Port from openclaw/openclaw#95108: an unbounded response.read() on a
non-OK *streaming* response can balloon memory (huge body) or hang the
agent forever (body opens then stalls with no further bytes). The
diagnostic body is only ever shown truncated, so reading megabytes or
blocking indefinitely buys nothing.
Add agent/bounded_response.read_streaming_error_body() which caps the
read at a byte limit and enforces a hard wall-clock deadline (run on a
worker thread so it can interrupt a socket read that stalls mid-chunk,
which a between-chunk wall-clock check cannot). Wire it into all three
streaming error-body sites that previously did a bare response.read():
native Gemini, Gemini Cloud Code, and Antigravity Cloud Code. The
existing error builders now accept an optional pre-read body_text so
classification (status code, RESOURCE_EXHAUSTED, free-tier guidance,
Retry-After) is preserved unchanged.
Tests use a real in-process socket server (no mocks): oversize body is
capped, stalled body hits the deadline with partial text preserved,
normal error envelope reads intact and parses.
