feat: Anthropic API budget checker, fails open on error

bin/check_budget.py

@@ -0,0 +1,36 @@
+"""Check Anthropic API budget usage. Fails open (returns True) on errors."""
+import os
+import sys
+import urllib.request
+import urllib.error
+import json
+
+USAGE_API = "https://api.anthropic.com/v1/usage"
+
+def get_used_usd() -> float:
+    api_key = os.environ.get('ANTHROPIC_API_KEY', '')
+    if not api_key:
+        raise EnvironmentError("ANTHROPIC_API_KEY not set")
+    req = urllib.request.Request(
+        USAGE_API,
+        headers={
+            "x-api-key": api_key,
+            "anthropic-version": "2023-06-01",
+        }
+    )
+    with urllib.request.urlopen(req, timeout=5) as resp:
+        data = json.loads(resp.read())
+    return sum(item.get('cost_usd', 0.0) for item in data.get('data', []))
+
+def is_budget_ok(limit_usd: float) -> bool:
+    try:
+        used = get_used_usd()
+        return used < limit_usd
+    except Exception:
+        return True  # fail open
+
+if __name__ == '__main__':
+    limit = float(sys.argv[1]) if len(sys.argv) > 1 else 5.0
+    ok = is_budget_ok(limit)
+    print("ok" if ok else "low")
+    sys.exit(0 if ok else 1)

tests/test_check_budget.py

@@ -0,0 +1,22 @@
+import sys
+sys.path.insert(0, 'bin')
+from unittest.mock import patch
+import pytest
+from check_budget import is_budget_ok, get_used_usd
+
+def test_budget_ok_when_used_less_than_limit():
+    with patch('check_budget.get_used_usd', return_value=2.0):
+        assert is_budget_ok(limit_usd=5.0) is True
+
+def test_budget_not_ok_when_used_exceeds_limit():
+    with patch('check_budget.get_used_usd', return_value=5.5):
+        assert is_budget_ok(limit_usd=5.0) is False
+
+def test_budget_ok_on_api_error():
+    """Fail open: if we can't check the budget, assume OK to avoid blocking research."""
+    with patch('check_budget.get_used_usd', side_effect=Exception("network error")):
+        assert is_budget_ok(limit_usd=5.0) is True
+
+def test_budget_exactly_at_limit_is_not_ok():
+    with patch('check_budget.get_used_usd', return_value=5.0):
+        assert is_budget_ok(limit_usd=5.0) is False