feat(phase6): bytes-based billing - dual metric support

- session_create_bytes() + session_add_bytes() for bytes-metric sessions
- session_is_expired() dispatches on config metric (bytes vs milliseconds)
- cashu_calculate_allotment() unified dispatcher for both metrics
- tollgate_api discovery/usage/session_event use configured metric
- config: metric field defaults to 'bytes', step_size_bytes=22020096 (21MB)
- 14 new unit tests (148 total passing)
- ASSERT_EQ_UINT64 macro added to test framework

1 files changed, 10 insertions, 0 deletions

diff --git a/main/config.c b/main/config.c
index 9257397..3e01efc 100644
--- a/main/config.c
+++ b/main/config.c
@@ -20,6 +20,8 @@ esp_err_t tollgate_config_init(void)
     g_config.ap_max_conn = 4;
     g_config.price_per_step = 21;
     g_config.step_size_ms = 60000;
+    g_config.step_size_bytes = 22020096;
+    strncpy(g_config.metric, "bytes", sizeof(g_config.metric) - 1);
     g_config.persist_threshold_sats = 1;
     g_config.nostr_publish_interval_s = 21600;
     g_config.client_enabled = false;
@@ -136,6 +138,14 @@ esp_err_t tollgate_config_init(void)
     cJSON *step = cJSON_GetObjectItem(root, "step_size_ms");
     if (step) g_config.step_size_ms = step->valueint;
 
+    cJSON *step_bytes = cJSON_GetObjectItem(root, "step_size_bytes");
+    if (step_bytes) g_config.step_size_bytes = step_bytes->valueint;
+
+    cJSON *metric = cJSON_GetObjectItem(root, "metric");
+    if (metric && cJSON_IsString(metric)) {
+        strncpy(g_config.metric, metric->valuestring, sizeof(g_config.metric) - 1);
+    }
+
     cJSON *persist = cJSON_GetObjectItem(root, "persist_threshold_sats");
     if (persist) g_config.persist_threshold_sats = (uint64_t)persist->valuedouble;