Status: removed. The id is not reused. A quiet-enough zig c++ -O2 pair on linux x64, load 1.94, filled 500000 ints: push_back without reserve was 2.012× and 2.058×. An earlier pair at load 2.18 was 2.12× and 2.89× with a wide grow side. The same runs pushed one character onto a std::string 200000 times and reserve was slower (0.824× and 0.794×). A line matcher cannot tell those apart, so the check stays deleted.

No semantic slug was assigned; do not reuse CX001 or invent a replacement id with the same number.
Matcher deleted; historical JSONL (if any) kept beside this note.

CX001 — removed 2026-10-22 (Asia/Shanghai)