fix(core): stop interactive runs stalling on a missing tool call

Interactive turns ended by plain text left the agent parked in 'waiting'
forever. Require an explicit lifecycle tool in both modes and nudge a
text-only turn back into a tool call, bounded by a recovery limit.

strix/agents/prompts/system_prompt.jinja

@@ -31,19 +31,16 @@ INTER-AGENT MESSAGES:
 
 {% if interactive %}
 INTERACTIVE BEHAVIOR:
-- You are in an interactive conversation with a user
-- CRITICAL: A message WITHOUT a tool call IMMEDIATELY STOPS your entire execution and waits for user input. This is a HARD SYSTEM CONSTRAINT, not a suggestion.
-  - Statements like "Planning the assessment..." or "I'll now scan..." or "Starting with..." WITHOUT a tool call will HALT YOUR WORK COMPLETELY. The system interprets no-tool-call as "I'm done, waiting for the user."
-  - If you want to plan, call the think tool. If you want to act, call the appropriate tool. There is NO valid reason to output text without a tool call while working on a task.
-  - The ONLY time you may send a message without a tool call is when you are genuinely DONE and presenting final results, or when you NEED the user to answer a question before continuing.
-- EVERY message while working MUST contain exactly one tool call — this is what keeps execution moving. No tool call = execution stops.
-- You may include brief explanatory text BEFORE the tool call
-- Respond naturally when the user asks questions or gives instructions
-- For simple conversation, acknowledgements, or direct questions that you can answer from current context, reply in plain text and stop. Do NOT call think just to prepare wording.
-- If you use a tool to answer a user question (for example list_todos, view_agent_graph, or a file read), then after the tool result arrives, provide the answer in plain text and stop unless the user explicitly asked you to continue working.
-- Never loop through think or other tools just to prepare, polish, confirm, or announce a final answer. Once you know the answer, say it.
-- NEVER send empty messages — if you have nothing to do or say, call the wait_for_message tool
-- If you catch yourself about to describe multiple steps without a tool call, STOP and call the think tool instead
+- You are in an interactive conversation with a user.
+- HOW EXECUTION ENDS: your turn ends ONLY when you make an explicit lifecycle tool call. Plain text NEVER ends your turn and NEVER hands control to the user — text is shown to the user, and then execution continues.
+  - To hand control back to the user (you answered them, or you need their input before continuing), call the wait_for_message tool. This is the ONLY sanctioned way to yield to the user; it parks you until the user's next message arrives.
+  - To end the whole engagement, call the lifecycle tool: finish_scan (root) or agent_finish (subagent).
+  - A turn that ends with plain text and no tool call does NOT stop you: the system nudges you to continue and will re-run you. Do not rely on going silent to pause — it will not pause you.
+- Answering a user question: put your answer in text, then call wait_for_message in the SAME turn (the text is delivered to the user and you park for their reply). Do not answer and then fall silent — that just triggers a continuation nudge.
+- You may include brief explanatory text before a tool call.
+- Respond naturally when the user asks questions or gives instructions.
+- While actively working on a task, every turn should carry exactly one tool call — use think to plan, the appropriate tool to act, and wait_for_message only when you genuinely need the user.
+- Never loop through think or other tools just to prepare, polish, confirm, or announce an answer. Once you know the answer, say it (then wait_for_message).
 {% else %}
 AUTONOMOUS BEHAVIOR:
 - Work autonomously by default

strix/core/execution.py

@@ -208,22 +208,8 @@ async def run_agent_loop(
         await coordinator.send(agent_id, _reserve_notice())
 
     if not (start_parked and interactive):
-        if interactive:
         with contextlib.suppress(BudgetPausedError):
-                result = await _run_cycle_parked(
-                    agent,
-                    coordinator,
-                    agent_id,
-                    input_data=first_cycle_input,
-                    run_config=run_config,
-                    context=context,
-                    max_turns=max_turns,
-                    session=session,
-                    event_sink=event_sink,
-                    hooks=hooks,
-                )
-        else:
-            result = await _run_noninteractive_until_lifecycle(
+            result = await _run_until_lifecycle(
                 agent,
                 coordinator,
                 agent_id,
@@ -232,6 +218,7 @@ async def run_agent_loop(
                 context=context,
                 max_turns=max_turns,
                 session=session,
+                interactive=interactive,
                 event_sink=event_sink,
                 hooks=hooks,
             )
@@ -268,15 +255,16 @@ async def run_agent_loop(
 
         await coordinator.consume_pending(agent_id)
         with contextlib.suppress(BudgetPausedError):
-            result = await _run_cycle_parked(
+            result = await _run_until_lifecycle(
                 agent,
                 coordinator,
                 agent_id,
-                input_data=[],
+                initial_input=[],
                 run_config=run_config,
                 context=context,
                 max_turns=max_turns,
                 session=session,
+                interactive=True,
                 event_sink=event_sink,
                 hooks=hooks,
             )
@@ -427,7 +415,10 @@ async def respawn_subagents(
                 await coordinator.set_status(child_id, "crashed")
 
 
-async def _run_noninteractive_until_lifecycle(
+_INTERACTIVE_TOOL_RECOVERY_LIMIT = 3
+
+
+async def _run_until_lifecycle(
     agent: Any,
     coordinator: AgentCoordinator,
     agent_id: str,
@@ -437,14 +428,21 @@ async def _run_noninteractive_until_lifecycle(
     context: dict[str, Any],
     max_turns: int,
     session: Session | None,
+    interactive: bool,
     event_sink: StreamEventSink | None,
     hooks: RunHooks[dict[str, Any]] | None,
 ) -> RunResultBase | None:
-    """Non-chat mode keeps running until finish_scan / agent_finish settles status."""
+    """Drive an agent until an explicit lifecycle tool settles its status.
+
+    A turn that ends without ``finish_scan``, ``agent_finish``, or
+    ``wait_for_message`` leaves the agent ``running``: plain text never
+    terminates a run and never yields to the user. Such a turn is nudged back
+    into a tool call, bounded by a recovery limit.
+    """
     result: RunResultBase | None = None
     input_data: Any = initial_input
-    invalid_final_outputs = 0
-    invalid_final_output_limit = max(1, max_turns)
+    recoveries = 0
+    recovery_limit = _INTERACTIVE_TOOL_RECOVERY_LIMIT if interactive else max(1, max_turns)
 
     while True:
         if coordinator.budget_stopped:
@@ -455,6 +453,20 @@ async def _run_noninteractive_until_lifecycle(
             await coordinator.set_status(agent_id, "stopped")
             raise SubagentBudgetReservedError("scan reached the sub-agent budget reserve")
 
+        if interactive:
+            result = await _run_cycle_parked(
+                agent,
+                coordinator,
+                agent_id,
+                input_data=input_data,
+                run_config=run_config,
+                context=context,
+                max_turns=max_turns,
+                session=session,
+                event_sink=event_sink,
+                hooks=hooks,
+            )
+        else:
             result = await _run_cycle(
                 agent,
                 coordinator,
@@ -473,30 +485,55 @@ async def _run_noninteractive_until_lifecycle(
         if status != "running":
             return result
 
-        invalid_final_outputs += 1
+        recoveries += 1
         logger.warning(
-            "agent %s produced non-lifecycle final output in non-interactive mode; "
+            "agent %s ended a turn without a lifecycle tool call (interactive=%s); "
             "forcing tool continuation (%d/%d): %s",
             agent_id,
-            invalid_final_outputs,
-            invalid_final_output_limit,
+            interactive,
+            recoveries,
+            recovery_limit,
             _final_output_preview(result),
         )
 
-        if invalid_final_outputs >= invalid_final_output_limit:
+        if recoveries >= recovery_limit:
+            return await _exhausted_recovery(coordinator, agent_id, result, interactive=interactive)
+
+        input_data = await _append_tool_required_message(
+            session=session,
+            context=context,
+            attempt=recoveries,
+            limit=recovery_limit,
+            interactive=interactive,
+        )
+
+
+async def _exhausted_recovery(
+    coordinator: AgentCoordinator,
+    agent_id: str,
+    result: RunResultBase | None,
+    *,
+    interactive: bool,
+) -> RunResultBase | None:
+    """Settle an agent that never recovered into a tool call.
+
+    Interactive runs park instead of dying: a human is present, so the scan
+    stays resumable by sending another message. Autonomous runs have nobody to
+    resume them, so they fail loudly.
+    """
+    if not interactive:
         await coordinator.set_status(agent_id, "crashed")
         await _notify_parent_on_terminal(coordinator, agent_id, "crashed")
         raise MaxTurnsExceeded(
-                "Agent exhausted non-interactive recovery attempts without calling "
-                "finish_scan or agent_finish."
+            "Agent exhausted recovery attempts without calling finish_scan or agent_finish."
         )
 
-        input_data = await _append_noninteractive_tool_required_message(
-            session=session,
-            context=context,
-            attempt=invalid_final_outputs,
-            limit=invalid_final_output_limit,
+    logger.warning(
+        "agent %s exhausted tool-call recovery attempts; parking until a message arrives",
+        agent_id,
     )
+    await coordinator.set_status(agent_id, "waiting")
+    return result
 
 
 _WAITING_AUTO_RESUME_TIMEOUT_S = 600.0
@@ -724,27 +761,9 @@ async def _run_cycle(  # noqa: PLR0912, PLR0915
             await _notify_parent_on_terminal(coordinator, agent_id, status)
             return None
         else:
-            await _settle_run_result(coordinator, agent_id, interactive)
             return cast("RunResultBase | None", stream)
 
 
-async def _settle_run_result(
-    coordinator: AgentCoordinator,
-    agent_id: str,
-    interactive: bool,
-) -> None:
-    async with coordinator._lock:
-        current_status = coordinator.statuses.get(agent_id)
-
-    if current_status != "running":
-        return
-
-    if not interactive:
-        return
-
-    await coordinator.set_status(agent_id, "waiting")
-
-
 async def _agent_status(coordinator: AgentCoordinator, agent_id: str) -> Status | None:
     async with coordinator._lock:
         return coordinator.statuses.get(agent_id)
@@ -760,18 +779,31 @@ def _final_output_preview(result: RunResultBase | None) -> str:
     return text[:300]
 
 
-async def _append_noninteractive_tool_required_message(
+async def _append_tool_required_message(
     *,
     session: Session | None,
     context: dict[str, Any],
     attempt: int,
     limit: int,
+    interactive: bool,
 ) -> list[dict[str, str]]:
     finish_tool = "finish_scan" if context.get("parent_id") is None else "agent_finish"
+    if interactive:
         message = (
-        "Your previous response ended the autonomous Strix run without a lifecycle tool call. "
-        "That is invalid in non-interactive mode; plain text final answers are ignored. "
-        "Continue immediately and call exactly one tool. "
+            "Your previous message ended a turn without a tool call. Plain text never ends "
+            "execution and never hands control to the user: it is shown to the user, and the "
+            "run continues. Continue immediately and call exactly one tool. "
+            "If you have finished responding and want the user's next message, call "
+            "wait_for_message. "
+            f"If the whole engagement is complete, call {finish_tool}. "
+            "Otherwise use the appropriate execution or planning tool. "
+            f"This is recovery attempt {attempt}/{limit}."
+        )
+    else:
+        message = (
+            "Your previous response ended the autonomous Strix run without a lifecycle tool "
+            "call. That is invalid in non-interactive mode; plain text final answers are "
+            "ignored. Continue immediately and call exactly one tool. "
             f"If your work is complete, call {finish_tool}. "
             "If you are blocked waiting for another agent, call wait_for_message. "
             "Otherwise use the appropriate execution or planning tool. "

strix/tools/agents_graph/tools.py

@@ -232,11 +232,19 @@ async def wait_for_message(  # noqa: PLR0911
     message arrives, so pick a ``timeout_seconds`` proportional to the
     work you're awaiting.
 
+    In an interactive/chat session this is also the ONLY sanctioned way
+    to hand control back to the user: plain text does not end your turn
+    or yield to the user, so after you answer the user (or when you need
+    their input before continuing) call this to park until their next
+    message arrives.
+
     **Critical caveats:**
 
-    - **Never** call this if you finished your own task and have **no**
-      child agents running — that's a permanent stall. Call
-      ``finish_scan`` (root) or ``agent_finish`` (subagent) instead.
+    - In an autonomous (non-interactive) run, **never** call this if you
+      finished your own task and have **no** child agents running — that's a
+      permanent stall. Call ``finish_scan`` (root) or ``agent_finish``
+      (subagent) instead. (In an interactive session there is always a user
+      who can message you, so parking to await the user is expected.)
     - If you're waiting on an agent that **isn't your child**, message
       it first asking it to ping you when done — otherwise it has no
       reason to send to your inbox and you'll wait the full timeout.

tests/test_execution.py

@@ -9,6 +9,7 @@ from typing import Any, cast
 from unittest.mock import MagicMock
 
 import pytest
+from agents.exceptions import MaxTurnsExceeded
 from agents.items import MessageOutputItem
 from agents.memory import SQLiteSession
 from agents.tool_context import ToolContext
@@ -785,3 +786,148 @@ async def test_run_agent_loop_seeds_identity_before_first_cycle(
     stored = await session.get_items()
     assert any("recon" in str(cast("dict[str, Any]", i).get("content", "")) for i in stored)
     session.close()
+
+
+def _scripted_cycle(
+    coordinator: AgentCoordinator,
+    agent_id: str,
+    statuses: list[str],
+    calls: list[Any],
+) -> Any:
+    """Fake run cycle that leaves ``agent_id`` in a scripted status per call."""
+
+    async def _cycle(*_args: Any, **kwargs: Any) -> Any:
+        calls.append(kwargs.get("input_data"))
+        status = statuses[min(len(calls) - 1, len(statuses) - 1)]
+        await coordinator.set_status(agent_id, status)
+        return MagicMock(final_output="plain text, no tool call")
+
+    return _cycle
+
+
+async def _drive(
+    coordinator: AgentCoordinator,
+    agent_id: str,
+    *,
+    interactive: bool,
+    max_turns: int = 5,
+) -> Any:
+    return await execution._run_until_lifecycle(
+        MagicMock(),
+        coordinator,
+        agent_id,
+        initial_input=[],
+        run_config=MagicMock(),
+        context={"agent_id": agent_id, "parent_id": None},
+        max_turns=max_turns,
+        session=None,
+        interactive=interactive,
+        event_sink=None,
+        hooks=None,
+    )
+
+
+@pytest.mark.asyncio
+async def test_interactive_text_only_turn_is_nudged_instead_of_parking(
+    monkeypatch: pytest.MonkeyPatch,
+) -> None:
+    """A no-tool-call turn must not silently hand control back to the user."""
+    coordinator = AgentCoordinator()
+    await coordinator.register("root", "strix", parent_id=None)
+    calls: list[Any] = []
+    monkeypatch.setattr(
+        execution,
+        "_run_cycle_parked",
+        _scripted_cycle(coordinator, "root", ["running", "completed"], calls),
+    )
+
+    await _drive(coordinator, "root", interactive=True)
+
+    assert len(calls) == 2
+    # The retry carries an explicit "call a tool" nudge rather than empty input.
+    nudge = calls[1][0]["content"]
+    assert "without a tool call" in nudge
+    assert "wait_for_message" in nudge
+    assert coordinator.statuses["root"] == "completed"
+
+
+@pytest.mark.asyncio
+async def test_interactive_wait_for_message_parks_without_a_nudge(
+    monkeypatch: pytest.MonkeyPatch,
+) -> None:
+    """``waiting`` is now only reachable by an explicit wait_for_message call."""
+    coordinator = AgentCoordinator()
+    await coordinator.register("root", "strix", parent_id=None)
+    calls: list[Any] = []
+    monkeypatch.setattr(
+        execution,
+        "_run_cycle_parked",
+        _scripted_cycle(coordinator, "root", ["waiting"], calls),
+    )
+
+    await _drive(coordinator, "root", interactive=True)
+
+    assert len(calls) == 1
+    assert coordinator.statuses["root"] == "waiting"
+
+
+@pytest.mark.asyncio
+async def test_interactive_recovery_exhaustion_parks_instead_of_crashing(
+    monkeypatch: pytest.MonkeyPatch,
+) -> None:
+    """A human can resume an interactive scan, so exhaustion parks rather than dies."""
+    coordinator = AgentCoordinator()
+    await coordinator.register("root", "strix", parent_id=None)
+    calls: list[Any] = []
+    monkeypatch.setattr(
+        execution,
+        "_run_cycle_parked",
+        _scripted_cycle(coordinator, "root", ["running"], calls),
+    )
+
+    await _drive(coordinator, "root", interactive=True)
+
+    assert len(calls) == execution._INTERACTIVE_TOOL_RECOVERY_LIMIT
+    assert coordinator.statuses["root"] == "waiting"
+
+
+@pytest.mark.asyncio
+async def test_noninteractive_recovery_exhaustion_crashes(
+    monkeypatch: pytest.MonkeyPatch,
+) -> None:
+    """No user is present to resume an autonomous run, so it still fails loudly."""
+    coordinator = AgentCoordinator()
+    await coordinator.register("root", "strix", parent_id=None)
+    calls: list[Any] = []
+    monkeypatch.setattr(
+        execution,
+        "_run_cycle",
+        _scripted_cycle(coordinator, "root", ["running"], calls),
+    )
+
+    with pytest.raises(MaxTurnsExceeded):
+        await _drive(coordinator, "root", interactive=False, max_turns=2)
+
+    assert len(calls) == 2
+    assert coordinator.statuses["root"] == "crashed"
+
+
+@pytest.mark.asyncio
+async def test_tool_required_message_is_persisted_to_the_session(tmp_path: Any) -> None:
+    session = SQLiteSession("root", tmp_path / "agents.db")
+
+    assert (
+        await execution._append_tool_required_message(
+            session=session,
+            context={"parent_id": None},
+            attempt=1,
+            limit=3,
+            interactive=True,
+        )
+        == []
+    )
+
+    stored = [cast("dict[str, Any]", i) for i in await session.get_items()]
+    assert "finish_scan" in stored[0]["content"]
+    assert "wait_for_message" in stored[0]["content"]
+    session.close()