A batch carries the Mattermost user id of each message; the turn's speaker
is the username of the one user who wrote all of it (Client::username,
kept in a map on the event loop), and None for two or more people or a
failed lookup. The turn's text is unchanged.
Checks: reference replayed from the task text on a fresh ref-02 worktree
with its own build dir, byte-identical; make gate ok with 1148 tests
(1138 + 10); /tmp unchanged around both gate runs; 21 mutations, all
caught; new tests stressed 40 times under load, no failure; every before
block found once at ref 02; no chat-template tags.
Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>
