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,

nanobot/agent/subagent.py

@@ -86,6 +86,7 @@ class SubagentManager:
         disabled_skills: list[str] | None = None,
         max_iterations: int | None = None,
         max_concurrent_subagents: int | None = None,
+        fail_on_tool_error: bool | None = None,
         llm_wall_timeout_for_session: Callable[[str | None], float | None] | None = None,
     ):
         defaults = AgentDefaults()
@@ -107,6 +108,11 @@ class SubagentManager:
             if max_concurrent_subagents is not None
             else defaults.max_concurrent_subagents
         )
+        self.fail_on_tool_error = (
+            fail_on_tool_error
+            if fail_on_tool_error is not None
+            else defaults.fail_on_tool_error
+        )
         self.runner = AgentRunner(provider)
         self._llm_wall_timeout_for_session = llm_wall_timeout_for_session
         self._running_tasks: dict[str, asyncio.Task[None]] = {}
@@ -251,7 +257,7 @@ class SubagentManager:
                     max_iterations_message="Task completed but no final response was generated.",
                     finalize_on_max_iterations=False,
                     error_message=None,
-                    fail_on_tool_error=True,
+                    fail_on_tool_error=self.fail_on_tool_error,
                     checkpoint_callback=_on_checkpoint,
                     session_key=sess_key,
                     workspace=root,

nanobot/config/schema.py

@@ -132,6 +132,7 @@ class AgentDefaults(Base):
     fallback_models: list[FallbackCandidate] = Field(default_factory=list)
     max_tool_iterations: int = 200
     max_concurrent_subagents: int = Field(default=1, ge=1)
+    fail_on_tool_error: bool = True
     max_tool_result_chars: int = 16_000
     provider_retry_mode: Literal["standard", "persistent"] = "standard"
     tool_hint_max_length: int = Field(