fix: allow one retry for models that send interim text before tool calls

Some LLM providers (MiniMax, Gemini Flash, GPT-4.1, etc.) send an
initial text-only response like "Let me investigate..." before actually
making tool calls. The agent loop previously broke immediately on any
text response without tool calls, preventing these models from ever
using tools.

Now, when the model responds with text but hasn't used any tools yet,
the loop forwards the text as progress to the user and gives the model
one additional iteration to make tool calls. This is limited to a
single retry to prevent infinite loops.

Closes #705

nanobot/agent/loop.py

@@ -183,6 +183,7 @@ class AgentLoop:
         iteration = 0
         final_content = None
         tools_used: list[str] = []
+        text_only_retried = False
 
         while iteration < self.max_iterations:
             iteration += 1
@@ -226,6 +227,21 @@ class AgentLoop:
                     )
             else:
                 final_content = self._strip_think(response.content)
+                # Some models (MiniMax, Gemini Flash, GPT-4.1, etc.) send an
+                # interim text response (e.g. "Let me investigate...") before
+                # making tool calls. If no tools have been used yet and we
+                # haven't already retried, forward the text as progress and
+                # give the model one more chance to use tools.
+                if not tools_used and not text_only_retried and final_content:
+                    text_only_retried = True
+                    logger.debug(f"Interim text response (no tools used yet), retrying: {final_content[:80]}")
+                    if on_progress:
+                        await on_progress(final_content)
+                    messages = self.context.add_assistant_message(
+                        messages, response.content,
+                        reasoning_content=response.reasoning_content,
+                    )
+                    continue
                 break
 
         return final_content, tools_used