Phase 5: Lightning auto-payout with LNURL-pay and NUT-05 melt

- New lnurl_pay.c/h: LNURL-pay protocol (GET .well-known/lnurlp + callback)
- New lightning_payout.c/h: threshold-based auto-payout with multi-recipient split
- Extended nucula_wallet bridge with nucula_wallet_melt() (NUT-05)
- Config: payout section with multi-mint, multi-recipient, fee_tolerance
- Default: enabled, TollGate@coinos.io, min_payout=128, min_balance=64
- 18 new unit tests (all passing), 134 total

1 files changed, 156 insertions, 0 deletions

diff --git a/main/lnurl_pay.c b/main/lnurl_pay.c
new file mode 100644
index 0000000..bf3a932
--- /dev/null
+++ b/main/lnurl_pay.c
@@ -0,0 +1,156 @@
+#include "lnurl_pay.h"
+#include "esp_log.h"
+#include "esp_http_client.h"
+#include "esp_crt_bundle.h"
+#include "cJSON.h"
+#include <string.h>
+#include <stdlib.h>
+#include <stdio.h>
+
+static const char *TAG = "lnurl_pay";
+
+static esp_err_t http_get_json(const char *url, char *resp_buf, size_t resp_buf_size, int *status_out)
+{
+    esp_http_client_config_t config = {
+        .url = url,
+        .method = HTTP_METHOD_GET,
+        .timeout_ms = 15000,
+        .crt_bundle_attach = esp_crt_bundle_attach,
+    };
+    esp_http_client_handle_t client = esp_http_client_init(&config);
+    if (!client) return ESP_FAIL;
+
+    esp_err_t err = esp_http_client_open(client, 0);
+    if (err != ESP_OK) {
+        esp_http_client_cleanup(client);
+        return ESP_FAIL;
+    }
+
+    int content_length = esp_http_client_fetch_headers(client);
+    (void)content_length;
+    int status = esp_http_client_get_status_code(client);
+    if (status_out) *status_out = status;
+
+    int resp_len = esp_http_client_read(client, resp_buf, resp_buf_size - 1);
+    esp_http_client_cleanup(client);
+
+    if (resp_len < 0) return ESP_FAIL;
+    resp_buf[resp_len] = '\0';
+    return ESP_OK;
+}
+
+esp_err_t lnurl_get_invoice(const char *lightning_address, uint64_t amount_sats,
+                            char *bolt11_out, size_t bolt11_out_size)
+{
+    if (!lightning_address || !bolt11_out) return ESP_FAIL;
+
+    const char *at = strchr(lightning_address, '@');
+    if (!at) {
+        ESP_LOGE(TAG, "Invalid lightning address: missing '@'");
+        return ESP_FAIL;
+    }
+
+    size_t user_len = at - lightning_address;
+    char username[64];
+    if (user_len >= sizeof(username)) return ESP_FAIL;
+    memcpy(username, lightning_address, user_len);
+    username[user_len] = '\0';
+
+    const char *domain = at + 1;
+
+    char url[512];
+    snprintf(url, sizeof(url), "https://%s/.well-known/lnurlp/%s", domain, username);
+
+    ESP_LOGI(TAG, "LNURL-pay step 1: GET %s", url);
+
+    char *resp_buf = malloc(4096);
+    if (!resp_buf) return ESP_ERR_NO_MEM;
+
+    int status = 0;
+    esp_err_t err = http_get_json(url, resp_buf, 4096, &status);
+    if (err != ESP_OK || status != 200) {
+        ESP_LOGE(TAG, "LNURL-pay step 1 failed: status=%d err=%s", status, esp_err_to_name(err));
+        free(resp_buf);
+        return ESP_FAIL;
+    }
+
+    cJSON *root = cJSON_Parse(resp_buf);
+    if (!root) {
+        ESP_LOGE(TAG, "LNURL-pay step 1: invalid JSON");
+        free(resp_buf);
+        return ESP_FAIL;
+    }
+
+    cJSON *callback = cJSON_GetObjectItemCaseSensitive(root, "callback");
+    if (!callback || !cJSON_IsString(callback)) {
+        ESP_LOGE(TAG, "LNURL-pay step 1: missing callback");
+        cJSON_Delete(root);
+        free(resp_buf);
+        return ESP_FAIL;
+    }
+
+    char callback_url[512];
+    strncpy(callback_url, callback->valuestring, sizeof(callback_url) - 1);
+
+    cJSON *min_sendable = cJSON_GetObjectItemCaseSensitive(root, "minSendable");
+    cJSON *max_sendable = cJSON_GetObjectItemCaseSensitive(root, "maxSendable");
+
+    uint64_t amount_msat = amount_sats * 1000;
+    if (min_sendable && cJSON_IsNumber(min_sendable) && amount_msat < (uint64_t)min_sendable->valuedouble) {
+        ESP_LOGE(TAG, "Amount %llumsat below min %g", (unsigned long long)amount_msat, min_sendable->valuedouble);
+        cJSON_Delete(root);
+        free(resp_buf);
+        return ESP_FAIL;
+    }
+    if (max_sendable && cJSON_IsNumber(max_sendable) && amount_msat > (uint64_t)max_sendable->valuedouble) {
+        ESP_LOGE(TAG, "Amount %llumsat above max %g", (unsigned long long)amount_msat, max_sendable->valuedouble);
+        cJSON_Delete(root);
+        free(resp_buf);
+        return ESP_FAIL;
+    }
+
+    cJSON_Delete(root);
+
+    char callback_with_amount[768];
+    snprintf(callback_with_amount, sizeof(callback_with_amount), "%s%samount=%llu",
+             callback_url, strchr(callback_url, '?') ? "&" : "?",
+             (unsigned long long)amount_msat);
+
+    free(resp_buf);
+
+    ESP_LOGI(TAG, "LNURL-pay step 2: GET %s", callback_with_amount);
+
+    resp_buf = malloc(4096);
+    if (!resp_buf) return ESP_ERR_NO_MEM;
+
+    err = http_get_json(callback_with_amount, resp_buf, 4096, &status);
+    if (err != ESP_OK || status != 200) {
+        ESP_LOGE(TAG, "LNURL-pay step 2 failed: status=%d", status);
+        free(resp_buf);
+        return ESP_FAIL;
+    }
+
+    root = cJSON_Parse(resp_buf);
+    free(resp_buf);
+    if (!root) return ESP_FAIL;
+
+    cJSON *pr = cJSON_GetObjectItemCaseSensitive(root, "pr");
+    if (!pr || !cJSON_IsString(pr)) {
+        ESP_LOGE(TAG, "LNURL-pay step 2: missing 'pr' (bolt11)");
+        cJSON_Delete(root);
+        return ESP_FAIL;
+    }
+
+    size_t pr_len = strlen(pr->valuestring);
+    if (pr_len >= bolt11_out_size) {
+        ESP_LOGE(TAG, "BOLT11 too long: %zu >= %zu", pr_len, bolt11_out_size);
+        cJSON_Delete(root);
+        return ESP_FAIL;
+    }
+
+    memcpy(bolt11_out, pr->valuestring, pr_len + 1);
+    cJSON_Delete(root);
+
+    ESP_LOGI(TAG, "Got BOLT11 invoice (%zu bytes) for %llu sats", pr_len, (unsigned long long)amount_sats);
+    return ESP_OK;
+}