fix(acp): clear stale interrupted prompt when a new turn starts

acp_adapter/server.py

@@ -1383,6 +1383,13 @@ async def prompt(
                 return PromptResponse(stop_reason="end_turn")
             state.is_running = True
             state.current_prompt_text = user_text or "[Image attachment]"
+            # A real turn is starting, so any prompt salvaged for a later
+            # /steer after a prior client cancel is now stale — the user moved
+            # on to this turn. Drop it so a /steer on a future idle session
+            # can't resurrect an abandoned prompt. The /steer salvage path
+            # above already consumed and cleared it before reaching here, so
+            # this only discards a value left by an intervening completed turn.
+            state.interrupted_prompt_text = ""
 
         logger.info("Prompt on session %s: %s", session_id, user_text[:100])
 

tests/acp_adapter/test_acp_commands.py

@@ -147,6 +147,39 @@ async def test_acp_steer_after_zed_interrupt_replays_interrupted_prompt_with_gui
     assert state.interrupted_prompt_text == ""
 
 
+@pytest.mark.asyncio
+async def test_acp_normal_turn_clears_stale_interrupted_prompt():
+    """A completed normal turn must not leave a salvageable prompt behind.
+
+    Regression: interrupted_prompt_text is set only on a running-cancel and
+    cleared only inside the /steer salvage path. If the user cancels a
+    running turn, then sends an ordinary prompt (which runs to completion),
+    the interrupted prompt was never cleared — so a later /steer on the idle
+    session would resurrect and re-run the task the user cancelled and moved
+    on from. Starting any real turn must drop the stale salvage buffer.
+    """
+    acp_agent, state, fake, _conn = make_agent_and_state()
+    # Left over from a prior running-cancel of "refactor the auth module".
+    state.interrupted_prompt_text = "refactor the auth module"
+
+    # An ordinary prompt runs to completion in between.
+    await acp_agent.prompt(
+        session_id=state.session_id,
+        prompt=[TextContentBlock(type="text", text="what's the weather")],
+    )
+    assert state.interrupted_prompt_text == ""
+    assert fake.runs == ["what's the weather"]
+
+    # Now /steer on the idle session must run ONLY the steer text, not the
+    # abandoned prompt.
+    fake.runs.clear()
+    await acp_agent.prompt(
+        session_id=state.session_id,
+        prompt=[TextContentBlock(type="text", text="/steer be concise")],
+    )
+    assert fake.runs == ["be concise"]
+
+
 @pytest.mark.asyncio
 async def test_acp_steer_on_idle_session_runs_as_regular_prompt():
     # /steer on an idle session (no running turn, nothing to salvage) should