Budget guard: ratio 2.07 measured, limit 142; limit read from .env at each check

Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>

harness/ledger.py

@@ -34,9 +34,24 @@ def spent(since=None):
     return round(sum(json.loads(l)["usd"] for l in open(LEDGER) if json.loads(l)["day"] >= since), 4)
 
 
+def _env_budget():
+    """BUDGET_LIMIT_USD and BUDGET_RESERVE_USD from .env (read at each check: a change applies at once)."""
+    vals = {"BUDGET_LIMIT_USD": os.environ.get("BUDGET_LIMIT_USD", "45"),
+            "BUDGET_RESERVE_USD": os.environ.get("BUDGET_RESERVE_USD", "0")}
+    try:
+        for line in open(os.path.join(ROOT, ".env")):
+            k, _, v = line.strip().partition("=")
+            if k in vals and v:
+                vals[k] = v
+    except OSError:
+        pass
+    return float(vals["BUDGET_LIMIT_USD"]), float(vals["BUDGET_RESERVE_USD"])
+
+
 def check_budget():
     # BUDGET_RESERVE_USD: ledger USD kept back (second teacher test later); the guard stops at limit - reserve
-    limit = float(os.environ.get("BUDGET_LIMIT_USD", "45")) - float(os.environ.get("BUDGET_RESERVE_USD", "0"))
+    limit_raw, reserve = _env_budget()
+    limit = limit_raw - reserve
     s = spent()
     if s >= limit:
         raise BudgetExceeded(f"cycle spend {s} USD >= limit {limit} USD")