Phase 4: TollGate client detection + auto-payment

- New tollgate_client.c/h: detect upstream TollGate (kind=10021),
  auto-pay via nucula wallet, session monitoring with 20% renewal
- State machine: IDLE→DETECTING→NEEDS_PAY→PAYING→PAID→RENEWING
- Blocking: upstream payment before local services start
- Synchronous wallet init (was async task)
- Client config: enabled, steps_to_buy, renewal_threshold_pct
- Updated PLAN.md with Phases 4-7 (client, payout, bytes, CVM)
- Updated CHECKLIST.md with all new phase items
- 30 new unit tests (all passing), 116 total

1 files changed, 46 insertions, 0 deletions

diff --git a/main/tollgate_client.h b/main/tollgate_client.h
new file mode 100644
index 0000000..2055e52
--- /dev/null
+++ b/main/tollgate_client.h
@@ -0,0 +1,46 @@
+#ifndef TOLLGATE_CLIENT_H
+#define TOLLGATE_CLIENT_H
+
+#include "esp_err.h"
+#include <stdint.h>
+#include <stdbool.h>
+
+#define TG_CLIENT_MAX_GW_IP_LEN       16
+#define TG_CLIENT_MAX_MINT_URL        256
+#define TG_CLIENT_MAX_METRIC          32
+
+typedef enum {
+    TG_CLIENT_IDLE,
+    TG_CLIENT_DETECTING,
+    TG_CLIENT_NO_TOLLGATE,
+    TG_CLIENT_NEEDS_PAY,
+    TG_CLIENT_PAYING,
+    TG_CLIENT_PAID,
+    TG_CLIENT_RENEWING,
+    TG_CLIENT_ERROR
+} tollgate_client_state_t;
+
+typedef struct {
+    bool is_tollgate;
+    int price_per_step;
+    int step_size_ms;
+    char mint_url[TG_CLIENT_MAX_MINT_URL];
+    char metric[TG_CLIENT_MAX_METRIC];
+} tollgate_discovery_t;
+
+esp_err_t tollgate_client_init(void);
+
+esp_err_t tollgate_client_on_sta_connected(const char *gw_ip_str);
+
+void tollgate_client_on_sta_disconnected(void);
+
+void tollgate_client_tick(void);
+
+tollgate_client_state_t tollgate_client_get_state(void);
+
+const tollgate_discovery_t *tollgate_client_get_discovery(void);
+
+int64_t tollgate_client_get_remaining_ms(void);
+int64_t tollgate_client_get_allotment_ms(void);
+
+#endif