Offload image prepare to executor, keep BLE transfer on the loop

[balloob]

Problem

_async_send_image (the shared upload path behind both the upload_image and drawcustom services) awaited device.upload_image(...). Inside the library that call runs _prepare_image synchronously on the event loop: rotate + fit + dither + encode + zlib on a full frame. So every upload/drawcustom blocked the Home Assistant event loop for the entire CPU stage before any BLE I/O even started.

Fix

py-opendisplay 7.9.0 exposes the split deliberately:

• prepare_image(image, config=..., ...) — module-level, does the heavy CPU work (rotate/fit/dither/encode/compress) from the device config only, no BLE connection.
• device.upload_prepared_image(prepared, refresh_mode=...) — sends the pre-computed data over BLE.

_async_send_image now runs prepare_image in the executor via hass.async_add_executor_job (passing the same dither_mode/tone/fit/rotate options previously handed to upload_image), then does only upload_prepared_image on the loop inside _async_connect_and_run. The heavy CPU work is off the loop; only the BLE transfer stays on it.

compress is gated on display.supports_zip, mirroring upload_image() which passes compress and supports_compression into _prepare_image. When the panel has no zip support, prepare_image() returns compressed_data=None and upload_prepared_image() falls back to the uncompressed protocol — identical behavior to before, just moved off-loop.

Interaction with the per-MAC ble_lock (#53)

This is written so the two compose correctly. #53 wraps the whole _async_connect_and_run connection lifetime (async with entry.runtime_data.ble_lock, OpenDisplayDevice(...)) in the BLE lock. By moving the prepare_image executor call before _async_connect_and_run (before the connection is opened), the CPU work runs outside the lock, and the lock is held only around the upload_prepared_image BLE transfer — exactly the desired scoping (don't hold the per-tag BLE lock while burning CPU on dithering). #53 is not yet merged into feat/clean-port; this branch is based on the current feat/clean-port state and does not touch the lock itself, so it merges cleanly in either order.

Testing

• python -m py_compile custom_components/opendisplay/services.py passes.
• Verified the v7.9.0 API by signature: prepare_image is a module-level function exported from opendisplay, deriving capabilities and panel_ic_type from config when not supplied (equivalent to a config-constructed device that skips interrogation); upload_prepared_image(prepared_data, refresh_mode=..., compress=True, ...) accepts the (uncompressed, compressed_or_None, processed_image) tuple prepare_image returns. Only args that exist at the pinned v7.9.0 are used.
• Reasoned end-to-end: the dither/encode/zlib CPU stage now runs in an executor thread; the BLE transfer stays on the loop.

🤖 Generated with Claude Code

https://claude.ai/code/session_012g2e8mr132vcizx92WsgiR