http.js:640:3E stores a POST's report line in st.flash, and http.js:773:3E spends
it into the NEXT HTML page painted — by whichever connection asks first.
Another tab or client steals the poster's report; the poster sees nothing.
BEE-055 fixed the replay-from-cache half (bubble + no-store) but the flash
slot stayed server-global. Found in the 2026-08-21 review.
Bind the report to the posting request — ride the 303 (query param the next paint spends) or per-connection state — with a two-client repro test.