drivers/bus_i2c_busdev.h: header not self-contained (uses extDevice_t without including drivers/bus.h)

[nerdCopter]

Problem

src/main/drivers/bus_i2c_busdev.h uses extDevice_t and uint8_t in its function prototypes but does not #include "drivers/bus.h" (which defines extDevice_t) or any stdint/platform header. The header compiles only if every caller happens to include drivers/bus.h before drivers/bus_i2c_busdev.h.

// src/main/drivers/bus_i2c_busdev.h
#pragma once

bool i2cBusWriteRegister(const extDevice_t *dev, uint8_t reg, uint8_t data);
bool i2cBusReadRegisterBuffer(const extDevice_t *dev, uint8_t reg, uint8_t *data, uint8_t length);
uint8_t i2cBusReadRegister(const extDevice_t *dev, uint8_t reg);

extDevice_t is defined in drivers/bus.h. uint8_t comes from <stdint.h> (usually pulled in transitively). Neither is made available by this header directly.

Current state (not a bug today)

The existing callers of this header (src/main/drivers/bus_i2c_busdev.c, the three I2C sensor init files) happen to include drivers/bus.h first, so the latent issue doesn't fire. Compilation is clean today.

It did fire transiently during the Stage J I2C bus-resource split refactor (see PR for context, stage branched from #1114): adding the include to sensors/compass.c in the file's existing include-block order (bus_i2c → bus_spi → bus) placed bus_i2c_busdev.h before bus.h, which produced:

./src/main/drivers/bus_i2c_busdev.h:23:31: error: unknown type name 'extDevice_t'

The working fix in the Stage J commit was to reorder the include block in compass.c so bus.h precedes bus_i2c_busdev.h. That workaround is brittle — any future include ordering change or new caller can trigger the same error.

This is a hygiene/forward-compat issue, not a functional bug.

Upstream comparison

Betaflight 4.5-maintenance has the same latent issue in the equivalent header (betaflight/src/main/drivers/bus_i2c_busdev.h is also header-only with no includes). Fixing on our side introduces a minor delta vs BF 4.5; so does leaving it and working around it per-caller. Either is acceptable; the fix is more robust.

Proposed fix

Make the header self-contained:

// src/main/drivers/bus_i2c_busdev.h
#pragma once

#include <stdbool.h>
#include <stdint.h>

#include "drivers/bus.h"

bool i2cBusWriteRegister(const extDevice_t *dev, uint8_t reg, uint8_t data);
...

Sibling consideration: if BF's behavior is preferred for paste-and-tweak alignment, leave the header unchanged but establish a coding-standard convention (documented in AGENTS.md or similar) that drivers/bus.h must precede drivers/bus_i2c_busdev.h in every caller. Less robust than making the header self-contained.

History / origin

Pre-existing since the header was introduced (predates the ongoing extDevice_t refactor). Surfaced during Stage J (I2C bus-resource split) implementation, 2026-04-22. Per the scope-boundary rule established in #1111 review (pre-existing smells get separate issue tickets, not fixes in scoped refactor PRs), filed here for future cleanup.

Acceptance

• drivers/bus_i2c_busdev.h includes drivers/bus.h (directly or via forward-declaration) and compiles cleanly regardless of caller include ordering.
• make test passes.
• Build passes on at least one I2C-heavy target (e.g. any target with a compass or barometer configured).
• Optional: revert the compass.c include-block reordering introduced as the Stage J workaround (harmless to leave).