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