diff --git a/tests/infrastructure/test_models_budget.py b/tests/infrastructure/test_models_budget.py
new file mode 100644
index 00000000..017933c5
--- /dev/null
+++ b/tests/infrastructure/test_models_budget.py
@@ -0,0 +1,598 @@
+"""Unit tests for models/budget.py — comprehensive coverage for budget management.
+
+Tests budget allocation, tracking, limit enforcement, and edge cases including:
+- Zero budget scenarios
+- Over-budget handling
+- Budget reset behavior
+- In-memory fallback when DB is unavailable
+"""
+
+import threading
+import time
+from datetime import UTC, date, datetime, timedelta
+from unittest.mock import patch
+
+import pytest
+
+from infrastructure.models.budget import (
+    BudgetTracker,
+    SpendRecord,
+    estimate_cost_usd,
+    get_budget_tracker,
+)
+
+pytestmark = pytest.mark.unit
+
+
+# ── Test SpendRecord dataclass ────────────────────────────────────────────────
+
+
+class TestSpendRecord:
+    """Tests for the SpendRecord dataclass."""
+
+    def test_spend_record_creation(self):
+        """Test creating a SpendRecord with all fields."""
+        ts = time.time()
+        record = SpendRecord(
+            ts=ts,
+            provider="anthropic",
+            model="claude-haiku-4-5",
+            tokens_in=100,
+            tokens_out=200,
+            cost_usd=0.001,
+            tier="cloud",
+        )
+        assert record.ts == ts
+        assert record.provider == "anthropic"
+        assert record.model == "claude-haiku-4-5"
+        assert record.tokens_in == 100
+        assert record.tokens_out == 200
+        assert record.cost_usd == 0.001
+        assert record.tier == "cloud"
+
+    def test_spend_record_with_zero_tokens(self):
+        """Test SpendRecord with zero tokens."""
+        ts = time.time()
+        record = SpendRecord(ts=ts, provider="openai", model="gpt-4o", tokens_in=0, tokens_out=0, cost_usd=0.0, tier="cloud")
+        assert record.tokens_in == 0
+        assert record.tokens_out == 0
+
+
+# ── Test estimate_cost_usd function ───────────────────────────────────────────
+
+
+class TestEstimateCostUsd:
+    """Tests for the estimate_cost_usd function."""
+
+    def test_haiku_cheaper_than_sonnet(self):
+        """Haiku should be cheaper than Sonnet for same tokens."""
+        haiku_cost = estimate_cost_usd("claude-haiku-4-5", 1000, 1000)
+        sonnet_cost = estimate_cost_usd("claude-sonnet-4-5", 1000, 1000)
+        assert haiku_cost < sonnet_cost
+
+    def test_zero_tokens_is_zero_cost(self):
+        """Zero tokens should result in zero cost."""
+        assert estimate_cost_usd("gpt-4o", 0, 0) == 0.0
+
+    def test_only_input_tokens(self):
+        """Cost calculation with only input tokens."""
+        cost = estimate_cost_usd("gpt-4o", 1000, 0)
+        expected = (1000 * 0.0025) / 1000.0  # $0.0025 per 1K input tokens
+        assert cost == pytest.approx(expected)
+
+    def test_only_output_tokens(self):
+        """Cost calculation with only output tokens."""
+        cost = estimate_cost_usd("gpt-4o", 0, 1000)
+        expected = (1000 * 0.01) / 1000.0  # $0.01 per 1K output tokens
+        assert cost == pytest.approx(expected)
+
+    def test_unknown_model_uses_default(self):
+        """Unknown model should use conservative default cost."""
+        cost = estimate_cost_usd("some-unknown-model-xyz", 1000, 1000)
+        assert cost > 0  # Uses conservative default, not zero
+        # Default is 0.003 input, 0.015 output per 1K
+        expected = (1000 * 0.003 + 1000 * 0.015) / 1000.0
+        assert cost == pytest.approx(expected)
+
+    def test_versioned_model_name_matches(self):
+        """Versioned model names should match base model rates."""
+        cost1 = estimate_cost_usd("claude-haiku-4-5-20251001", 1000, 0)
+        cost2 = estimate_cost_usd("claude-haiku-4-5", 1000, 0)
+        assert cost1 == cost2
+
+    def test_gpt4o_mini_cheaper_than_gpt4o(self):
+        """GPT-4o mini should be cheaper than GPT-4o."""
+        mini = estimate_cost_usd("gpt-4o-mini", 1000, 1000)
+        full = estimate_cost_usd("gpt-4o", 1000, 1000)
+        assert mini < full
+
+    def test_opus_most_expensive_claude(self):
+        """Opus should be the most expensive Claude model."""
+        opus = estimate_cost_usd("claude-opus-4-5", 1000, 1000)
+        sonnet = estimate_cost_usd("claude-sonnet-4-5", 1000, 1000)
+        haiku = estimate_cost_usd("claude-haiku-4-5", 1000, 1000)
+        assert opus > sonnet > haiku
+
+    def test_grok_variants(self):
+        """Test Grok model cost estimation."""
+        cost = estimate_cost_usd("grok-3", 1000, 1000)
+        assert cost > 0
+        cost_fast = estimate_cost_usd("grok-3-fast", 1000, 1000)
+        assert cost_fast > 0
+
+    def test_case_insensitive_matching(self):
+        """Model name matching should be case insensitive."""
+        cost_lower = estimate_cost_usd("claude-haiku-4-5", 1000, 0)
+        cost_upper = estimate_cost_usd("CLAUDE-HAIKU-4-5", 1000, 0)
+        cost_mixed = estimate_cost_usd("Claude-Haiku-4-5", 1000, 0)
+        assert cost_lower == cost_upper == cost_mixed
+
+    def test_returns_float(self):
+        """Function should always return a float."""
+        assert isinstance(estimate_cost_usd("haiku", 100, 200), float)
+        assert isinstance(estimate_cost_usd("unknown-model", 100, 200), float)
+        assert isinstance(estimate_cost_usd("haiku", 0, 0), float)
+
+
+# ── Test BudgetTracker initialization ─────────────────────────────────────────
+
+
+class TestBudgetTrackerInit:
+    """Tests for BudgetTracker initialization."""
+
+    def test_creates_with_memory_db(self):
+        """Tracker should initialize with in-memory database."""
+        tracker = BudgetTracker(db_path=":memory:")
+        assert tracker._db_ok is True
+
+    def test_in_memory_fallback_empty_on_creation(self):
+        """In-memory fallback should start empty."""
+        tracker = BudgetTracker(db_path=":memory:")
+        assert tracker._in_memory == []
+
+    def test_custom_db_path(self, tmp_path):
+        """Tracker should use custom database path."""
+        db_file = tmp_path / "custom_budget.db"
+        tracker = BudgetTracker(db_path=str(db_file))
+        assert tracker._db_ok is True
+        assert tracker._db_path == str(db_file)
+        assert db_file.exists()
+
+    def test_db_path_directory_creation(self, tmp_path):
+        """Tracker should create parent directories if needed."""
+        db_file = tmp_path / "nested" / "dirs" / "budget.db"
+        tracker = BudgetTracker(db_path=str(db_file))
+        assert tracker._db_ok is True
+        assert db_file.parent.exists()
+
+    def test_invalid_db_path_fallback(self):
+        """Tracker should fallback to in-memory on invalid path."""
+        # Use a path that cannot be created (e.g., permission denied simulation)
+        tracker = BudgetTracker.__new__(BudgetTracker)
+        tracker._db_path = "/nonexistent/invalid/path/budget.db"
+        tracker._lock = threading.Lock()
+        tracker._in_memory = []
+        tracker._db_ok = False
+        # Should still work with in-memory fallback
+        cost = tracker.record_spend("test", "model", cost_usd=0.01)
+        assert cost == 0.01
+
+
+# ── Test BudgetTracker record_spend ───────────────────────────────────────────
+
+
+class TestBudgetTrackerRecordSpend:
+    """Tests for recording spend events."""
+
+    def test_record_spend_returns_cost(self):
+        """record_spend should return the calculated cost."""
+        tracker = BudgetTracker(db_path=":memory:")
+        cost = tracker.record_spend("anthropic", "claude-haiku-4-5", 100, 200)
+        assert cost > 0
+
+    def test_record_spend_explicit_cost(self):
+        """record_spend should use explicit cost when provided."""
+        tracker = BudgetTracker(db_path=":memory:")
+        cost = tracker.record_spend("anthropic", "model", cost_usd=1.23)
+        assert cost == pytest.approx(1.23)
+
+    def test_record_spend_accumulates(self):
+        """Multiple spend records should accumulate correctly."""
+        tracker = BudgetTracker(db_path=":memory:")
+        tracker.record_spend("openai", "gpt-4o", cost_usd=0.01)
+        tracker.record_spend("openai", "gpt-4o", cost_usd=0.02)
+        assert tracker.get_daily_spend() == pytest.approx(0.03, abs=1e-9)
+
+    def test_record_spend_with_tier_label(self):
+        """record_spend should accept custom tier labels."""
+        tracker = BudgetTracker(db_path=":memory:")
+        cost = tracker.record_spend("anthropic", "haiku", tier="cloud_api")
+        assert cost >= 0
+
+    def test_record_spend_with_provider(self):
+        """record_spend should track provider correctly."""
+        tracker = BudgetTracker(db_path=":memory:")
+        tracker.record_spend("openai", "gpt-4o", cost_usd=0.01)
+        tracker.record_spend("anthropic", "claude-haiku", cost_usd=0.02)
+        assert tracker.get_daily_spend() == pytest.approx(0.03, abs=1e-9)
+
+    def test_record_zero_cost(self):
+        """Recording zero cost should work correctly."""
+        tracker = BudgetTracker(db_path=":memory:")
+        cost = tracker.record_spend("test", "model", cost_usd=0.0)
+        assert cost == 0.0
+        assert tracker.get_daily_spend() == 0.0
+
+    def test_record_negative_cost(self):
+        """Recording negative cost (refund) should work."""
+        tracker = BudgetTracker(db_path=":memory:")
+        cost = tracker.record_spend("test", "model", cost_usd=-0.50)
+        assert cost == -0.50
+        assert tracker.get_daily_spend() == -0.50
+
+
+# ── Test BudgetTracker daily/monthly spend queries ────────────────────────────
+
+
+class TestBudgetTrackerSpendQueries:
+    """Tests for daily and monthly spend queries."""
+
+    def test_monthly_spend_includes_daily(self):
+        """Monthly spend should be >= daily spend."""
+        tracker = BudgetTracker(db_path=":memory:")
+        tracker.record_spend("anthropic", "haiku", cost_usd=5.00)
+        assert tracker.get_monthly_spend() >= tracker.get_daily_spend()
+
+    def test_get_daily_spend_empty(self):
+        """Daily spend should be zero when no records."""
+        tracker = BudgetTracker(db_path=":memory:")
+        assert tracker.get_daily_spend() == 0.0
+
+    def test_get_monthly_spend_empty(self):
+        """Monthly spend should be zero when no records."""
+        tracker = BudgetTracker(db_path=":memory:")
+        assert tracker.get_monthly_spend() == 0.0
+
+    def test_daily_spend_isolation(self):
+        """Daily spend should only include today's records, not old ones."""
+        tracker = BudgetTracker(db_path=":memory:")
+        # Force use of in-memory fallback
+        tracker._db_ok = False
+
+        # Add record for today
+        today_ts = datetime.combine(date.today(), datetime.min.time(), tzinfo=UTC).timestamp()
+        tracker._in_memory.append(
+            SpendRecord(today_ts + 3600, "test", "model", 0, 0, 1.0, "cloud")
+        )
+
+        # Add old record (2 days ago)
+        old_ts = (datetime.now(UTC) - timedelta(days=2)).timestamp()
+        tracker._in_memory.append(
+            SpendRecord(old_ts, "test", "old_model", 0, 0, 2.0, "cloud")
+        )
+
+        # Daily should only include today's 1.0
+        assert tracker.get_daily_spend() == pytest.approx(1.0, abs=1e-9)
+        # Monthly should include both (both are in current month)
+        assert tracker.get_monthly_spend() == pytest.approx(3.0, abs=1e-9)
+
+
+# ── Test BudgetTracker cloud_allowed ──────────────────────────────────────────
+
+
+class TestBudgetTrackerCloudAllowed:
+    """Tests for cloud budget limit enforcement."""
+
+    def test_allowed_when_no_spend(self):
+        """Cloud should be allowed when no spend recorded."""
+        tracker = BudgetTracker(db_path=":memory:")
+        assert tracker.cloud_allowed() is True
+
+    def test_blocked_when_daily_limit_exceeded(self):
+        """Cloud should be blocked when daily limit exceeded."""
+        tracker = BudgetTracker(db_path=":memory:")
+        tracker.record_spend("anthropic", "haiku", cost_usd=999.0)
+        # With default daily limit of 5.0, 999 should block
+        assert tracker.cloud_allowed() is False
+
+    def test_allowed_when_daily_limit_zero(self):
+        """Cloud should be allowed when daily limit is 0 (disabled)."""
+        tracker = BudgetTracker(db_path=":memory:")
+        tracker.record_spend("anthropic", "haiku", cost_usd=999.0)
+        with patch("infrastructure.models.budget.settings") as mock_settings:
+            mock_settings.tier_cloud_daily_budget_usd = 0  # disabled
+            mock_settings.tier_cloud_monthly_budget_usd = 0  # disabled
+            assert tracker.cloud_allowed() is True
+
+    def test_blocked_when_monthly_limit_exceeded(self):
+        """Cloud should be blocked when monthly limit exceeded."""
+        tracker = BudgetTracker(db_path=":memory:")
+        tracker.record_spend("anthropic", "haiku", cost_usd=999.0)
+        with patch("infrastructure.models.budget.settings") as mock_settings:
+            mock_settings.tier_cloud_daily_budget_usd = 0  # daily disabled
+            mock_settings.tier_cloud_monthly_budget_usd = 10.0
+            assert tracker.cloud_allowed() is False
+
+    def test_allowed_at_exact_daily_limit(self):
+        """Cloud should be allowed when exactly at daily limit."""
+        tracker = BudgetTracker(db_path=":memory:")
+        with patch("infrastructure.models.budget.settings") as mock_settings:
+            mock_settings.tier_cloud_daily_budget_usd = 5.0
+            mock_settings.tier_cloud_monthly_budget_usd = 0
+            # Record exactly at limit
+            tracker.record_spend("test", "model", cost_usd=5.0)
+            # At exactly the limit, it should return False (blocked)
+            # because spend >= limit
+            assert tracker.cloud_allowed() is False
+
+    def test_allowed_below_daily_limit(self):
+        """Cloud should be allowed when below daily limit."""
+        tracker = BudgetTracker(db_path=":memory:")
+        with patch("infrastructure.models.budget.settings") as mock_settings:
+            mock_settings.tier_cloud_daily_budget_usd = 5.0
+            mock_settings.tier_cloud_monthly_budget_usd = 0
+            tracker.record_spend("test", "model", cost_usd=4.99)
+            assert tracker.cloud_allowed() is True
+
+    def test_zero_budget_blocks_all(self):
+        """Zero budget should block all cloud usage."""
+        tracker = BudgetTracker(db_path=":memory:")
+        with patch("infrastructure.models.budget.settings") as mock_settings:
+            mock_settings.tier_cloud_daily_budget_usd = 0.01  # Very small budget
+            mock_settings.tier_cloud_monthly_budget_usd = 0
+            tracker.record_spend("test", "model", cost_usd=0.02)
+            # Over the tiny budget, should be blocked
+            assert tracker.cloud_allowed() is False
+
+    def test_both_limits_checked(self):
+        """Both daily and monthly limits should be checked."""
+        tracker = BudgetTracker(db_path=":memory:")
+        with patch("infrastructure.models.budget.settings") as mock_settings:
+            mock_settings.tier_cloud_daily_budget_usd = 100.0
+            mock_settings.tier_cloud_monthly_budget_usd = 10.0
+            tracker.record_spend("test", "model", cost_usd=15.0)
+            # Under daily but over monthly
+            assert tracker.cloud_allowed() is False
+
+
+# ── Test BudgetTracker summary ────────────────────────────────────────────────
+
+
+class TestBudgetTrackerSummary:
+    """Tests for budget summary functionality."""
+
+    def test_summary_keys_present(self):
+        """Summary should contain all expected keys."""
+        tracker = BudgetTracker(db_path=":memory:")
+        summary = tracker.get_summary()
+        assert "daily_usd" in summary
+        assert "monthly_usd" in summary
+        assert "daily_limit_usd" in summary
+        assert "monthly_limit_usd" in summary
+        assert "daily_ok" in summary
+        assert "monthly_ok" in summary
+
+    def test_summary_daily_ok_true_on_empty(self):
+        """daily_ok and monthly_ok should be True when empty."""
+        tracker = BudgetTracker(db_path=":memory:")
+        summary = tracker.get_summary()
+        assert summary["daily_ok"] is True
+        assert summary["monthly_ok"] is True
+
+    def test_summary_daily_ok_false_when_exceeded(self):
+        """daily_ok should be False when daily limit exceeded."""
+        tracker = BudgetTracker(db_path=":memory:")
+        tracker.record_spend("openai", "gpt-4o", cost_usd=999.0)
+        summary = tracker.get_summary()
+        assert summary["daily_ok"] is False
+
+    def test_summary_monthly_ok_false_when_exceeded(self):
+        """monthly_ok should be False when monthly limit exceeded."""
+        tracker = BudgetTracker(db_path=":memory:")
+        with patch("infrastructure.models.budget.settings") as mock_settings:
+            mock_settings.tier_cloud_daily_budget_usd = 0
+            mock_settings.tier_cloud_monthly_budget_usd = 10.0
+            tracker.record_spend("openai", "gpt-4o", cost_usd=15.0)
+            summary = tracker.get_summary()
+            assert summary["monthly_ok"] is False
+
+    def test_summary_values_rounded(self):
+        """Summary values should be rounded appropriately."""
+        tracker = BudgetTracker(db_path=":memory:")
+        tracker.record_spend("test", "model", cost_usd=1.123456789)
+        summary = tracker.get_summary()
+        # daily_usd should be rounded to 6 decimal places
+        assert summary["daily_usd"] == 1.123457
+
+    def test_summary_with_disabled_limits(self):
+        """Summary should handle disabled limits (0)."""
+        tracker = BudgetTracker(db_path=":memory:")
+        with patch("infrastructure.models.budget.settings") as mock_settings:
+            mock_settings.tier_cloud_daily_budget_usd = 0
+            mock_settings.tier_cloud_monthly_budget_usd = 0
+            tracker.record_spend("test", "model", cost_usd=100.0)
+            summary = tracker.get_summary()
+            assert summary["daily_limit_usd"] == 0
+            assert summary["monthly_limit_usd"] == 0
+            assert summary["daily_ok"] is True
+            assert summary["monthly_ok"] is True
+
+
+# ── Test BudgetTracker in-memory fallback ─────────────────────────────────────
+
+
+class TestBudgetTrackerInMemoryFallback:
+    """Tests for in-memory fallback when DB is unavailable."""
+
+    def test_in_memory_records_persisted(self):
+        """Records should be stored in memory when DB is unavailable."""
+        tracker = BudgetTracker(db_path=":memory:")
+        # Force DB to appear unavailable
+        tracker._db_ok = False
+        tracker.record_spend("test", "model", cost_usd=0.01)
+        assert len(tracker._in_memory) == 1
+        assert tracker._in_memory[0].cost_usd == 0.01
+
+    def test_in_memory_query_spend(self):
+        """Query spend should work with in-memory fallback."""
+        tracker = BudgetTracker(db_path=":memory:")
+        tracker._db_ok = False
+        tracker.record_spend("test", "model", cost_usd=0.01)
+        # Query should work from in-memory
+        since_ts = (datetime.now(UTC) - timedelta(hours=1)).timestamp()
+        result = tracker._query_spend(since_ts)
+        assert result == 0.01
+
+    def test_in_memory_older_records_not_counted(self):
+        """In-memory records older than since_ts should not be counted."""
+        tracker = BudgetTracker(db_path=":memory:")
+        tracker._db_ok = False
+        old_ts = (datetime.now(UTC) - timedelta(days=2)).timestamp()
+        tracker._in_memory.append(
+            SpendRecord(old_ts, "test", "model", 0, 0, 1.0, "cloud")
+        )
+        # Query for records in last day
+        since_ts = (datetime.now(UTC) - timedelta(days=1)).timestamp()
+        result = tracker._query_spend(since_ts)
+        assert result == 0.0
+
+
+# ── Test BudgetTracker thread safety ──────────────────────────────────────────
+
+
+class TestBudgetTrackerThreadSafety:
+    """Tests for thread-safe operations."""
+
+    def test_concurrent_record_spend(self):
+        """Multiple threads should safely record spend concurrently."""
+        tracker = BudgetTracker(db_path=":memory:")
+        results = []
+        errors = []
+
+        def record_spends():
+            try:
+                for _ in range(10):
+                    cost = tracker.record_spend("test", "model", cost_usd=0.01)
+                    results.append(cost)
+            except Exception as e:
+                errors.append(e)
+
+        threads = [threading.Thread(target=record_spends) for _ in range(5)]
+        for t in threads:
+            t.start()
+        for t in threads:
+            t.join()
+
+        assert len(errors) == 0
+        assert len(results) == 50
+        assert tracker.get_daily_spend() == pytest.approx(0.50, abs=1e-9)
+
+
+# ── Test BudgetTracker edge cases ─────────────────────────────────────────────
+
+
+class TestBudgetTrackerEdgeCases:
+    """Tests for edge cases and boundary conditions."""
+
+    def test_very_small_cost(self):
+        """Tracker should handle very small costs."""
+        tracker = BudgetTracker(db_path=":memory:")
+        tracker.record_spend("test", "model", cost_usd=0.000001)
+        assert tracker.get_daily_spend() == pytest.approx(0.000001, abs=1e-9)
+
+    def test_very_large_cost(self):
+        """Tracker should handle very large costs."""
+        tracker = BudgetTracker(db_path=":memory:")
+        tracker.record_spend("test", "model", cost_usd=1_000_000.0)
+        assert tracker.get_daily_spend() == pytest.approx(1_000_000.0, abs=1e-9)
+
+    def test_many_records(self):
+        """Tracker should handle many records efficiently."""
+        tracker = BudgetTracker(db_path=":memory:")
+        for i in range(100):
+            tracker.record_spend(f"provider_{i}", f"model_{i}", cost_usd=0.01)
+        assert tracker.get_daily_spend() == pytest.approx(1.0, abs=1e-9)
+
+    def test_empty_provider_name(self):
+        """Tracker should handle empty provider name."""
+        tracker = BudgetTracker(db_path=":memory:")
+        cost = tracker.record_spend("", "model", cost_usd=0.01)
+        assert cost == 0.01
+
+    def test_empty_model_name(self):
+        """Tracker should handle empty model name."""
+        tracker = BudgetTracker(db_path=":memory:")
+        cost = tracker.record_spend("provider", "", cost_usd=0.01)
+        assert cost == 0.01
+
+
+# ── Test get_budget_tracker singleton ─────────────────────────────────────────
+
+
+class TestGetBudgetTrackerSingleton:
+    """Tests for the module-level BudgetTracker singleton."""
+
+    def test_returns_budget_tracker(self):
+        """Singleton should return a BudgetTracker instance."""
+        import infrastructure.models.budget as bmod
+
+        bmod._budget_tracker = None
+        tracker = get_budget_tracker()
+        assert isinstance(tracker, BudgetTracker)
+
+    def test_returns_same_instance(self):
+        """Singleton should return the same instance."""
+        import infrastructure.models.budget as bmod
+
+        bmod._budget_tracker = None
+        t1 = get_budget_tracker()
+        t2 = get_budget_tracker()
+        assert t1 is t2
+
+    def test_singleton_persists_state(self):
+        """Singleton should persist state across calls."""
+        import infrastructure.models.budget as bmod
+
+        bmod._budget_tracker = None
+        tracker1 = get_budget_tracker()
+        # Record spend
+        tracker1.record_spend("test", "model", cost_usd=1.0)
+        # Get singleton again
+        tracker2 = get_budget_tracker()
+        assert tracker1 is tracker2
+
+
+# ── Test BudgetTracker with mocked settings ───────────────────────────────────
+
+
+class TestBudgetTrackerWithMockedSettings:
+    """Tests using mocked settings for different scenarios."""
+
+    def test_high_daily_limit(self):
+        """Test with high daily limit."""
+        tracker = BudgetTracker(db_path=":memory:")
+        with patch("infrastructure.models.budget.settings") as mock_settings:
+            mock_settings.tier_cloud_daily_budget_usd = 1000.0
+            mock_settings.tier_cloud_monthly_budget_usd = 10000.0
+            tracker.record_spend("test", "model", cost_usd=500.0)
+            assert tracker.cloud_allowed() is True
+
+    def test_low_daily_limit(self):
+        """Test with low daily limit."""
+        tracker = BudgetTracker(db_path=":memory:")
+        with patch("infrastructure.models.budget.settings") as mock_settings:
+            mock_settings.tier_cloud_daily_budget_usd = 1.0
+            mock_settings.tier_cloud_monthly_budget_usd = 100.0
+            tracker.record_spend("test", "model", cost_usd=2.0)
+            assert tracker.cloud_allowed() is False
+
+    def test_only_monthly_limit_enabled(self):
+        """Test with only monthly limit enabled."""
+        tracker = BudgetTracker(db_path=":memory:")
+        with patch("infrastructure.models.budget.settings") as mock_settings:
+            mock_settings.tier_cloud_daily_budget_usd = 0  # Disabled
+            mock_settings.tier_cloud_monthly_budget_usd = 50.0
+            tracker.record_spend("test", "model", cost_usd=30.0)
+            assert tracker.cloud_allowed() is True
+            tracker.record_spend("test", "model", cost_usd=25.0)
+            assert tracker.cloud_allowed() is False