Record how the import sync tells its own writes apart

The reasoning belongs where somebody would look before changing the poll:
status is the obvious discriminator and is wrong, and the failure it
produces reads as the model repeating itself rather than as a bug.

AGENTS.md

@@ -41,6 +41,14 @@ repo is in PLAN.md's "Backend layout" section.
   `POST /setups`. Only the tail is replayed (`REPLAY_LINES`) because these
   files reach tens of megabytes and the CLI reads the real one itself; what
   crosses the tunnel is what a person reads, not what the model is given.
+  An imported session then **keeps itself level with that file**, so work
+  done at a terminal appears without anyone pressing anything. `--resume`
+  appends to the same transcript rather than forking (measured), so the
+  only hard question is which new lines came from *here* — answered by
+  counting the events this session has recorded, not by looking at its
+  status. Status is the obvious signal and is wrong: a turn that starts and
+  finishes between two polls reads as idle at both, and its own output gets
+  replayed on top of itself. That bug was visible on screen as `donedone`.
 - `server/src/models.rs` — downloaded GGUF models and the HuggingFace
   browsing behind them. Downloads are keyed by the model rather than by
   who asked, so any device can watch one; they resume through HTTP Range,