feat(screenshot): extend e-ink screenshot support via GxEPD2 patch

- Add lib/GxEPD2-patch/src/GxEPD2_BW.h: local patched copy of GxEPD2_BW.h
  that exposes getBuffer()/getBufferSize() under ENABLE_SCREENSHOT guard.
  Include guard (_GxEPD2_BW_H_) prevents double-inclusion of the installed
  library version.

- GxEPDDisplay.h: use patched header via relative include when
  ENABLE_SCREENSHOT so the patch takes precedence over the installed lib
  (PlatformIO adds library paths before -I build_flags).

- DisplayDriver.h: add virtual getBuffer()/getBufferSize()/getDisplayType()
  defaults (nullptr/0/0) under ENABLE_SCREENSHOT.

- SH1106Display.h / SSD1306Display.h / GxEPDDisplay.h: add concrete overrides;
  getDisplayType() returns 0 (OLED) or 1 (e-ink).

- MyMesh.cpp/h: replace fragile C-cast with virtual dispatch in
  handleScreenshotRequest(); extend 5-byte header to 6 bytes by appending
  display_type so the host tool can decode the correct pixel layout.

- tools/screenshot.py: parse 6-byte header; add eink_buffer_to_image()
  that decodes the row-major MSB-first GxEPD2 buffer with DISPLAY_ROTATION=1
  (phys_x = 127-ly, phys_y = lx); dispatch on display_type.

- variants/wio-tracker-l1-eink/platformio.ini: add
  [env:WioTrackerL1Eink_companion_dual_dev] with ENABLE_SCREENSHOT.
- variants/wio-tracker-l1/platformio.ini: unchanged (OLED env already exists).

Builds verified: WioTrackerL1Eink_companion_dual_dev SUCCESS,
                 WioTrackerL1Eink_companion_radio_ble SUCCESS (unaffected).

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

examples/companion_radio/MyMesh.cpp

@@ -2077,35 +2077,19 @@ void MyMesh::handleScreenshotRequest() {
         writeErrFrame(ERR_CODE_UNSUPPORTED_CMD);
         return;
     }
-    
+
     DisplayDriver* display = ui_task->getDisplay();
     if (!display) {
         writeErrFrame(ERR_CODE_UNSUPPORTED_CMD);
         return;
     }
-    
-    uint8_t* buffer = nullptr;
-    int bufferSize = 0;
-    
-    // Try SH1106Display first (used by Wio L1)
-    // Use C-style cast since RTTI is disabled (-fno-rtti)
-    SH1106Display* sh1106 = (SH1106Display*)display;
-    if (sh1106) {
-        buffer = sh1106->getBuffer();
-        bufferSize = (display->width() * display->height()) / 8;
-    } else {
-        // Fallback: try SSD1306Display
-        SSD1306Display* ssd1306 = (SSD1306Display*)display;
-        if (ssd1306) {
-            buffer = ssd1306->getBuffer();
-            bufferSize = (display->width() * display->height()) / 8;
-        }
-    }
-    
+
+    const uint8_t* buffer = display->getBuffer();
+    uint16_t bufferSize = display->getBufferSize();
+
     if (buffer && bufferSize > 0) {
         sendScreenshotResponse(display, buffer, bufferSize);
     } else {
-        // No supported display type
         writeErrFrame(ERR_CODE_UNSUPPORTED_CMD);
     }
     #else
@@ -2113,26 +2097,26 @@ void MyMesh::handleScreenshotRequest() {
     #endif
 }
 
-void MyMesh::sendScreenshotResponse(DisplayDriver* display, uint8_t* buffer, int bufferSize) {
-    // MAX_FRAME_SIZE is 172 bytes, but we need to send 1026 bytes (3 header + 1024 buffer)
-    // We need to split into multiple frames
-    // Frame format: RESP_CODE_SCREENSHOT, width, height, chunk_index, total_chunks, [chunk_data...]
-    
-    const int MAX_DATA_PER_FRAME = MAX_FRAME_SIZE - 5; // 5 bytes header
+void MyMesh::sendScreenshotResponse(DisplayDriver* display, const uint8_t* buffer, uint16_t bufferSize) {
+    // Frame format: RESP_CODE_SCREENSHOT, width, height, chunk_idx, total_chunks, display_type, [data]
+    // display_type: 0=OLED (page-based), 1=e-ink (row-major, MSB-first, 1=white/0=black)
+    const int HEADER_SIZE = 6;
+    const int MAX_DATA_PER_FRAME = MAX_FRAME_SIZE - HEADER_SIZE;
     int totalChunks = (bufferSize + MAX_DATA_PER_FRAME - 1) / MAX_DATA_PER_FRAME;
-    
+
     for (int chunkIdx = 0; chunkIdx < totalChunks; chunkIdx++) {
         int i = 0;
         out_frame[i++] = RESP_CODE_SCREENSHOT;
-        out_frame[i++] = display->width();
-        out_frame[i++] = display->height();
-        out_frame[i++] = chunkIdx;
-        out_frame[i++] = totalChunks;
-        
-        int chunkSize = min(MAX_DATA_PER_FRAME, bufferSize - chunkIdx * MAX_DATA_PER_FRAME);
+        out_frame[i++] = (uint8_t)display->width();
+        out_frame[i++] = (uint8_t)display->height();
+        out_frame[i++] = (uint8_t)chunkIdx;
+        out_frame[i++] = (uint8_t)totalChunks;
+        out_frame[i++] = display->getDisplayType();
+
+        int chunkSize = min(MAX_DATA_PER_FRAME, (int)bufferSize - chunkIdx * MAX_DATA_PER_FRAME);
         memcpy(&out_frame[i], buffer + chunkIdx * MAX_DATA_PER_FRAME, chunkSize);
         i += chunkSize;
-        
+
         _serial->writeFrame(out_frame, i);
     }
 }

examples/companion_radio/MyMesh.h

@@ -229,7 +229,7 @@ private:
   bool isValidClientRepeatFreq(uint32_t f) const;
 #ifdef ENABLE_SCREENSHOT
   void handleScreenshotRequest();
-  void sendScreenshotResponse(DisplayDriver* display, uint8_t* buffer, int bufferSize);
+  void sendScreenshotResponse(DisplayDriver* display, const uint8_t* buffer, uint16_t bufferSize);
 #endif
 
   UITask* getUITask() { return (UITask*)_ui; }