feat(conversations,api,ui): rewind takes the last turns of a thread back, the cut session stays in the store

tests/test_conversations.py

@@ -504,6 +504,105 @@ async def test_copy_seed_forks_parent_with_window(world: World) -> None:
     assert (await world.conversations.get(child.external_id)).flags["seed"] is None
 
 
+async def _three_turns(world: World) -> tuple[str, list[dict[str, Any]]]:
+    sid = str(uuid.uuid4())
+    history = [
+        {"role": "user", "content": "one"},
+        {"role": "assistant", "content": "done one"},
+        {"role": "user", "content": "two"},
+        {
+            "role": "assistant",
+            "content": [{"type": "tool_use", "id": "t1", "name": "Read", "input": {}}],
+        },
+        {
+            "role": "user",
+            "content": [{"type": "tool_result", "tool_use_id": "t1", "content": "x"}],
+        },
+        {"role": "assistant", "content": "done two"},
+        {"role": "user", "content": "three"},
+        {"role": "assistant", "content": "refused"},
+    ]
+    entries = build_entries(history, session_id=sid, cwd=str(world.root), model="m")
+    entries[-1]["isApiErrorMessage"] = True
+    note = {
+        **entries[2],
+        "uuid": str(uuid.uuid4()),
+        "message": {
+            "role": "user",
+            "content": [{"type": "text", "text": "[Request interrupted by user]"}],
+        },
+    }
+    del note["promptSource"]
+    entries.insert(6, note)
+    await world.store.append(world.key(sid), entries)
+    return sid, entries
+
+
+async def test_rewind_moves_the_thread_to_a_fork_that_ends_before_the_turn(
+    world: World,
+) -> None:
+    sid, entries = await _three_turns(world)
+    conv = await world.conversations.create(
+        kind="master", agent="a", origin="test", session_id=sid
+    )
+    await world.conversations.post(conv, "live")
+    await world.settle(conv, 1)
+    assert world.pool.get(conv.external_id) is not None
+
+    turns = await world.conversations.turns(conv)
+    assert [(t["text"], t["reply"], t["failed"]) for t in turns] == [
+        ("two", "done two", False),
+        ("three", "refused", True),
+    ]
+    assert [t["id"] for t in turns] == [entries[2]["uuid"], entries[7]["uuid"]]
+
+    result = await world.conversations.rewind(conv, turns[1]["id"])
+
+    assert result.turns == 1 and result.previous_session == sid
+    moved = result.conversation.session_id
+    assert moved != sid
+    assert (await world.conversations.get(conv.external_id)).session_id == moved
+    assert await world.store.load(world.key(sid)) == entries
+    kept = [
+        e["message"]["content"]
+        for e in await world.store.load(world.key(moved))
+        if e["type"] in ("user", "assistant")
+    ]
+    assert len(kept) == 7 and kept[0] == "one"
+    assert kept[-1] == [{"type": "text", "text": "[Request interrupted by user]"}]
+    assert world.pool.get(conv.external_id) is None
+
+    await world.conversations.run_text_turn(conv, "after", origin="user")
+    assert conv.session_id == sid
+    assert ScriptedClient.instances[-1].options.resume == moved
+
+    (two,) = await world.conversations.turns(result.conversation)
+    assert two["text"] == "two"
+    again = await world.conversations.rewind(conv, two["id"])
+    assert again.turns == 1 and again.previous_session == moved
+    assert await world.conversations.turns(again.conversation) == []
+    first = (await world.store.load(world.key(again.conversation.session_id)))[0]
+    with pytest.raises(LookupError):
+        await world.conversations.rewind(conv, first["uuid"])
+    with pytest.raises(LookupError):
+        await world.conversations.rewind(conv, str(uuid.uuid4()))
+
+
+async def test_rewind_waits_for_no_turn(world: World) -> None:
+    sid, entries = await _three_turns(world)
+    conv = await world.conversations.create(
+        kind="master", agent="a", origin="test", session_id=sid
+    )
+    ScriptedClient.hold = asyncio.Event()
+    await world.conversations.post(conv, "busy")
+    await asyncio.sleep(0.2)
+    with pytest.raises(RuntimeError, match="mid-turn"):
+        await world.conversations.rewind(conv, entries[7]["uuid"])
+    ScriptedClient.hold.set()
+    await world.settle(conv, 1)
+    assert (await world.conversations.get(conv.external_id)).session_id == sid
+
+
 async def test_merge_injects_summary_into_parent(world: World) -> None:
     sid = str(uuid.uuid4())
     await world.store.append(