Crosspoint/.claude/skills/hal-and-abstractions/SKILL.md

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hal-and-abstractions

Layering and abstraction discipline for the firmware. Use when touching storage, input, display, settings, i18n, or rendering, or any code that could reach into the SDK. Covers routing through the HAL (HalStorage / HalGPIO / HalDisplay) instead of raw SDK classes, MappedInputManager logical buttons instead of raw GPIO indices, UITheme/GUI for all rendering, the singleton macros, tr() for user-facing text, and where a new abstraction boundary belongs.

HAL and Abstractions

CLAUDE.md lists the HAL classes and the SdFat-concurrency reason they exist. This is when and how to route through them, and where to draw a new boundary.

Route through the layer, always

• SD card I/O: Storage (HalStorage) and HalFile. Never SdFat, FsFile, SdSpiCard, FsBaseFile, or SDCardManager directly. The HAL serializes every SD access through one mutex; bypassing it races the SPI state machine and panics FreeRTOS (CLAUDE.md has the failure mode). This is a correctness boundary, not a style preference.
• Display: HalDisplay over EInkDisplay. Input: HalGPIO over InputManager.
• Rendering: everything through the GUI macro (UITheme) and the renderer's oriented metrics. No hardcoded fonts, colors, coordinates, or 800/480 literals; ask the renderer for width/height and use the oriented viewable area.
• Input in activities: MappedInputManager::Button logical enums (Button::Confirm, Button::PageForward, ...). Never raw HalGPIO::BTN_* indices outside ButtonRemapActivity. Logical buttons survive user remapping and orientation; raw indices do not.
• Shared state: the singleton macros (SETTINGS, APP_STATE, GUI, Storage, I18N), not threaded pointers.

User-facing text

Every string a user reads goes through tr(STR_*). Add the key to the English YAML, regenerate with scripts/gen_i18n.py, then use the StrId. Log lines (LOG_*) stay hardcoded.

Drawing a new boundary

When you need an SDK capability the HAL does not expose yet, add the method to the HAL; do not reach around it. The new method inherits the mutex, logging, and error contract the rest of the HAL carries. A one-off direct SDK call in an activity is exactly the layering violation the mutex discipline cannot tolerate.

Keep abstractions thin. A wrapper that only renames an SDK call without adding the mutex, logging, or an error contract is dead weight. Add a layer only when it carries one of those contracts or hides a real implementation choice.

Self-review

• No direct SdFat / FsFile / SDCardManager / EInkDisplay / InputManager use outside lib/hal.
• File access uses HalFile; no .close() on a local handle (DESTRUCTOR_CLOSES_FILE); members closed in onExit.
• Input uses MappedInputManager::Button, not raw BTN_* indices.
• Rendering goes through GUI/UITheme and oriented metrics; no 800/480 or hardcoded fonts/coords.
• User-facing strings use tr(STR_*); new keys added to YAML and regenerated.
• Any new SDK capability is exposed as a HAL method, not called inline.