Implement LLM-WP-0008: provider-scoped account balance CLI

Add pluggable balance registry, OpenRouter credits/key limit client,
and llm-connect balance with one-shot --provider that does not change
library defaults.

tests/test_balance.py

@@ -0,0 +1,141 @@
+import pytest
+
+from llm_connect.balance import (
+    AccountBalance,
+    BalanceClientRegistry,
+    OpenRouterBalanceClient,
+    format_balance_human,
+    get_account_balance,
+    resolve_balance_provider,
+)
+from llm_connect.config import LLMConfig
+from llm_connect.exceptions import LLMAPIError, LLMBalanceUnsupportedError, LLMConfigurationError
+from llm_connect.openrouter import _DEFAULT_MODEL as OPENROUTER_DEFAULT_MODEL
+
+
+def test_resolve_balance_provider_explicit_and_default():
+    assert resolve_balance_provider("OpenRouter") == "openrouter"
+    assert resolve_balance_provider(None) == LLMConfig().provider
+    assert resolve_balance_provider("") == LLMConfig().provider
+    assert resolve_balance_provider("  gemini  ") == "gemini"
+
+
+def test_resolve_balance_provider_does_not_mutate_defaults():
+    before_provider = LLMConfig().provider
+    before_model = OPENROUTER_DEFAULT_MODEL
+    resolve_balance_provider("gemini")
+    resolve_balance_provider("openai")
+    assert LLMConfig().provider == before_provider
+    assert OPENROUTER_DEFAULT_MODEL == before_model
+
+
+def test_registry_unsupported_provider():
+    registry = BalanceClientRegistry.default()
+    with pytest.raises(LLMBalanceUnsupportedError, match="gemini") as exc_info:
+        registry.create("gemini")
+    assert "openrouter" in exc_info.value.supported
+
+
+def test_openrouter_balance_client_maps_credits_and_key_limit():
+    def fake_get(url, headers=None, timeout=30):
+        if url.endswith("/credits"):
+            return {"data": {"total_credits": 25.0, "total_usage": 12.5}}
+        if url.endswith("/auth/key"):
+            return {
+                "data": {
+                    "limit": 10.0,
+                    "limit_remaining": 9.5,
+                    "limit_reset": "monthly",
+                    "usage": 1.5,
+                }
+            }
+        raise AssertionError(f"unexpected url {url}")
+
+    client = OpenRouterBalanceClient(
+        api_key="sk-test",
+        get_json_fn=fake_get,
+    )
+    balance = client.get_balance(fx=1.0)
+
+    assert balance.provider == "openrouter"
+    assert balance.credits_remaining == pytest.approx(12.5)
+    assert balance.credits_total == pytest.approx(25.0)
+    assert balance.credits_used == pytest.approx(12.5)
+    assert balance.limit_remaining == pytest.approx(9.5)
+    assert balance.limit == pytest.approx(10.0)
+    assert balance.limit_reset == "monthly"
+    assert balance.credits_remaining_eur == pytest.approx(12.5)
+    assert balance.limit_remaining_eur == pytest.approx(9.5)
+    assert "credits" in balance.source
+    assert "auth/key" in balance.source
+
+
+def test_openrouter_partial_failure_still_returns_one_signal():
+    def fake_get(url, headers=None, timeout=30):
+        if url.endswith("/credits"):
+            raise LLMAPIError("down", status_code=500)
+        if url.endswith("/auth/key"):
+            return {"data": {"limit": 5, "limit_remaining": 4, "limit_reset": "monthly"}}
+        raise AssertionError(url)
+
+    balance = OpenRouterBalanceClient(api_key="sk-test", get_json_fn=fake_get).get_balance(
+        fx=0.92
+    )
+    assert balance.credits_remaining is None
+    assert balance.limit_remaining == pytest.approx(4.0)
+    assert balance.limit_remaining_eur == pytest.approx(3.68)
+    assert "partial" in balance.source
+
+
+def test_openrouter_both_endpoints_fail():
+    def fake_get(url, headers=None, timeout=30):
+        raise LLMAPIError("nope", status_code=503)
+
+    with pytest.raises(LLMAPIError, match="both"):
+        OpenRouterBalanceClient(api_key="sk-test", get_json_fn=fake_get).get_balance()
+
+
+def test_openrouter_missing_key():
+    client = OpenRouterBalanceClient(api_key=None, get_json_fn=lambda *a, **k: {})
+    # Force empty key even if env has one
+    client._api_key = None
+    with pytest.raises(LLMConfigurationError, match="API key"):
+        client.get_balance()
+
+
+def test_get_account_balance_uses_registry():
+    class Stub:
+        provider_id = "stub"
+
+        def get_balance(self, *, fx=None):
+            return AccountBalance(
+                provider="stub",
+                currency="USD",
+                source="stub:test",
+                credits_remaining=1.0,
+            )
+
+    registry = BalanceClientRegistry({"stub": lambda: Stub()})
+    balance = get_account_balance("stub", registry=registry)
+    assert balance.credits_remaining == 1.0
+
+
+def test_format_balance_human_mentions_both_signals():
+    text = format_balance_human(
+        AccountBalance(
+            provider="openrouter",
+            currency="USD",
+            source="openrouter:/api/v1/credits+auth/key",
+            credits_remaining=12.5,
+            credits_remaining_eur=11.5,
+            limit_remaining=9.5,
+            limit_remaining_eur=8.74,
+            limit=10,
+            limit_reset="monthly",
+            fx_source="explicit",
+        )
+    )
+    assert "account credits remaining" in text
+    assert "key limit remaining" in text
+    assert "EUR" in text
+    assert "openrouter" in text