Phase 3: Nostr identity derivation + wifistr service discovery

- Add identity.c/h: HMAC-SHA512 derivation from nsec → npub, STA/AP MAC, SSID, AP IP
- Add nostr_event.c/h: NIP-01 event serialization + Schnorr signing (BIP-340)
- Add geohash.c/h: lat/lon to geohash encoding
- Add wifistr.c/h: kind 38787 event builder + WebSocket publish to Nostr relays
- Update config.c/h: nsec-based identity, Nostr relay/geo config, remove static SSID/IP
- Replace custom mbedTLS wallet with nucula library (libsecp256k1)
- Remove wallet.c/h, wallet_persist.c/h (replaced by nucula_lib component)
- Verified on Board A: derived SSID, captive portal, payment, wallet, wifistr publish

3 files changed, 247 insertions, 0 deletions

diff --git a/components/nucula_lib/CMakeLists.txt b/components/nucula_lib/CMakeLists.txt
new file mode 100644
index 0000000..ea1605e
--- /dev/null
+++ b/components/nucula_lib/CMakeLists.txt
@@ -0,0 +1,17 @@
+set(NUCULA_SRC ${CMAKE_CURRENT_SOURCE_DIR}/../../nucula_src/main)
+
+idf_component_register(
+    SRCS "nucula_wallet.cpp"
+         "${NUCULA_SRC}/crypto.c"
+         "${NUCULA_SRC}/wallet.cpp"
+         "${NUCULA_SRC}/cashu_json.cpp"
+         "${NUCULA_SRC}/nut10.cpp"
+         "${NUCULA_SRC}/hex.c"
+         "${NUCULA_SRC}/http.c"
+    INCLUDE_DIRS "."
+                 "${NUCULA_SRC}"
+    REQUIRES secp256k1
+    PRIV_REQUIRES log mbedtls nvs_flash esp_http_client json
+)
+
+target_compile_options(${COMPONENT_LIB} PRIVATE -Wno-unused-function)
diff --git a/components/nucula_lib/nucula_wallet.cpp b/components/nucula_lib/nucula_wallet.cpp
new file mode 100644
index 0000000..50583f9
--- /dev/null
+++ b/components/nucula_lib/nucula_wallet.cpp
@@ -0,0 +1,199 @@
+#include "nucula_wallet.h"
+#include "wallet.hpp"
+#include "cashu_json.hpp"
+#include "crypto.h"
+#include "hex.h"
+#include "esp_log.h"
+#include "secp256k1.h"
+#include "cJSON.h"
+#include <cstring>
+#include <string>
+#include <vector>
+
+static const char *TAG = "nucula_wallet";
+
+static secp256k1_context *s_ctx = nullptr;
+static cashu::Wallet *s_wallet = nullptr;
+
+static std::vector<cashu::Proof> &mutable_proofs()
+{
+    return const_cast<std::vector<cashu::Proof> &>(s_wallet->proofs());
+}
+
+esp_err_t nucula_wallet_init(const char *mint_url)
+{
+    if (s_wallet) return ESP_OK;
+
+    s_ctx = secp256k1_context_create(SECP256K1_CONTEXT_SIGN | SECP256K1_CONTEXT_VERIFY);
+    if (!s_ctx) {
+        ESP_LOGE(TAG, "Failed to create secp256k1 context");
+        return ESP_FAIL;
+    }
+
+    s_wallet = new cashu::Wallet(std::string(mint_url), s_ctx, 0);
+    if (!s_wallet) {
+        ESP_LOGE(TAG, "Failed to create wallet");
+        secp256k1_context_destroy(s_ctx);
+        s_ctx = nullptr;
+        return ESP_FAIL;
+    }
+
+    s_wallet->load_from_nvs();
+
+    if (!s_wallet->load_keysets()) {
+        ESP_LOGW(TAG, "Keyset load failed (may be offline)");
+    }
+
+    ESP_LOGI(TAG, "Wallet initialized: balance=%d proofs=%d keysets=%d",
+             s_wallet->balance(), (int)s_wallet->proofs().size(),
+             (int)s_wallet->keysets().size());
+    return ESP_OK;
+}
+
+esp_err_t nucula_wallet_receive(const char *token_str)
+{
+    if (!s_wallet || !token_str) return ESP_FAIL;
+
+    cashu::Token tok;
+    bool decoded = false;
+
+    if (strncmp(token_str, "cashuA", 6) == 0) {
+        decoded = cashu::deserialize_token_v3(token_str, tok);
+    }
+
+    if (!decoded) {
+        ESP_LOGE(TAG, "Failed to decode token");
+        return ESP_FAIL;
+    }
+
+    std::vector<cashu::Proof> proofs_out;
+    if (!s_wallet->receive(tok, proofs_out)) {
+        ESP_LOGE(TAG, "Receive failed");
+        return ESP_FAIL;
+    }
+
+    int total = 0;
+    for (const auto &p : proofs_out) total += p.amount;
+    ESP_LOGI(TAG, "Received %d sat (%d proofs), new balance=%d",
+             total, (int)proofs_out.size(), s_wallet->balance());
+    return ESP_OK;
+}
+
+esp_err_t nucula_wallet_send(uint64_t amount_sat, char *token_out, size_t token_out_size)
+{
+    if (!s_wallet) return ESP_FAIL;
+
+    int amount = (int)amount_sat;
+    std::vector<cashu::Proof> selected, remaining;
+    if (!s_wallet->select_proofs(amount, selected, remaining)) {
+        ESP_LOGE(TAG, "Insufficient balance for %d sat", amount);
+        return ESP_FAIL;
+    }
+
+    std::vector<cashu::Proof> new_proofs, change;
+    if (!s_wallet->swap(selected, (int)amount_sat, new_proofs, change)) {
+        ESP_LOGE(TAG, "Swap for send failed");
+        return ESP_FAIL;
+    }
+
+    cashu::Token token;
+    token.mint = s_wallet->mint_url();
+    token.unit = "sat";
+    for (auto &p : new_proofs) token.proofs.push_back(p);
+
+    std::string encoded = cashu::serialize_token_v3(token);
+    if (encoded.empty()) {
+        ESP_LOGE(TAG, "Token serialization failed");
+        return ESP_FAIL;
+    }
+
+    if (encoded.size() >= token_out_size) {
+        ESP_LOGE(TAG, "Token too large: %zu >= %zu", encoded.size(), token_out_size);
+        return ESP_FAIL;
+    }
+
+    memcpy(token_out, encoded.c_str(), encoded.size() + 1);
+
+    auto &proofs = mutable_proofs();
+    proofs = remaining;
+    for (auto &p : change) proofs.push_back(p);
+    s_wallet->save_proofs();
+
+    ESP_LOGI(TAG, "Sent %llu sat, token=%zu bytes, remaining balance=%d",
+             (unsigned long long)amount_sat, encoded.size(), s_wallet->balance());
+    return ESP_OK;
+}
+
+uint64_t nucula_wallet_balance(void)
+{
+    if (!s_wallet) return 0;
+    return (uint64_t)s_wallet->balance();
+}
+
+int nucula_wallet_proof_count(void)
+{
+    if (!s_wallet) return 0;
+    return (int)s_wallet->proofs().size();
+}
+
+char *nucula_wallet_proofs_json(void)
+{
+    if (!s_wallet) return nullptr;
+
+    const auto &proofs = s_wallet->proofs();
+    cJSON *arr = cJSON_CreateArray();
+    for (const auto &p : proofs) {
+        cJSON *obj = cJSON_CreateObject();
+        cJSON_AddNumberToObject(obj, "amount", p.amount);
+        cJSON_AddStringToObject(obj, "id", p.id.c_str());
+        cJSON_AddItemToArray(arr, obj);
+    }
+    char *json = cJSON_PrintUnformatted(arr);
+    cJSON_Delete(arr);
+    return json;
+}
+
+esp_err_t nucula_wallet_swap_all(void)
+{
+    if (!s_wallet) return ESP_FAIL;
+
+    auto &proofs = mutable_proofs();
+    if (proofs.empty()) {
+        ESP_LOGW(TAG, "No proofs to swap");
+        return ESP_FAIL;
+    }
+
+    int old_balance = s_wallet->balance();
+
+    std::vector<cashu::Proof> inputs = proofs;
+    std::vector<cashu::Proof> new_proofs, change;
+    if (!s_wallet->swap(inputs, -1, new_proofs, change)) {
+        ESP_LOGE(TAG, "Swap failed");
+        return ESP_FAIL;
+    }
+
+    proofs.clear();
+    for (auto &p : new_proofs) proofs.push_back(p);
+    for (auto &p : change) proofs.push_back(p);
+    s_wallet->save_proofs();
+
+    ESP_LOGI(TAG, "Swap complete: %d -> %d sat (%d proofs)",
+             old_balance, s_wallet->balance(), (int)proofs.size());
+    return ESP_OK;
+}
+
+void nucula_wallet_print_status(void)
+{
+    if (!s_wallet) {
+        ESP_LOGI(TAG, "Wallet not initialized");
+        return;
+    }
+    ESP_LOGI(TAG, "Wallet: balance=%d proofs=%d keysets=%d",
+             s_wallet->balance(), (int)s_wallet->proofs().size(),
+             (int)s_wallet->keysets().size());
+    const auto &proofs = s_wallet->proofs();
+    for (size_t i = 0; i < proofs.size(); i++) {
+        ESP_LOGI(TAG, "  [%d] amount=%d id=%s", (int)i,
+                 proofs[i].amount, proofs[i].id.c_str());
+    }
+}
diff --git a/components/nucula_lib/nucula_wallet.h b/components/nucula_lib/nucula_wallet.h
new file mode 100644
index 0000000..64b7c24
--- /dev/null
+++ b/components/nucula_lib/nucula_wallet.h
@@ -0,0 +1,31 @@
+#ifndef NUCULA_WALLET_H
+#define NUCULA_WALLET_H
+
+#include "esp_err.h"
+#include <stdint.h>
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+esp_err_t nucula_wallet_init(const char *mint_url);
+
+esp_err_t nucula_wallet_receive(const char *token_str);
+
+esp_err_t nucula_wallet_send(uint64_t amount_sat, char *token_out, size_t token_out_size);
+
+uint64_t nucula_wallet_balance(void);
+
+int nucula_wallet_proof_count(void);
+
+char *nucula_wallet_proofs_json(void);
+
+esp_err_t nucula_wallet_swap_all(void);
+
+void nucula_wallet_print_status(void);
+
+#ifdef __cplusplus
+}
+#endif
+
+#endif