From 4dc5c89e25ebfa823262f792fa7ed1c48b61d25d Mon Sep 17 00:00:00 2001
From: "torlando-agent[bot]"
 <281092095+torlando-agent[bot]@users.noreply.github.com>
Date: Fri, 19 Jun 2026 10:53:33 -0400
Subject: [PATCH] fix: scope LVGL lock to the snapshot in T:SCREENSHOT (not the
 serial dump)

LVGL_LOCK() was held for the entire base64 serial dump (~18s for a 320x240
frame), blocking the LVGL render task the whole time and tripping the 5s
LVGLLock recursive-take timeout assert in debug builds (crash on every
screenshot). lv_snapshot_take() copies the pixels into its own buffer, so the
lock is only needed for the snapshot itself -- scope it there, dump the copy
unlocked, and re-take the lock only to free the snapshot.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01UWZuYkHBRqNb6BZHV8sTG5
---
 src/main.cpp | 24 ++++++++++++++++--------
 1 file changed, 16 insertions(+), 8 deletions(-)

diff --git a/src/main.cpp b/src/main.cpp
index b1f46c03..8f5b0e80 100644
--- a/src/main.cpp
+++ b/src/main.cpp
@@ -2086,15 +2086,23 @@ static void handle_test_hook_command(const String& line) {
         // all lines between the markers, base64-decodes, and converts
         // to PNG. FMT carries the byte order (`be` when LV_COLOR_16_SWAP
         // is on, `le` otherwise) so the decoder doesn't have to guess.
-        LVGL_LOCK();
-        lv_obj_t* scr = lv_scr_act();
-        if (!scr) {
-            Serial.println("T:ERR no active screen");
-            return;
+        // Hold the LVGL lock ONLY for the snapshot: lv_snapshot_take() copies
+        // the screen pixels into a freshly-allocated buffer, so live LVGL state
+        // isn't touched during the ~18s base64 serial dump below. Holding the
+        // recursive mutex across the whole dump blocks the LVGL render task and
+        // trips the 5s LVGLLock timeout assert (LVGLLock.h) in debug builds.
+        lv_img_dsc_t* snap = nullptr;
+        {
+            LVGL_LOCK();
+            lv_obj_t* scr = lv_scr_act();
+            if (!scr) {
+                Serial.println("T:ERR no active screen");
+                return;
+            }
+            snap = lv_snapshot_take(scr, LV_IMG_CF_TRUE_COLOR);
         }
-        lv_img_dsc_t* snap = lv_snapshot_take(scr, LV_IMG_CF_TRUE_COLOR);
         if (!snap || !snap->data) {
-            if (snap) lv_snapshot_free(snap);
+            if (snap) { LVGL_LOCK(); lv_snapshot_free(snap); }
             Serial.println("T:ERR snapshot failed (PSRAM exhausted?)");
             return;
         }
@@ -2150,7 +2158,7 @@ static void handle_test_hook_command(const String& line) {
             Serial.println(line);
         }
         Serial.println("T:SCREENSHOT END");
-        lv_snapshot_free(snap);
+        { LVGL_LOCK(); lv_snapshot_free(snap); }
     }
     else if (cmd == "T:CALL_INJECT") {
         // T:CALL_INJECT <on|off> [freq_hz] [amp_pct]