fix: make subagent fail_on_tool_error configurable (#4198)

Add fail_on_tool_error to AgentDefaults and wire it through
AgentLoop -> SubagentManager -> AgentRunSpec.

Previously hardcoded to True in SubagentManager._run_subagent.
Now configurable via config.json with default True for backward
compatibility. When set to False, subagents can retry on minor
tool errors instead of immediately failing.

Changes:
- nanobot/config/schema.py: add fail_on_tool_error field (default True)
- nanobot/agent/subagent.py: accept and forward fail_on_tool_error
- nanobot/agent/loop.py: pass config through to SubagentManager
- tests/agent/test_subagent.py: add regression test

Signed-off-by: axelray-dev <110029405+axelray-dev@users.noreply.github.com>

nanobot/agent/loop.py

@@ -190,6 +190,7 @@ class AgentLoop:
         context_window_tokens: int | None = None,
         context_block_limit: int | None = None,
         max_tool_result_chars: int | None = None,
+        fail_on_tool_error: bool | None = None,
         provider_retry_mode: str = "standard",
         tool_hint_max_length: int | None = None,
         cron_service: CronService | None = None,
@@ -287,6 +288,7 @@ class AgentLoop:
             disabled_skills=disabled_skills,
             max_iterations=self.max_iterations,
             max_concurrent_subagents=max_concurrent_subagents,
+            fail_on_tool_error=fail_on_tool_error,
             llm_wall_timeout_for_session=lambda sk: runner_wall_llm_timeout_s(self.sessions, sk),
         )
         self._unified_session = unified_session
@@ -377,6 +379,7 @@ class AgentLoop:
             context_window_tokens=context_window_tokens,
             context_block_limit=defaults.context_block_limit,
             max_tool_result_chars=defaults.max_tool_result_chars,
+            fail_on_tool_error=defaults.fail_on_tool_error,
             provider_retry_mode=defaults.provider_retry_mode,
             tool_hint_max_length=defaults.tool_hint_max_length,
             restrict_to_workspace=config.tools.restrict_to_workspace,