fix: keep wifi OTA off the heap floor (#2074)

OTA install streams the full 5.8MB image over a multi-minute TLS session
while wifi/LWIP already holds the big internal arena. Measured on
device, the arena bottomed out at ~7.7KB free with the largest
contiguous block down to ~2.4KB; for 80% of the download there wasn't
even a contiguous 8KB block. It finishes on a clean heap but tips into
OOM for anyone carrying more pre-OTA fragmentation.

Two avoidable drains, both in OtaUpdater:

- The esp_http_client RX/TX buffers were 8192/8192 on both the version
check and the install. RX only has to hold response headers (bodies
stream through the parser / OTA writer) and TX only carries our GET, so
trim both to 4096/1024. 4096 still fits the github->CDN redirect
headers; the 512 IDF default truncates them, which is why they got
oversized in the first place.

- installUpdate fired the progress callback every ~100ms perform
iteration, waking the render task on every tick. Its framebuffer work
fights the TLS session for the same arena, and epd can't really repaint
faster than a percent anyway. Throttle it to whole-percent changes.

On device, combined: floor 7.7KB -> 19KB, worstcase contiguous block
2.4KB -> 21KB, zero sub 8KB iterations across the whole download.

KOReaderSyncClient already uses small buffers; HttpDownloader is on the
Arduino HTTPClient stack with no equivalent knob, so neither changed.



Did you use AI tools to help write this code? partial, heap-exploration
assisted by Claude.

src/network/OtaUpdater.cpp

@@ -33,8 +33,11 @@ OtaUpdater::OtaUpdaterError OtaUpdater::checkForUpdate() {
   esp_http_client_config_t client_config = {
       .url = latestReleaseUrl,
       .event_handler = event_handler,
-      .buffer_size = 8192,
-      .buffer_size_tx = 8192,
+      // 4096 holds the API response headers; the 32KB body streams through the
+      // parser in chunks so RX needn't be larger. TX only carries our GET.
+      // Both free before installUpdate, so smaller leaves it less fragmentation.
+      .buffer_size = 4096,
+      .buffer_size_tx = 1024,
       .user_data = &releaseParser,
       .skip_cert_common_name_check = true,
       .crt_bundle_attach = esp_crt_bundle_attach,
@@ -151,12 +154,11 @@ OtaUpdater::OtaUpdaterError OtaUpdater::installUpdate(ProgressCallback onProgres
   esp_http_client_config_t client_config = {
       .url = otaUrl.c_str(),
       .timeout_ms = 15000,
-      /* Default HTTP client buffer size 512 byte only
-       * not sufficient to handle URL redirection cases or
-       * parsing of large HTTP headers.
-       */
-      .buffer_size = 8192,
-      .buffer_size_tx = 8192,
+      // 4096 holds the github->CDN redirect headers (the 512 default truncates
+      // them); TX only carries our GET. Both are contiguous blocks contending
+      // with the TLS handshake on a tight internal arena, so keep them minimal.
+      .buffer_size = 4096,
+      .buffer_size_tx = 1024,
       .skip_cert_common_name_check = true,
       .crt_bundle_attach = esp_crt_bundle_attach,
       .keep_alive_enable = true,
@@ -176,10 +178,21 @@ OtaUpdater::OtaUpdaterError OtaUpdater::installUpdate(ProgressCallback onProgres
     return INTERNAL_UPDATE_ERROR;
   }
 
+  int lastReportedPct = -1;
   do {
     esp_err = esp_https_ota_perform(ota_handle);
     processedSize = esp_https_ota_get_image_len_read(ota_handle);
-    if (onProgress) onProgress(ctx);
+    // Fire the callback only on whole-percent change. Without this it fired
+    // every ~100ms perform iteration, waking the render task whose framebuffer
+    // work contends with TLS on the same internal arena. E-ink can't repaint
+    // faster than a percent tick anyway.
+    if (onProgress && totalSize > 0) {
+      const int pct = static_cast<int>(static_cast<uint64_t>(processedSize) * 100 / totalSize);
+      if (pct != lastReportedPct) {
+        lastReportedPct = pct;
+        onProgress(ctx);
+      }
+    }
     delay(100);  // TODO: should we replace this with something better?
   } while (esp_err == ESP_ERR_HTTPS_OTA_IN_PROGRESS);