Keep the image small enough for cubes on the old partition table

CLAUDE.md

@@ -152,6 +152,12 @@ scripts/capture_patterns.py --host cube.local <pattern id>` (frames come from
   watchdog's backtrace, printed mid-write, panicked the cube ("Cache disabled
   but cached memory region accessed", reset reason "interrupt watchdog"). Sleep
   a minimum each pass, as `Updates::animationLoop` and `Renderer::loop` do.
+- **The image must fit 0x1E0000 bytes.** Some cubes still have Arduino's old
+  `min_spiffs.csv` partition table (1,966,080-byte app slots), and a partition
+  table only changes over USB. A bigger image fails every update path at 99%
+  with `ESP_ERR_INVALID_SIZE`; v0.6.0 was 17 KB over. `scripts/size_guard.py`
+  fails the build first. Silent assertions buy ~59 KB; `-Os` would buy more
+  but slows rendering.
 - **Never flash `firmware.factory.bin` to a cube that is set up.** The merged
   image's padding covers NVS (0x9000-0xDFFF) and wipes WiFi, settings and the
   Spotify login. Update with the upload card or ArduinoOTA; over USB write only

platformio.ini

@@ -28,6 +28,7 @@ upload_port = cube.local
 ; copy in hub and lp-p2p.
 extra_scripts =
     scripts/idf_scripts.py
+    scripts/size_guard.py
 ; arduino-esp32's component manifest pulls in RainMaker, Insights, Zigbee,
 ; speech recognition, Modbus and more, whether or not the sketch uses them.
 ; The cube uses none of them. Removing them shortens the build and drops the

scripts/size_guard.py

@@ -0,0 +1,34 @@
+"""Fails the build when firmware.bin would not fit an older cube's app slot.
+
+Some cubes in the field still have the partition table from before
+min_spiffs_s3.csv: Arduino's min_spiffs.csv, whose app slots are 0x1E0000
+bytes. A partition table only changes over USB, so those cubes keep it through
+every OTA update, and an image larger than the slot fails at 99% with
+ESP_ERR_INVALID_SIZE -- the upload card, ArduinoOTA and the GitHub updater
+alike. v0.6.0 was 17 KB over and could not reach them.
+
+Keep this until no cube with the old table is left.
+"""
+
+Import("env")
+
+import os
+
+OLD_APP_SLOT = 0x1E0000  # app0/app1 in min_spiffs.csv
+
+
+def check_size(source, target, env):
+    path = target[0].get_abspath()
+    size = os.path.getsize(path)
+    margin = OLD_APP_SLOT - size
+    if margin < 0:
+        print(
+            "\n*** %s is %d bytes, %d over the %d-byte app slot that cubes with the "
+            "old min_spiffs.csv partition table have. They could not install it. "
+            "See scripts/size_guard.py.\n" % (os.path.basename(path), size, -margin, OLD_APP_SLOT)
+        )
+        env.Exit(1)
+    print("Old-layout app slot: %d bytes free (image %d of %d)" % (margin, size, OLD_APP_SLOT))
+
+
+env.AddPostAction("$BUILD_DIR/${PROGNAME}.bin", check_size)

sdkconfig.defaults

@@ -30,8 +30,12 @@ CONFIG_ARDUINO_RUN_NO_AFFINITY=y
 CONFIG_ARDUHAL_LOG_DEFAULT_LEVEL_INFO=y
 
 # Optimize for speed. The IDF default (-Og) is for debugging; the render loop's
-# per-pixel work runs measurably faster at -O2. Flash has plenty of room.
+# per-pixel work runs measurably faster at -O2.
 CONFIG_COMPILER_OPTIMIZATION_PERF=y
+# Assertions still stop the cube, but without compiling in each one's file
+# name and expression: about 59 KB, which keeps the image inside the 0x1E0000
+# app slots of cubes still on the old partition table (scripts/size_guard.py).
+CONFIG_COMPILER_OPTIMIZATION_ASSERTIONS_SILENT=y
 
 # CPU, RTOS, console
 CONFIG_ESP_DEFAULT_CPU_FREQ_MHZ_240=y