Direct USB/MTP transport checkpoint

Status

USB_MTP_DETECTION=PASS
MTP_STORAGE_ACCESS=PASS
MTP_ROOT_FOLDER_ACCESS=PASS
MTP_WRITE=PASS
MTP_LIST_FOLDER=PASS
MTP_READ=PASS
MTP_ROUNDTRIP=PASS
MTP_TRANSPORT_FOUNDATION=PASS
JSON_V1_MTP_TRANSFER=NEXT
TRAINLOG_FORMAT_V1=FROZEN

Trainlog now accesses Android file-transfer mode directly through Linux USB/MTP. No GVFS mount, FUSE mount, file-manager mount, or manual mount/unmount cycle is required.

Detection

The discovery layer uses libudev.

Only physical USB devices with:

DEVTYPE=usb_device
ID_MTP_DEVICE=1

are returned.

USB interface children such as 6-1:1.0 are deliberately ignored so one physical phone is never reported several times.

The device record contains:

USB bus number;
USB device number;
vendor/product IDs;
vendor/model strings when available;
serial number when available;
sysfs path.

MTP access

The transport layer uses libmtp.

The udev bus/device pair is matched against libmtp raw devices so Trainlog opens the exact physical phone selected by discovery.

Implemented operations:

enumerate MTP storage areas;
expose capacity and free-space information;
find or create a root folder;
upload a local text file;
list direct children of one MTP folder;
download one MTP file to a local path.

Cached and uncached libmtp opening modes are kept separate because folder-tree operations and direct LIBMTP_Get_Files_And_Folders() traversal have different backend requirements.

Physical validation

The checkpoint was validated against an Android Samsung device in USB "file transfer" / MTP mode.

Observed storage:

description = Stockage interne
storage_id  = 0x00010001
access      = read/write

Trainlog created:

Stockage interne/
└── Trainlog/
    └── trainlog-probe.txt

The probe was then listed, downloaded back to the Linux host, and compared byte-for-byte with the original local content.

Final result:

ROUNDTRIP=PASS Trainlog/trainlog-probe.txt

Boundary

This checkpoint validates the transport foundation only.

It does not yet claim that a real Trainlog JSON v1 session has been transferred or imported.

1. define the Trainlog MTP exchange directory layout
2. transfer a real valid JSON v1 document
3. verify byte-for-byte readback
4. feed the downloaded document to the frozen v1 validator/import path
5. build the minimal Android recorder on top of that contract

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