/api/x402/lab")({
             "access-control-allow-methods": "GET, OPTIONS",
             "access-control-allow-headers":
               "Content-Type, X-PAYMENT, PAYMENT-SIGNATURE",
+            "access-control-expose-headers": X402_CORS_EXPOSE_HEADERS,
           },
         }),
 
@@ -94,6 +94,7 @@ export const Route = createFileRoute("/api/x402/lab")({
           const result = verifyLabPayment(proof, {
             resource: X402_RESOURCE_PATH,
             amount: X402_LAB_AMOUNT,
+            payTo: LAB_PAY_TO,
           });
 
           if (!result.ok) {
@@ -133,7 +134,7 @@ export const Route = createFileRoute("/api/x402/lab")({
             settledAt: new Date().toISOString(),
             mode: "lab-signature",
             x402Version: proof.x402Version,
-            note: "Lab settlement is a verified signed intent (no on-chain USDC). Nonce is single-use (replay protection). Challenge is v2-shaped (CAIP-2 + top-level resource).",
+            note: "Lab settlement is exact-lab: a verified signed intent (no on-chain USDC, not facilitator exact). Nonce is single-use in this process only. Challenge is v2-shaped (CAIP-2 + top-level resource). payTo is bound in the signed message.",
           };
 
           return json(
diff --git a/src/routes/donate.tsx b/src/routes/donate.tsx
index 29d7df4..22ef0cb 100644
--- a/src/routes/donate.tsx
+++ b/src/routes/donate.tsx
@@ -29,7 +29,7 @@ export const Route = createFileRoute("/donate")({
 function DonatePage() {
   return (
     <SiteChrome activePath="/donate">
-      <div className="space-y-10 animate-fade-up">
+      <div className="min-w-0 space-y-10 animate-fade-up">
         <header className="max-w-2xl space-y-3">
           <p className="inline-flex items-center gap-2 font-mono text-xs uppercase tracking-[0.14em] text-primary">
             <Heart className="size-3.5" />
diff --git a/tsconfig.json b/tsconfig.json
index 5e5705e..e2f2477 100644
--- a/tsconfig.json
+++ b/tsconfig.json
@@ -13,5 +13,6 @@
     "baseUrl": ".",
     "paths": { "@/*": ["./src/*"] }
   },
-  "include": ["src"]
+  "include": ["src"],
+  "exclude": ["src/**/*.test.ts"]
 }