Read the resolved partition-table file in upload_program before opening
a network connection. Reject anything that isn't 0xC00 bytes, doesn't
start with ESP_PARTITION_MAGIC, or is missing the MD5 checksum entry, so
mistakes (wrong file, swapped --file path) surface as a local error
instead of a post-handshake OTA_RESPONSE_ERROR_PARTITION_TABLE_VERIFY.
Includes unit tests covering size, magic, md5-presence, missing-file,
and end-to-end upload_program rejection, plus three real partition
tables checked in as fixtures (ESPHome build, ESP-IDF Hello-world,
esphome_dashboard prebuilt).
J. Nick Koston
51c5500809