Readiness line detection can miss due to 1KB buffer boundary

[kKaskak]

At server.rs:90-113, the buffer is 1KB and the parser uses string_data.lines() against a single read. If the "EngineFS server started at" line straddles two reads, neither contains the full line and the check fails. Since endpoint_sent is one-shot, it's never recovered. 60s timeout fires and WebUI gets no server URL. Should buffer partial lines across reads.

[kKaskak]

Verdict: valid.

Current stdout reader scans only the current 1KB chunk with string_data.lines() while appending a separate log buffer. A readiness line split across reads can be missed, and current start() then waits on rx.recv() without timeout. Buffer partial lines or scan the accumulated tail before deciding readiness.