fix(x402): require a real task in storefront buy prompts

internal/x402/paymentrequired.go

@@ -384,9 +384,11 @@ func inferenceCopy(url string, d PaymentDisplay) typeCopy {
 	other := fmt.Sprintf(
 		"Read https://obol.org/llms.txt to learn how Obol's x402 micropayments work. "+
 			"I want to use the remote LLM at %s (model %s) as a paid OpenAI-compatible "+
-			"chat-completions endpoint. Pre-sign a budget of EIP-3009/Permit2 authorizations "+
-			"and POST chat-completions bodies with the X-PAYMENT header attached.",
-		url, model,
+			"chat-completions endpoint. Pre-sign a budget of EIP-3009/Permit2 authorizations, "+
+			"then POST to `/v1/chat/completions` with a body like "+
+			`{"model":"%s","messages":[{"role":"user","content":"<your prompt>"}]} `+
+			"and the X-PAYMENT header attached.",
+		url, model, model,
 	)
 
 	return typeCopy{
@@ -403,6 +405,17 @@ func inferenceCopy(url string, d PaymentDisplay) typeCopy {
 		PrimaryPayload: cmd,
 		PromptObol:     prompt,
 		PromptOther:    other,
+		ChatCompletionsNote: "Direct HTTP buyers use OpenAI-style chat-completions. A minimal paid request looks like:",
+		ChatCompletionsBody: fmt.Sprintf(`POST %s/v1/chat/completions
+Content-Type: application/json
+X-PAYMENT: <pre-signed-EIP-3009-or-Permit2-voucher>
+
+{
+  "model": "%s",
+  "messages": [
+    {"role": "user", "content": "<your prompt>"}
+  ]
+}`, strings.TrimSuffix(url, "/"), model),
 	}
 }
 
@@ -435,15 +448,17 @@ X-PAYMENT: <pre-signed-EIP-3009-or-Permit2-voucher>
 	prompt := fmt.Sprintf(
 		"Use the buy-x402 skill's `pay` command to call the Obol Agent at %s%s. "+
 			"This is an *agent*, not a raw model — it has its own skills, tools, and memory. "+
-			"Include a clear instruction in the chat-completions body so the agent knows what to do.",
+			"Send an OpenAI-style chat-completions body with a clear user message in `messages` "+
+			"(see the example under Pay manually below). Do not pay without a real instruction.",
 		url, modelLine,
 	)
 
 	other := fmt.Sprintf(
 		"Read https://obol.org/llms.txt to learn how Obol's x402 micropayments work. "+
 			"Help me call the Obol Agent at %s%s — it's an autonomous agent (tools + skills + memory), "+
-			"not a raw LLM. POST OpenAI-style chat-completions JSON with a real prompt in `messages`, "+
-			"attach a signed EIP-3009/Permit2 authorization as `X-PAYMENT`, and report what the agent does.",
+			"not a raw LLM. POST OpenAI-style chat-completions JSON: `messages` must include a user turn "+
+			"with your task (e.g. {\"role\":\"user\",\"content\":\"Summarise …\"}), plus a signed "+
+			"EIP-3009/Permit2 voucher as `X-PAYMENT`. Report what the agent returns.",
 		url, modelLine,
 	)
 
@@ -477,7 +492,10 @@ func httpCopy(url string, d PaymentDisplay) typeCopy {
 	if d.NetworkLabel != "" {
 		netClause = " Network: " + d.NetworkLabel + "."
 	}
-	prompt := fmt.Sprintf("Use the buy-x402 skill's `pay` command to call %s once.%s%s", url, priceClause, netClause)
+	prompt := fmt.Sprintf(
+		"Use the buy-x402 skill's `pay` command to call %s once.%s%s "+
+			"Use the method and payload the seller documents.",
+		url, priceClause, netClause)
 
 	priceWord := "the listed price"
 	if d.PriceDisplay != "" {

internal/x402/paymentrequired_test.go

@@ -208,6 +208,8 @@ func TestHTMLAware_InferenceShowsCLIPrimaryAndDescription(t *testing.T) {
 	// in "operator's hardware" appears raw, not entity-encoded.
 	mustContain(t, body, "agent runs locally")
 	mustContain(t, body, "remote operator's hardware")
+	mustContain(t, body, "OpenAI-style chat-completions")
+	mustContain(t, body, `/v1/chat/completions`)
 }
 
 // Agent offers should explain that the buyer is paying an autonomous
@@ -282,6 +284,7 @@ func TestHTMLAware_HTTPKeepsLegacyCopy(t *testing.T) {
 	body := w.Body.String()
 	mustContain(t, body, "Pay with your Obol Agent")
 	mustContain(t, body, "buy-x402 skill")
+	mustContain(t, body, "Use the method and payload the seller documents")
 	if strings.Contains(body, "obol buy inference") {
 		t.Errorf("http-type 402 page should NOT show the inference CLI primary card")
 	}

web/public-storefront/src/components/ServiceCard.tsx

@@ -179,7 +179,7 @@ function BuyViaObolAgent({ service }: { service: Service }) {
   }
 
   // http (default): legacy single-shot pay.
-  const prompt = `Use the buy-x402 skill's \`pay\` command to call ${service.endpoint} once. Pay ${service.price} on ${service.network}. Report what it returns.`;
+  const prompt = `Use the buy-x402 skill's \`pay\` command to call ${service.endpoint} once. Pay ${service.price} on ${service.network}. Use the method and payload the seller documents. Report what it returns.`;
   return (
     <div className="space-y-2">
       <p className="text-xs text-text-muted">