_download_image() and _download_video() both used client.get() +
response.content, buffering the entire media body into memory before
checking the size cap. A server that omits Content-Length could send
an arbitrarily large payload, causing OOM.
Extract _stream_download_to_file() shared helper: streams via
client.stream() + aiter_bytes(), writes chunks to a temp file, enforces
the running byte count against the cap after each chunk, and atomically
replaces onto the destination on success. Cleans up the temp file on
failure. Uses utils.atomic_replace() for cross-device/symlink safety.
Malformed Content-Length values are now caught and ignored instead of
crashing with ValueError; the streaming cap is the authoritative guard.
Approach adapted from PR #10440 by @WuKongAI-CMU (closed as stale —
14923 commits behind, reverted 32 commits of vision_tools.py evolution
including SSRF-safe client, retry classification, and lazy imports).
Closes#10440
b7eb97a835