test(tui): cover empty truncate guard on prompt.submit

Refuse ordinal-0 wipes without confirm_empty_truncate; allow the
opt-in path used by first-turn restore/regenerate.

apps/desktop/src/app/session/hooks/use-prompt-actions/index.test.tsx

@@ -1450,7 +1450,8 @@ describe('usePromptActions restoreToMessage', () => {
       {
         session_id: RUNTIME_SESSION_ID,
         text: 'first prompt',
-        truncate_before_user_ordinal: 0
+        truncate_before_user_ordinal: 0,
+        confirm_empty_truncate: true
       },
       1_800_000
     )
@@ -1517,7 +1518,8 @@ describe('usePromptActions restoreToMessage', () => {
       {
         session_id: RUNTIME_SESSION_ID,
         text: 'first prompt',
-        truncate_before_user_ordinal: 0
+        truncate_before_user_ordinal: 0,
+        confirm_empty_truncate: true
       },
       1_800_000
     )
@@ -1562,7 +1564,8 @@ describe('usePromptActions restoreToMessage', () => {
       {
         session_id: RUNTIME_SESSION_ID,
         text: 'first prompt',
-        truncate_before_user_ordinal: 0
+        truncate_before_user_ordinal: 0,
+        confirm_empty_truncate: true
       },
       1_800_000
     )

apps/desktop/src/app/session/hooks/use-prompt-actions/rewind.test.ts

@@ -0,0 +1,19 @@
+import { describe, expect, it } from 'vitest'
+
+import { truncateSubmitParams } from './rewind'
+
+describe('truncateSubmitParams', () => {
+  it('omits truncation fields when no ordinal is set', () => {
+    expect(truncateSubmitParams(undefined)).toEqual({})
+  })
+
+  it('requires confirm_empty_truncate only for ordinal 0', () => {
+    expect(truncateSubmitParams(0)).toEqual({
+      truncate_before_user_ordinal: 0,
+      confirm_empty_truncate: true
+    })
+    expect(truncateSubmitParams(1)).toEqual({
+      truncate_before_user_ordinal: 1
+    })
+  })
+})

tests/test_tui_gateway_server.py

@@ -3239,6 +3239,145 @@ def test_prompt_submit_rejects_negative_truncate_ordinal(monkeypatch):
         server._sessions.pop("trunc-sid", None)
 
 
+def test_prompt_submit_refuses_empty_truncation_without_confirm(monkeypatch):
+    """Stale truncate_before_user_ordinal=0 must not wipe a non-empty transcript.
+
+    Desktop desync can attach ordinal 0 to an ordinary fresh submit. That cuts
+    at the first user message (history[:0] == []) and replace_messages() would
+    DELETE every durable row. Refuse unless confirm_empty_truncate is set.
+    """
+    replaced = []
+
+    class _FakeDB:
+        def replace_messages(self, key, messages):
+            replaced.append((key, list(messages)))
+
+    history = [
+        {"role": "user", "content": "first"},
+        {"role": "assistant", "content": "ok"},
+        {"role": "user", "content": "second"},
+        {"role": "assistant", "content": "done"},
+    ]
+    server._sessions["empty-trunc-sid"] = _session(history=list(history))
+    monkeypatch.setattr(server, "_get_db", lambda: _FakeDB())
+    monkeypatch.setattr(
+        server, "_start_agent_build", lambda *a, **k: pytest.fail("must not start a turn")
+    )
+    monkeypatch.setattr(
+        server, "_start_inflight_turn", lambda *a, **k: pytest.fail("must not start a turn")
+    )
+
+    try:
+        # Missing confirm → refuse.
+        resp = server.handle_request(
+            {
+                "id": "1",
+                "method": "prompt.submit",
+                "params": {
+                    "session_id": "empty-trunc-sid",
+                    "text": "fresh typed message",
+                    "truncate_before_user_ordinal": 0,
+                },
+            }
+        )
+        assert resp["error"]["code"] == 4025
+        assert "confirm_empty_truncate" in resp["error"]["message"]
+        # Explicit falsey values must not satisfy the opt-in either.
+        for falsey in (False, 0, "", "false", "no"):
+            resp = server.handle_request(
+                {
+                    "id": "1",
+                    "method": "prompt.submit",
+                    "params": {
+                        "session_id": "empty-trunc-sid",
+                        "text": "fresh typed message",
+                        "truncate_before_user_ordinal": 0,
+                        "confirm_empty_truncate": falsey,
+                    },
+                }
+            )
+            assert resp["error"]["code"] == 4025, falsey
+        assert server._sessions["empty-trunc-sid"]["history"] == history
+        assert server._sessions["empty-trunc-sid"]["running"] is False
+        assert server._sessions["empty-trunc-sid"]["history_version"] == 0
+        assert replaced == []
+    finally:
+        server._sessions.pop("empty-trunc-sid", None)
+
+
+def test_prompt_submit_empty_truncation_allowed_with_confirm(monkeypatch):
+    """Intentional restore/regenerate of the first user turn may wipe history."""
+
+    seen = {}
+    replaced = []
+
+    class _Agent:
+        def run_conversation(
+            self, prompt, conversation_history=None, stream_callback=None
+        ):
+            seen["prompt"] = prompt
+            seen["history"] = conversation_history
+            return {
+                "final_response": "regenerated",
+                "messages": [
+                    *(conversation_history or []),
+                    {"role": "user", "content": prompt},
+                    {"role": "assistant", "content": "regenerated"},
+                ],
+            }
+
+    class _ImmediateThread:
+        def __init__(self, target=None, daemon=None):
+            self._target = target
+
+        def start(self):
+            self._target()
+
+    class _FakeDB:
+        def replace_messages(self, key, messages):
+            replaced.append((key, list(messages)))
+
+    history = [
+        {"role": "user", "content": "first"},
+        {"role": "assistant", "content": "ok"},
+        {"role": "user", "content": "second"},
+        {"role": "assistant", "content": "done"},
+    ]
+    server._sessions["confirm-empty-sid"] = _session(
+        agent=_Agent(), history=list(history)
+    )
+
+    try:
+        monkeypatch.setattr(server.threading, "Thread", _ImmediateThread)
+        monkeypatch.setattr(server, "_get_usage", lambda _a: {})
+        monkeypatch.setattr(server, "render_message", lambda _t, _c: "")
+        monkeypatch.setattr(server, "_emit", lambda *a: None)
+        monkeypatch.setattr(server, "_get_db", lambda: _FakeDB())
+
+        resp = server.handle_request(
+            {
+                "id": "1",
+                "method": "prompt.submit",
+                "params": {
+                    "session_id": "confirm-empty-sid",
+                    "text": "first",
+                    "truncate_before_user_ordinal": 0,
+                    "confirm_empty_truncate": True,
+                },
+            }
+        )
+        assert resp.get("result"), f"got error: {resp.get('error')}"
+        assert seen["prompt"] == "first"
+        assert seen["history"] == []
+        assert replaced == [("session-key", [])]
+        assert server._sessions["confirm-empty-sid"]["history"] == [
+            {"role": "user", "content": "first"},
+            {"role": "assistant", "content": "regenerated"},
+        ]
+    finally:
+        server._sessions.pop("confirm-empty-sid", None)
+
+
 class _StopAfterOneNotificationPoll:
     def __init__(self):
         self._checks = 0