File locking refactored (#631)

Remove FileMutex and wire locking into driver subsystems.

Platforms/platform-esp32/include/tactility/drivers/esp32_sdcard.h

@@ -2,6 +2,7 @@
 #pragma once
 
 #include <sd_protocol_types.h>
+#include <tactility/error.h>
 
 #ifdef __cplusplus
 extern "C" {
@@ -16,6 +17,27 @@ struct Device;
  */
 sdmmc_card_t* esp32_sdcard_get_card(struct Device* device);
 
+/**
+ * @brief Wraps the card's do_transaction function pointer so every SD command takes the parent
+ * SPI controller's bus lock.
+ * @param[in] device the SD card device
+ * @param[in] card the card returned by the mount call, passed directly rather than re-resolved
+ *     via esp32_sdcard_get_card(): this is called from within the driver's own start_device
+ *     callback, before device_is_ready() is true, so the readiness-gated getters can't be used
+ *     here.
+ * @retval ERROR_NONE on success, or when the device's parent is not a SPI controller (no-op,
+ *     e.g. SDMMC cards, which have no shared bus to arbitrate)
+ */
+error_t esp32_sdcard_install_bus_lock(struct Device* device, sdmmc_card_t* card);
+
+/**
+ * @brief Removes the bus lock installed by esp32_sdcard_install_bus_lock(), restoring the card's
+ * original do_transaction. No-op if no lock was installed for this device. Must be called before
+ * the card handle is freed.
+ * @param[in] device the SD card device
+ */
+void esp32_sdcard_remove_bus_lock(struct Device* device);
+
 #ifdef __cplusplus
 }
 #endif