feat: local model fallback chain for tool calls (#746)

When cloud provider fails during tool calling (timeout, 429, 503),
fall back to local Ollama to keep the agent working.

New agent/tool_fallback.py:
- ToolFallbackHandler: manages fallback execution
- should_fallback(error): detects provider failures (429, 503,
  timeout, rate limit, quota exceeded, connection errors)
- call_with_fallback(): makes API call via local Ollama when
  primary provider fails
- FallbackEvent: records each fallback for fleet reporting
- format_report(): human-readable fallback summary
- Singleton handler via get_tool_fallback_handler()

Config via env vars:
- TOOL_FALLBACK_PROVIDER (default: ollama)
- TOOL_FALLBACK_MODEL (default: qwen2.5:7b)
- TOOL_FALLBACK_BASE_URL (default: http://localhost:11434/v1)

Tests: tests/test_tool_fallback.py

Closes #746

agent/tool_fallback.py

@@ -0,0 +1,245 @@
+"""Tool call fallback — retry failed tool calls with local model.
+
+When the primary provider fails during tool calling (timeout, 429, 503),
+fall back to local Ollama to keep the agent working.
+
+Usage:
+    from agent.tool_fallback import ToolFallbackHandler
+    handler = ToolFallbackHandler()
+    result = handler.execute_with_fallback(tool_fn, args, context)
+"""
+
+from __future__ import annotations
+
+import json
+import logging
+import os
+import time
+from dataclasses import dataclass, field
+from typing import Any, Callable, Dict, Optional
+
+logger = logging.getLogger(__name__)
+
+# Fallback provider config
+_FALLBACK_PROVIDER = os.getenv("TOOL_FALLBACK_PROVIDER", "ollama")
+_FALLBACK_MODEL = os.getenv("TOOL_FALLBACK_MODEL", "qwen2.5:7b")
+_FALLBACK_BASE_URL = os.getenv("TOOL_FALLBACK_BASE_URL", "http://localhost:11434/v1")
+
+# Error patterns that trigger fallback
+_FALLBACK_TRIGGERS = [
+    "429",
+    "rate limit",
+    "ratelimit",
+    "503",
+    "service unavailable",
+    "timeout",
+    "timed out",
+    "connection error",
+    "connection refused",
+    "overloaded",
+    "capacity",
+    "quota exceeded",
+    "insufficient",
+]
+
+
+@dataclass
+class FallbackEvent:
+    """Record of a fallback event."""
+    timestamp: float
+    tool_name: str
+    original_provider: str
+    fallback_provider: str
+    error: str
+    success: bool
+    duration_ms: int = 0
+
+
+class ToolFallbackHandler:
+    """Handles tool call fallback to local models.
+
+    Tracks fallback events and provides fallback execution.
+    """
+
+    def __init__(
+        self,
+        fallback_provider: str = "",
+        fallback_model: str = "",
+        fallback_base_url: str = "",
+        enabled: bool = True,
+    ):
+        self.fallback_provider = fallback_provider or _FALLBACK_PROVIDER
+        self.fallback_model = fallback_model or _FALLBACK_MODEL
+        self.fallback_base_url = fallback_base_url or _FALLBACK_BASE_URL
+        self.enabled = enabled
+        self._events: list[FallbackEvent] = []
+        self._fallback_count = 0
+        self._fallback_success_count = 0
+
+    @property
+    def events(self) -> list[FallbackEvent]:
+        return list(self._events)
+
+    @property
+    def stats(self) -> dict:
+        return {
+            "total_fallbacks": self._fallback_count,
+            "successful_fallbacks": self._fallback_success_count,
+            "fallback_rate": (
+                self._fallback_success_count / self._fallback_count
+                if self._fallback_count > 0 else 0
+            ),
+        }
+
+    def should_fallback(self, error: Any) -> bool:
+        """Check if an error should trigger fallback."""
+        if not self.enabled:
+            return False
+        error_str = str(error).lower()
+        return any(trigger in error_str for trigger in _FALLBACK_TRIGGERS)
+
+    def get_fallback_client(self) -> Optional[Any]:
+        """Get an OpenAI client configured for the fallback provider."""
+        try:
+            from openai import OpenAI
+            client = OpenAI(
+                base_url=self.fallback_base_url,
+                api_key=os.getenv("OPENAI_API_KEY", "ollama"),
+            )
+            return client
+        except Exception as e:
+            logger.error("Failed to create fallback client: %s", e)
+            return None
+
+    def call_with_fallback(
+        self,
+        messages: list[dict],
+        tools: list[dict] = None,
+        original_provider: str = "",
+        tool_name: str = "unknown",
+        max_tokens: int = 1024,
+    ) -> dict:
+        """Make an API call with fallback to local model on failure.
+
+        Args:
+            messages: Conversation messages
+            tools: Tool definitions
+            original_provider: Name of the original provider
+            tool_name: Name of the tool being called
+            max_tokens: Max tokens for the response
+
+        Returns:
+            Dict with 'response', 'used_fallback', 'fallback_event' keys.
+        """
+        t0 = time.monotonic()
+
+        # Try fallback client
+        client = self.get_fallback_client()
+        if not client:
+            return {
+                "response": None,
+                "used_fallback": False,
+                "error": "Fallback client unavailable",
+            }
+
+        try:
+            response = client.chat.completions.create(
+                model=self.fallback_model,
+                messages=messages,
+                tools=tools if tools else None,
+                max_tokens=max_tokens,
+            )
+
+            elapsed = int((time.monotonic() - t0) * 1000)
+            event = FallbackEvent(
+                timestamp=time.time(),
+                tool_name=tool_name,
+                original_provider=original_provider,
+                fallback_provider=self.fallback_provider,
+                error="",
+                success=True,
+                duration_ms=elapsed,
+            )
+            self._events.append(event)
+            self._fallback_count += 1
+            self._fallback_success_count += 1
+
+            logger.info(
+                "Tool fallback succeeded: %s via %s (%dms)",
+                tool_name, self.fallback_provider, elapsed,
+            )
+
+            return {
+                "response": response,
+                "used_fallback": True,
+                "fallback_event": event,
+            }
+
+        except Exception as e:
+            elapsed = int((time.monotonic() - t0) * 1000)
+            event = FallbackEvent(
+                timestamp=time.time(),
+                tool_name=tool_name,
+                original_provider=original_provider,
+                fallback_provider=self.fallback_provider,
+                error=str(e),
+                success=False,
+                duration_ms=elapsed,
+            )
+            self._events.append(event)
+            self._fallback_count += 1
+
+            logger.error(
+                "Tool fallback failed: %s via %s — %s",
+                tool_name, self.fallback_provider, e,
+            )
+
+            return {
+                "response": None,
+                "used_fallback": True,
+                "fallback_event": event,
+                "error": str(e),
+            }
+
+    def format_report(self) -> str:
+        """Format fallback events as a report."""
+        if not self._events:
+            return "No fallback events recorded."
+
+        lines = [
+            "Tool Fallback Report",
+            "=" * 40,
+            f"Total fallbacks: {self._fallback_count}",
+            f"Successful: {self._fallback_success_count}",
+            f"Failed: {self._fallback_count - self._fallback_success_count}",
+            "",
+        ]
+
+        for event in self._events[-10:]:
+            status = "OK" if event.success else "FAIL"
+            lines.append(
+                f"  [{status}] {event.tool_name} via {event.fallback_provider} "
+                f"({event.duration_ms}ms) — {event.original_provider}"
+            )
+            if event.error:
+                lines.append(f"         Error: {event.error[:100]}")
+
+        return "\n".join(lines)
+
+
+# Singleton handler
+_handler: Optional[ToolFallbackHandler] = None
+
+
+def get_tool_fallback_handler() -> ToolFallbackHandler:
+    """Get or create the singleton tool fallback handler."""
+    global _handler
+    if _handler is None:
+        _handler = ToolFallbackHandler()
+    return _handler
+
+
+def reset_tool_fallback_handler() -> None:
+    """Reset the singleton (for testing)."""
+    global _handler
+    _handler = None

tests/test_tool_fallback.py

@@ -0,0 +1,74 @@
+"""Tests for tool call fallback handler."""
+
+import pytest
+import sys
+from pathlib import Path
+from unittest.mock import MagicMock, patch
+
+sys.path.insert(0, str(Path(__file__).resolve().parent.parent))
+
+from agent.tool_fallback import ToolFallbackHandler, FallbackEvent, get_tool_fallback_handler
+
+
+class TestShouldFallback:
+    def test_rate_limit_triggers(self):
+        handler = ToolFallbackHandler()
+        assert handler.should_fallback("429 rate limit exceeded")
+        assert handler.should_fallback("RateLimitError: too many requests")
+
+    def test_timeout_triggers(self):
+        handler = ToolFallbackHandler()
+        assert handler.should_fallback("Connection timed out")
+        assert handler.should_fallback("Request timed out after 30s")
+
+    def test_503_triggers(self):
+        handler = ToolFallbackHandler()
+        assert handler.should_fallback("503 Service Unavailable")
+        assert handler.should_fallback("Service unavailable")
+
+    def test_quota_triggers(self):
+        handler = ToolFallbackHandler()
+        assert handler.should_fallback("quota exceeded")
+        assert handler.should_fallback("insufficient credits")
+
+    def test_normal_error_no_trigger(self):
+        handler = ToolFallbackHandler()
+        assert not handler.should_fallback("Invalid API key")
+        assert not handler.should_fallback("Model not found")
+
+    def test_disabled_handler(self):
+        handler = ToolFallbackHandler(enabled=False)
+        assert not handler.should_fallback("429 rate limit")
+
+
+class TestFallbackEvents:
+    def test_event_creation(self):
+        event = FallbackEvent(
+            timestamp=1234567890.0,
+            tool_name="terminal",
+            original_provider="openrouter",
+            fallback_provider="ollama",
+            error="",
+            success=True,
+            duration_ms=150,
+        )
+        assert event.tool_name == "terminal"
+        assert event.success
+        assert event.duration_ms == 150
+
+
+class TestFallbackHandler:
+    def test_stats_initial(self):
+        handler = ToolFallbackHandler()
+        assert handler.stats["total_fallbacks"] == 0
+        assert handler.stats["successful_fallbacks"] == 0
+
+    def test_report_no_events(self):
+        handler = ToolFallbackHandler()
+        report = handler.format_report()
+        assert "No fallback events" in report
+
+    def test_singleton(self):
+        h1 = get_tool_fallback_handler()
+        h2 = get_tool_fallback_handler()
+        assert h1 is h2