Status: removed. s += "x" versus String::with_capacity was about 1.00× at N=500000. A 32-byte chunk was about 1.05×. A tiny repeated builder was about 2.04×, which is fixed overhead on a short string, not the hot fill. format! rebind stays rs-format-rebind-hot. No matcher.

Slug never reused.
Historical JSONL and the note stay beside this file. Fixtures are under _removed/fixtures/.

A later quiet rustc 1.99 pair, load 0.03 then 0.11, was 1.042× and 1.026× on 500000 push_str("x") calls. The removal stays.

rs-string-plus-in-loop — removed 2026-10-23 (Asia/Shanghai)