fix(blufi): GET_WIFI_LIST triggers real-time scan with guaranteed response (#1964)

* fix(blufi): GET_WIFI_LIST triggers real-time scan with guaranteed response

Previously, ESP_BLUFI_EVENT_GET_WIFI_LIST waited for any in-progress scan
to finish and then returned the cached result. When the cache was empty
(e.g. after a config-mode transition that stopped the Wi-Fi driver),
_send_wifi_list() returned silently with no response frame, leaving the
App waiting until timeout.

Changes:
- GET_WIFI_LIST now clears the cache and starts a fresh scan immediately.
- _wifi_scan_event_handler calls _send_wifi_list() after every scan
  triggered by a GET_WIFI_LIST request.
- start_wifi_scan() calls esp_wifi_start() before esp_wifi_scan_start()
  to handle the case where the driver was stopped during a mode
  transition (ESP_ERR_WIFI_STATE is treated as already-started).
- _send_wifi_list() sends ESP_BLUFI_WIFI_SCAN_FAIL when no APs are
  found, so the App always receives a terminal response.
- Redundant static_cast in _wifi_scan_event_handler replaced with the
  existing local `self` pointer.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

* fix(blufi): preserve cache fast-path, fall back to live scan only when needed

Address review feedback on always-rescan latency regression.

The GET_WIFI_LIST handler now distinguishes three cases:

1. Scan in flight: defer the response via m_send_list_after_scan; the
   scan-done handler dispatches when it fires. Removes the previous
   blocking `while (m_scan_in_progress) vTaskDelay(500)` which would
   stall the BluFi event task indefinitely if the scan never completed.

2. Cache populated: respond from cache immediately (~50 ms, no latency
   change vs original behavior). _send_wifi_list() still kicks off an
   async refresh scan as before to keep the cache fresh.

3. Cache empty and no scan running: trigger a live scan and dispatch
   from the scan-done handler. If start_wifi_scan() fails, send
   ESP_BLUFI_WIFI_SCAN_FAIL so the App exits its wait state.

State variables are also disentangled:

- m_scan_should_save_ssid keeps its original meaning (write scan results
  into m_ap_records). Cleared during connect-to-AP so the connect-time
  scan does not pollute the cache.
- m_send_list_after_scan is new and tracks "the next scan-done event
  should respond to a pending GET_WIFI_LIST request". The previous PR
  conflated these two responsibilities onto m_scan_should_save_ssid,
  which would have caused init-time scans to spuriously emit a wifi list
  to the App.

start_wifi_scan() now returns bool so the caller can distinguish
"scan started or already running" from "could not start a scan".

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

---------

Co-authored-by: Yixin Shi <shiyixin@qiniu.com>
Co-authored-by: Claude Sonnet 4.6 <noreply@anthropic.com>

main/boards/common/blufi.h

@@ -25,8 +25,9 @@ public:
      * This method intelligently handles WiFi scanning based on current WiFi state:
      * - If WiFi config mode is active, it uses the existing scan results from WifiConfigurationAp
      * - Otherwise, it performs a dedicated scan without interfering with normal WiFi operations
+     * @return true if a scan was started (or was already in progress); false on failure.
      */
-    void start_wifi_scan();
+    bool start_wifi_scan();
 
     /**
      * @brief Initializes the Bluetooth controller, host, and Blufi profile.
@@ -143,5 +144,13 @@ private:
     // WiFi scan related
     std::vector<wifi_ap_record_t> m_ap_records;
     bool m_scan_in_progress = false;
+    // When true, scan results are stored in m_ap_records on scan completion.
+    // Cleared during connect-to-AP so that the connect-time scan does not
+    // overwrite the cache with results gathered for connection purposes.
     bool m_scan_should_save_ssid = true;
+    // When true, the next scan-done event responds to a pending GET_WIFI_LIST
+    // request from the App. Set by the GET_WIFI_LIST handler when no cache is
+    // available or a scan is already in flight; cleared by the scan-done
+    // handler after dispatching the response.
+    bool m_send_list_after_scan = false;
 };