chore: migrate from open-x4-sdk to freeink-sdk (#2449)

This PR moves us from the xteink openx4 SDK to the freeink sdk from
https://freeink.org. Out of the box there are NO changes needed in the
firmware to support this swap, it all magically works as is. However as
we support more than just the x3/x4 devices, this sdk allows us to pass
env vars into the build commands to include support for other devices.
As support for new hardware such as touch screens and bluetooth are
added the xteink builds decide at compile time if the libraries are used
or not. For example right now the freeinkui and icons libraries are in
the platform.io file but as they are not used anywhere, they won't be
included in the final build. Once the touch branch and sd themes branch
are merged in this sdk is required for them to function correctly. All
the docs for freeink are available at freeink.org/docs. x4/x3 is a
single binary build unlike other devices that will build unique binaries
for each device. Eventually we will want to remove a lot of the manual
isx3 type stuff from our firmware and go through the boardsupport api
the sdk provides as it will generalize everything into one common system
that any device can support. The upcoming touch branch does a lot of
this for us but this initial PR is JUST to get the sdk swapped over
without any code changes to show seamless integration without any
regressions.

.gitmodules

@@ -1,3 +1,4 @@
-[submodule "open-x4-sdk"]
-	path = open-x4-sdk
-	url = https://github.com/crosspoint-reader/community-sdk.git
+[submodule "freeink-sdk"]
+	path = freeink-sdk
+	url = https://github.com/Free-Ink/freeink-sdk.git
+	branch = main

.skills/SKILL.md

@@ -7,7 +7,7 @@ Mission: Provide a lightweight, high-performance reading experience focused on E
 * Role: Senior Embedded Systems Engineer (ESP-IDF/Arduino-ESP32 specialized).
 * Primary Constraint: 380KB RAM is the hard ceiling. Stability is non-negotiable.
 * Evidence-Based Reasoning: Before proposing a change, you MUST cite the specific file path and line numbers that justify the modification.
-* Anti-Hallucination: Do not assume the existence of libraries or ESP-IDF functions. If you are unsure of an API's availability for the ESP32-C3 RISC-V target, check the open-x4-sdk or official docs first.
+* Anti-Hallucination: Do not assume the existence of libraries or ESP-IDF functions. If you are unsure of an API's availability for the ESP32-C3 RISC-V target, check the freeink-sdk source or the FreeInk SDK docs (https://freeink.org/llms.txt for an LLM-readable index) first.
 * No Unfounded Claims: Do not claim performance gains or memory savings without explaining the technical mechanism (e.g., DRAM vs IRAM usage).
 * Resource Justification: You must justify any new heap allocation (new, malloc, std::vector) or explain why a stack/static alternative was rejected.
 * Verification: After suggesting a fix, instruct the user on how to verify it (e.g., monitoring heap via Serial or checking a specific cache file).
@@ -127,7 +127,7 @@ These flags in `platformio.ini` fundamentally affect firmware behavior:
   * lib/hal/: Hardware Abstraction Layer (HalDisplay, HalGPIO, HalStorage)
   * lib/I18n/: Internationalization (translations in `translations/*.yaml`, generated string tables)
 * src/activities/: UI logic using the Activity Lifecycle (onEnter, loop, onExit)
-* open-x4-sdk/: Low-level SDK (EInkDisplay, InputManager, BatteryMonitor, SDCardManager)
+* freeink-sdk/: Low-level SDK (EInkDisplay, InputManager, BatteryMonitor, SDCardManager)
 * .crosspoint/: SD-based binary cache for EPUB metadata and pre-rendered layout sections
 
 ### Hardware Abstraction Layer (HAL)

bin/clang-format-fix.ps1

@@ -4,7 +4,7 @@
 
 .DESCRIPTION
     Formats all C/C++ source and header files in the repository, excluding
-    generated, vendored, and build directories (open-x4-sdk, builtinFonts,
+    generated, vendored, and build directories (freeink-sdk, builtinFonts,
     hyphenation tries, uzlib, .pio, *.generated.h).
 
     The clang-format binary path is resolved once and cached in
@@ -92,7 +92,7 @@ function Resolve-ClangFormat {
 $clangFormat = Resolve-ClangFormat
 
 $exclude = @(
-    'open-x4-sdk'
+    'freeink-sdk'
     'lib\EpdFont\builtinFonts'
     'lib\Epub\Epub\hyphenation\generated'
     'lib\uzlib'

docs/contributing/architecture.md

@@ -8,7 +8,7 @@ At a high level, it is firmware that uses an activity-driven application archite
 
 ```mermaid
 graph TD
-    A[Hardware: ESP32-C3 + SD + E-ink + Buttons] --> B[open-x4-sdk]
+    A[Hardware: ESP32-C3 + SD + E-ink + Buttons] --> B[freeink-sdk]
     B --> C[lib/hal wrappers]
     C --> D[src/main.cpp runtime loop]
     D --> E[Activities layer]
@@ -195,10 +195,10 @@ When editing related source assets, regenerate via normal build steps/scripts.
 - `src/`: app orchestration, settings/state, and activity implementations
 - `src/network/`: web server and OTA/update networking
 - `src/components/`: theming and shared UI components
-- `lib/hal/`: hardware abstraction wrappers around open-x4-sdk
+- `lib/hal/`: hardware abstraction wrappers around freeink-sdk
 - `lib/Epub/`: EPUB parser, layout, CSS handling, and hyphenation
 - `lib/`: supporting libraries (fonts, text, filesystem helpers, etc.)
-- `open-x4-sdk/`: hardware SDK submodule (display, input, storage, battery)
+- `freeink-sdk/`: hardware SDK submodule (display, input, storage, battery). Docs: https://freeink.org/docs
 - `docs/`: user and technical documentation
 
 ## Embedded constraints that shape design

platformio.ini

@@ -35,6 +35,8 @@ build_flags =
 # Increase PNG scanline buffer to support up to 2048px wide images
 # Default is (320*4+1)*2=2562, we need more for larger images
   -DPNG_MAX_BUFFERED_PIXELS=16416
+  -DFREEINK_DEVICE_X4=1
+  -DFREEINK_DEVICE_X3=1
   -Wno-bidi-chars
   -Wl,--wrap=panic_print_backtrace,--wrap=panic_abort,--wrap=bootloader_common_check_efuse_blk_validity
   -fno-exceptions
@@ -57,10 +59,14 @@ extra_scripts =
 
 ; Libraries
 lib_deps =
-  BatteryMonitor=symlink://open-x4-sdk/libs/hardware/BatteryMonitor
-  InputManager=symlink://open-x4-sdk/libs/hardware/InputManager
-  EInkDisplay=symlink://open-x4-sdk/libs/display/EInkDisplay
-  SDCardManager=symlink://open-x4-sdk/libs/hardware/SDCardManager
+  BatteryMonitor=symlink://freeink-sdk/libs/hardware/BatteryMonitor
+  InputManager=symlink://freeink-sdk/libs/hardware/InputManager
+  EInkDisplay=symlink://freeink-sdk/libs/display/FreeInkDisplay
+  SDCardManager=symlink://freeink-sdk/libs/hardware/SDCardManager
+  BoardConfig=symlink://freeink-sdk/libs/hardware/BoardConfig
+  PowerManager=symlink://freeink-sdk/libs/hardware/PowerManager
+  FreeInkUI=symlink://freeink-sdk/libs/ui/FreeInkUI
+  Icons=symlink://freeink-sdk/libs/assets/Icons
   bblanchon/ArduinoJson @ 7.4.2
   ricmoo/QRCode @ 0.0.1
   bitbank2/PNGdec @ 1.1.6