`truncate_before_user_ordinal` is an index into the list of *real* user
turns. The gateway builds that list with `role == "user" and not
display_kind`, and `test_prompt_submit_truncate_ordinal_skips_display_kind_rows`
already pins why: "Without the filter, a trailing marker shifts the ordinal
so the wrong message is targeted for truncation."
`_apply_personality_to_session` broke that invariant at the producer. Its
pivot marker rides as `role=user` — deliberately, so strict
OpenAI-compatible providers accept it mid-conversation (the same reason
`_append_model_switch_marker` does) — but unlike the model-switch marker it
carried no `display_kind`. The gateway therefore counted it as a real user
turn while no client ever renders it as one.
After a personality change the two sides address different lists: every
later rewind/edit/regenerate resolves one slot too early, and
`replace_messages()` hard-DELETEs the extra span. That is the reported
signature — an in-range, valid ordinal, `confirm_truncate: true`, and a cut
that moved backwards with no user rewind action.
Tag the pivot like the model-switch marker, and teach the desktop to
project the kind as a timeline row so a persisted marker is never rendered
— or counted — as a user turn on the client side either. Both ends must
exclude it; excluding it on only one end just inverts the drift.
The regression test drives the real injection point rather than a
hand-written marker dict. Without the fix it fails with "the pivot shifted
the ordinal: the cut landed at 3 instead of 5", losing a turn the user
never asked to drop.
Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
joaomarcos
abd85a94bc