Testing infrastructure: AGENTS.md rules + unit test framework + geohash tests (11/11 pass)

- Add AGENTS.md: full project context + mandatory testing rules for AI sessions
- Add tests/unit/ with host-compiled C unit test infrastructure
- Clean stubs approach: ESP-IDF type stubs in tests/unit/stubs/, no source modifications
- Fix geohash.c bit extraction bug (3-byte span) found by unit tests
- test_geohash: 11/11 passing with reference vectors (Munich, NYC, origin, boundaries)

23 files changed, 295 insertions, 0 deletions

diff --git a/tests/unit/stubs/dhcpserver/dhcpserver.h b/tests/unit/stubs/dhcpserver/dhcpserver.h
new file mode 100644
index 0000000..659f2c3
--- /dev/null
+++ b/tests/unit/stubs/dhcpserver/dhcpserver.h
@@ -0,0 +1,4 @@
+#ifndef STUBS_DHCPSERVER_DHCP_H
+#define STUBS_DHCPSERVER_DHCP_H
+
+#endif
diff --git a/tests/unit/stubs/esp_crt_bundle.h b/tests/unit/stubs/esp_crt_bundle.h
new file mode 100644
index 0000000..dfb9bb1
--- /dev/null
+++ b/tests/unit/stubs/esp_crt_bundle.h
@@ -0,0 +1,6 @@
+#ifndef STUBS_ESP_CRT_BUNDLE_H
+#define STUBS_ESP_CRT_BUNDLE_H
+
+static inline void *esp_crt_bundle_attach(void *conf) { (void)conf; return NULL; }
+
+#endif
diff --git a/tests/unit/stubs/esp_err.h b/tests/unit/stubs/esp_err.h
new file mode 100644
index 0000000..84c3734
--- /dev/null
+++ b/tests/unit/stubs/esp_err.h
@@ -0,0 +1,18 @@
+#ifndef STUBS_ESP_ERR_H
+#define STUBS_ESP_ERR_H
+
+#include <stdint.h>
+#include <stdio.h>
+#include <stdlib.h>
+
+typedef int esp_err_t;
+
+#define ESP_OK          0
+#define ESP_FAIL        -1
+#define ESP_ERR_INVALID_ARG  0x102
+#define ESP_ERR_NO_MEM       0x101
+#define ESP_ERR_NOT_FOUND    0x104
+
+#define ESP_ERROR_CHECK(x) do { if ((x) != 0) { fprintf(stderr, "ESP_ERROR_CHECK failed: 0x%x\n", (int)(x)); abort(); } } while(0)
+
+#endif
diff --git a/tests/unit/stubs/esp_event.h b/tests/unit/stubs/esp_event.h
new file mode 100644
index 0000000..baea064
--- /dev/null
+++ b/tests/unit/stubs/esp_event.h
@@ -0,0 +1,8 @@
+#ifndef STUBS_ESP_EVENT_H
+#define STUBS_ESP_EVENT_H
+
+#include "esp_err.h"
+
+static inline esp_err_t esp_event_loop_create_default(void) { return ESP_OK; }
+
+#endif
diff --git a/tests/unit/stubs/esp_http_client.h b/tests/unit/stubs/esp_http_client.h
new file mode 100644
index 0000000..4169714
--- /dev/null
+++ b/tests/unit/stubs/esp_http_client.h
@@ -0,0 +1,12 @@
+#ifndef STUBS_ESP_HTTP_CLIENT_H
+#define STUBS_ESP_HTTP_CLIENT_H
+
+#include "esp_err.h"
+
+typedef void *esp_http_client_handle_t;
+
+typedef struct {
+    int cert_pem;
+} esp_http_client_config_t;
+
+#endif
diff --git a/tests/unit/stubs/esp_http_server.h b/tests/unit/stubs/esp_http_server.h
new file mode 100644
index 0000000..22a5624
--- /dev/null
+++ b/tests/unit/stubs/esp_http_server.h
@@ -0,0 +1,10 @@
+#ifndef STUBS_ESP_HTTP_SERVER_H
+#define STUBS_ESP_HTTP_SERVER_H
+
+#include "esp_err.h"
+#include <stdint.h>
+
+typedef void *httpd_handle_t;
+typedef struct httpd_req httpd_req_t;
+
+#endif
diff --git a/tests/unit/stubs/esp_log.h b/tests/unit/stubs/esp_log.h
new file mode 100644
index 0000000..f353fe9
--- /dev/null
+++ b/tests/unit/stubs/esp_log.h
@@ -0,0 +1,10 @@
+#ifndef STUBS_ESP_LOG_H
+#define STUBS_ESP_LOG_H
+
+#include <stdio.h>
+
+#define ESP_LOGI(tag, fmt, ...) do { printf("I %s: " fmt "\n", tag, ##__VA_ARGS__); } while(0)
+#define ESP_LOGW(tag, fmt, ...) do { printf("W %s: " fmt "\n", tag, ##__VA_ARGS__); } while(0)
+#define ESP_LOGE(tag, fmt, ...) do { fprintf(stderr, "E %s: " fmt "\n", tag, ##__VA_ARGS__); } while(0)
+
+#endif
diff --git a/tests/unit/stubs/esp_mac.h b/tests/unit/stubs/esp_mac.h
new file mode 100644
index 0000000..ddc80d4
--- /dev/null
+++ b/tests/unit/stubs/esp_mac.h
@@ -0,0 +1,19 @@
+#ifndef STUBS_ESP_MAC_H
+#define STUBS_ESP_MAC_H
+
+#include <stdint.h>
+#include <string.h>
+
+static inline int esp_read_mac(uint8_t *mac, int type) {
+    (void)type;
+    memset(mac, 0, 6);
+    mac[0] = 0x02;
+    mac[1] = 0x00;
+    mac[2] = 0x00;
+    mac[3] = 0x00;
+    mac[4] = 0xBE;
+    mac[5] = 0xEF;
+    return 0;
+}
+
+#endif
diff --git a/tests/unit/stubs/esp_netif.h b/tests/unit/stubs/esp_netif.h
new file mode 100644
index 0000000..f009537
--- /dev/null
+++ b/tests/unit/stubs/esp_netif.h
@@ -0,0 +1,17 @@
+#ifndef STUBS_ESP_NETIF_H
+#define STUBS_ESP_NETIF_H
+
+#include <stdint.h>
+
+typedef struct {
+    uint32_t addr;
+} esp_ip4_addr_t;
+
+#define IPSTR "%d.%d.%d.%d"
+#define IP2STR(ip) ((ip)->addr & 0xff), (((ip)->addr >> 8) & 0xff), (((ip)->addr >> 16) & 0xff), (((ip)->addr >> 24) & 0xff)
+
+static inline void IP4_ADDR(esp_ip4_addr_t *ip, uint8_t a, uint8_t b, uint8_t c, uint8_t d) {
+    ip->addr = ((uint32_t)a) | ((uint32_t)b << 8) | ((uint32_t)c << 16) | ((uint32_t)d << 24);
+}
+
+#endif
diff --git a/tests/unit/stubs/esp_spiffs.h b/tests/unit/stubs/esp_spiffs.h
new file mode 100644
index 0000000..ae6a127
--- /dev/null
+++ b/tests/unit/stubs/esp_spiffs.h
@@ -0,0 +1,15 @@
+#ifndef STUBS_ESP_SPIFFS_H
+#define STUBS_ESP_SPIFFS_H
+
+#include "esp_err.h"
+
+typedef struct {
+    const char *base_path;
+    const char *partition_label;
+    int max_files;
+    bool format_if_mount_failed;
+} esp_vfs_spiffs_conf_t;
+
+static inline esp_err_t esp_vfs_spiffs_register(const esp_vfs_spiffs_conf_t *conf) { (void)conf; return ESP_OK; }
+
+#endif
diff --git a/tests/unit/stubs/esp_system.h b/tests/unit/stubs/esp_system.h
new file mode 100644
index 0000000..8e63c80
--- /dev/null
+++ b/tests/unit/stubs/esp_system.h
@@ -0,0 +1,4 @@
+#ifndef STUBS_ESP_SYSTEM_H
+#define STUBS_ESP_SYSTEM_H
+
+#endif
diff --git a/tests/unit/stubs/esp_tls.h b/tests/unit/stubs/esp_tls.h
new file mode 100644
index 0000000..7ded63a
--- /dev/null
+++ b/tests/unit/stubs/esp_tls.h
@@ -0,0 +1,25 @@
+#ifndef STUBS_ESP_TLS_H
+#define STUBS_ESP_TLS_H
+
+#include "esp_err.h"
+
+typedef struct esp_tls esp_tls_t;
+
+typedef struct {
+    void *crt_bundle_attach;
+    int use_global_ca_store;
+} esp_tls_cfg_t;
+
+static inline esp_tls_t *esp_tls_init(void) { return (esp_tls_t*)1; }
+static inline int esp_tls_conn_new_sync(const char *h, int hl, int port, const esp_tls_cfg_t *cfg, esp_tls_t *tls) {
+    (void)h; (void)hl; (void)port; (void)cfg; (void)tls; return -1;
+}
+static inline int esp_tls_conn_write(esp_tls_t *tls, const void *data, size_t len) {
+    (void)tls; (void)data; (void)len; return len;
+}
+static inline int esp_tls_conn_read(esp_tls_t *tls, void *data, size_t len) {
+    (void)tls; (void)data; (void)len; return 0;
+}
+static inline void esp_tls_conn_destroy(esp_tls_t *tls) { (void)tls; }
+
+#endif
diff --git a/tests/unit/stubs/esp_wifi.h b/tests/unit/stubs/esp_wifi.h
new file mode 100644
index 0000000..6aa5787
--- /dev/null
+++ b/tests/unit/stubs/esp_wifi.h
@@ -0,0 +1,40 @@
+#ifndef STUBS_ESP_WIFI_H
+#define STUBS_ESP_WIFI_H
+
+#include <stdint.h>
+#include <string.h>
+#include "esp_err.h"
+
+#define WIFI_IF_STA 0
+#define WIFI_IF_AP  1
+
+#define WIFI_AUTH_WPA2_PSK 3
+#define WIFI_AUTH_OPEN     0
+
+#define WIFI_MODE_APSTA 3
+
+typedef struct {
+    struct {
+        uint8_t ssid[32];
+        uint8_t password[64];
+        uint8_t channel;
+        uint8_t max_connection;
+        uint8_t ssid_hidden;
+        int authmode;
+    } ap;
+    struct {
+        uint8_t ssid[32];
+        uint8_t password[64];
+        int threshold;
+        struct {
+            int authmode;
+        } sta;
+    } sta;
+} wifi_config_t;
+
+static inline esp_err_t esp_wifi_set_mac(int ifx, const uint8_t *mac) { (void)ifx; (void)mac; return ESP_OK; }
+static inline esp_err_t esp_wifi_set_config(int ifx, const wifi_config_t *cfg) { (void)ifx; (void)cfg; return ESP_OK; }
+static inline esp_err_t esp_wifi_set_mode(uint8_t mode) { (void)mode; return ESP_OK; }
+static inline esp_err_t esp_wifi_start(void) { return ESP_OK; }
+
+#endif
diff --git a/tests/unit/stubs/freertos/FreeRTOS.h b/tests/unit/stubs/freertos/FreeRTOS.h
new file mode 100644
index 0000000..0fee758
--- /dev/null
+++ b/tests/unit/stubs/freertos/FreeRTOS.h
@@ -0,0 +1,11 @@
+#ifndef STUBS_FREERTOS_FREERTOS_H
+#define STUBS_FREERTOS_FREERTOS_H
+
+#include <stdint.h>
+
+static inline uint32_t xTaskGetTickCount(void) { return 0; }
+static inline void vTaskDelay(uint32_t ticks) { (void)ticks; }
+#define pdMS_TO_TICKS(ms) ((ms) / 10)
+#define portMAX_DELAY 0xFFFFFFFF
+
+#endif
diff --git a/tests/unit/stubs/freertos/event_groups.h b/tests/unit/stubs/freertos/event_groups.h
new file mode 100644
index 0000000..28f6403
--- /dev/null
+++ b/tests/unit/stubs/freertos/event_groups.h
@@ -0,0 +1,13 @@
+#ifndef STUBS_FREERTOS_EVENT_GROUPS_H
+#define STUBS_FREERTOS_EVENT_GROUPS_H
+
+#include <stdint.h>
+
+typedef void *EventGroupHandle_t;
+#define BIT0 (1 << 0)
+
+static inline EventGroupHandle_t xEventGroupCreate(void) { return (EventGroupHandle_t)1; }
+static inline uint32_t xEventGroupSetBits(EventGroupHandle_t eg, uint32_t bits) { (void)eg; return bits; }
+static inline uint32_t xEventGroupClearBits(EventGroupHandle_t eg, uint32_t bits) { (void)eg; return bits; }
+
+#endif
diff --git a/tests/unit/stubs/freertos/task.h b/tests/unit/stubs/freertos/task.h
new file mode 100644
index 0000000..3855d41
--- /dev/null
+++ b/tests/unit/stubs/freertos/task.h
@@ -0,0 +1,19 @@
+#ifndef STUBS_FREERTOS_TASK_H
+#define STUBS_FREERTOS_TASK_H
+
+#include <stdint.h>
+#include <stdlib.h>
+
+typedef void *TaskHandle_t;
+typedef void *SemaphoreHandle_t;
+
+static inline void vTaskDelete(TaskHandle_t t) { (void)t; }
+static inline SemaphoreHandle_t xSemaphoreCreateMutex(void) { return (SemaphoreHandle_t)malloc(1); }
+static inline void vSemaphoreDelete(SemaphoreHandle_t s) { free(s); }
+static inline int xSemaphoreTake(SemaphoreHandle_t s, uint32_t blk) { (void)s; (void)blk; return 1; }
+static inline int xSemaphoreGive(SemaphoreHandle_t s) { (void)s; return 1; }
+static inline int xTaskCreate(void (*fn)(void*), const char *n, uint32_t st, void *p, uint32_t pri, TaskHandle_t *h) {
+    (void)fn; (void)n; (void)st; (void)p; (void)pri; (void)h; return 1;
+}
+
+#endif
diff --git a/tests/unit/stubs/freertos/timers.h b/tests/unit/stubs/freertos/timers.h
new file mode 100644
index 0000000..7575807
--- /dev/null
+++ b/tests/unit/stubs/freertos/timers.h
@@ -0,0 +1,15 @@
+#ifndef STUBS_FREERTOS_TIMERS_H
+#define STUBS_FREERTOS_TIMERS_H
+
+#include <stdint.h>
+
+typedef void *TimerHandle_t;
+
+static inline TimerHandle_t xTimerCreate(const char *n, uint32_t pd, int ux, void *id, void *cb) {
+    (void)n; (void)pd; (void)ux; (void)id; (void)cb; return (TimerHandle_t)1;
+}
+static inline int xTimerStart(TimerHandle_t t, uint32_t blk) { (void)t; (void)blk; return 1; }
+static inline int xTimerStop(TimerHandle_t t, uint32_t blk) { (void)t; (void)blk; return 1; }
+static inline void xTimerDelete(TimerHandle_t t, uint32_t blk) { (void)t; (void)blk; }
+
+#endif
diff --git a/tests/unit/stubs/lwip/ip4_addr.h b/tests/unit/stubs/lwip/ip4_addr.h
new file mode 100644
index 0000000..174211b
--- /dev/null
+++ b/tests/unit/stubs/lwip/ip4_addr.h
@@ -0,0 +1,19 @@
+#ifndef STUBS_LWIP_IP4_ADDR_H
+#define STUBS_LWIP_IP4_ADDR_H
+
+#include <stdint.h>
+
+typedef struct {
+    uint32_t addr;
+} ip4_addr_t;
+
+typedef ip4_addr_t esp_ip4_addr_t;
+
+#define IPSTR "%d.%d.%d.%d"
+#define IP2STR(ip) ((ip)->addr & 0xff), (((ip)->addr >> 8) & 0xff), (((ip)->addr >> 16) & 0xff), (((ip)->addr >> 24) & 0xff)
+
+static inline void IP4_ADDR(esp_ip4_addr_t *ip, uint8_t a, uint8_t b, uint8_t c, uint8_t d) {
+    ip->addr = ((uint32_t)a) | ((uint32_t)b << 8) | ((uint32_t)c << 16) | ((uint32_t)d << 24);
+}
+
+#endif
diff --git a/tests/unit/stubs/lwip/napt.h b/tests/unit/stubs/lwip/napt.h
new file mode 100644
index 0000000..c6a5ca1
--- /dev/null
+++ b/tests/unit/stubs/lwip/napt.h
@@ -0,0 +1,6 @@
+#ifndef STUBS_LWIP_NAPT_H
+#define STUBS_LWIP_NAPT_H
+
+static inline void ip_napt_enable(uint32_t num, int enable) { (void)num; (void)enable; }
+
+#endif
diff --git a/tests/unit/stubs/lwip/netdb.h b/tests/unit/stubs/lwip/netdb.h
new file mode 100644
index 0000000..b71bab8
--- /dev/null
+++ b/tests/unit/stubs/lwip/netdb.h
@@ -0,0 +1,4 @@
+#ifndef STUBS_LWIP_NETDB_H
+#define STUBS_LWIP_NETDB_H
+
+#endif
diff --git a/tests/unit/stubs/lwip/netif.h b/tests/unit/stubs/lwip/netif.h
new file mode 100644
index 0000000..461a64e
--- /dev/null
+++ b/tests/unit/stubs/lwip/netif.h
@@ -0,0 +1,4 @@
+#ifndef STUBS_LWIP_NETIF_H
+#define STUBS_LWIP_NETIF_H
+
+#endif
diff --git a/tests/unit/stubs/lwip/sockets.h b/tests/unit/stubs/lwip/sockets.h
new file mode 100644
index 0000000..44f03ac
--- /dev/null
+++ b/tests/unit/stubs/lwip/sockets.h
@@ -0,0 +1,4 @@
+#ifndef STUBS_LWIP_SOCKETS_H
+#define STUBS_LWIP_SOCKETS_H
+
+#endif
diff --git a/tests/unit/stubs/nvs_flash.h b/tests/unit/stubs/nvs_flash.h
new file mode 100644
index 0000000..4424a9a
--- /dev/null
+++ b/tests/unit/stubs/nvs_flash.h
@@ -0,0 +1,12 @@
+#ifndef STUBS_NVS_FLASH_H
+#define STUBS_NVS_FLASH_H
+
+#include "esp_err.h"
+
+#define ESP_ERR_NVS_NO_FREE_PAGES    0x1101
+#define ESP_ERR_NVS_NEW_VERSION_FOUND 0x1102
+
+static inline esp_err_t nvs_flash_init(void) { return ESP_OK; }
+static inline esp_err_t nvs_flash_erase(void) { return ESP_OK; }
+
+#endif