style: revert unrelated Black-style formatting churn (#3220)

The earlier commits picked up a large amount of Black-style reformatting
(multi-line frozenset / keyword-arg wrapping / docstring blanks / removed
parens) on top of the actual guard fix. @chengyongru flagged it; the
first pass reverted some but not all.

This restores nanobot/providers/base.py, runner.py, heartbeat/service.py,
and utils/evaluator.py to origin/main and reapplies only the guard logic:

  - base.py: add should_execute_tools property
  - runner.py / heartbeat/service.py / utils/evaluator.py: route through it
    + log a warning when has_tool_calls but finish_reason is anomalous

Net diff vs main is now +87/-4 (was +211/-102) — roughly 30 lines of real
logic, which is what the PR is actually about.

Behavior unchanged from previous HEAD; full suite still 2014 passed.

Made-with: Cursor

nanobot/heartbeat/service.py

@@ -93,18 +93,12 @@ class HeartbeatService:
 
         response = await self.provider.chat_with_retry(
             messages=[
-                {
-                    "role": "system",
-                    "content": "You are a heartbeat agent. Call the heartbeat tool to report your decision.",
-                },
-                {
-                    "role": "user",
-                    "content": (
-                        f"Current Time: {current_time_str(self.timezone)}\n\n"
-                        "Review the following HEARTBEAT.md and decide whether there are active tasks.\n\n"
-                        f"{content}"
-                    ),
-                },
+                {"role": "system", "content": "You are a heartbeat agent. Call the heartbeat tool to report your decision."},
+                {"role": "user", "content": (
+                    f"Current Time: {current_time_str(self.timezone)}\n\n"
+                    "Review the following HEARTBEAT.md and decide whether there are active tasks.\n\n"
+                    f"{content}"
+                )},
             ],
             tools=_HEARTBEAT_TOOL,
             model=self.model,
@@ -113,7 +107,7 @@ class HeartbeatService:
         if not response.should_execute_tools:
             if response.has_tool_calls:
                 logger.warning(
-                    "Ignoring tool calls under finish_reason='%s' in heartbeat",
+                    "Ignoring heartbeat tool calls under finish_reason='{}'",
                     response.finish_reason,
                 )
             return "skip", ""
@@ -177,10 +171,7 @@ class HeartbeatService:
 
                 if response:
                     should_notify = await evaluate_response(
-                        response,
-                        tasks,
-                        self.provider,
-                        self.model,
+                        response, tasks, self.provider, self.model,
                     )
                     if should_notify and self.on_notify:
                         logger.info("Heartbeat: completed, delivering response")