feat: WP-0001 foundation + WP-0002 core extensions

WP-0001 — Foundation & GAAF Baseline
- SCOPE.md, ARCHITECTURE-LAYERS.md, contracts/ tree
- .claude/rules/ stubs filled (architecture, stack, boundary)
- 57 tests (pytest), pyproject.toml with ruff+mypy, CI workflow

WP-0002 — Core Extensions (FR-4 + FR-3)
- FR-4: BudgetTracker (thread-safe) + LLMBudgetExceededError +
  optional RunConfig.budget_tracker + enforcement in all adapters
- FR-3: async_execute_prompt on LLMAdapter ABC (asyncio.to_thread
  fallback) + native asyncio.create_subprocess_exec in ClaudeCodeAdapter

81 tests passing.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

tests/test_exceptions.py

@@ -0,0 +1,96 @@
+"""
+Tests for the LLMError exception hierarchy (Core).
+"""
+
+import pytest
+from llm_connect.exceptions import (
+    LLMError,
+    LLMConfigurationError,
+    LLMAPIError,
+    LLMRateLimitError,
+    LLMTimeoutError,
+    LLMSubprocessError,
+)
+
+
+class TestLLMErrorHierarchy:
+    def test_all_are_subclasses_of_llm_error(self):
+        assert issubclass(LLMConfigurationError, LLMError)
+        assert issubclass(LLMAPIError, LLMError)
+        assert issubclass(LLMRateLimitError, LLMError)
+        assert issubclass(LLMTimeoutError, LLMError)
+        assert issubclass(LLMSubprocessError, LLMError)
+
+    def test_rate_limit_is_api_error(self):
+        assert issubclass(LLMRateLimitError, LLMAPIError)
+
+    def test_all_are_exceptions(self):
+        assert issubclass(LLMError, Exception)
+
+
+class TestLLMError:
+    def test_basic_message(self):
+        err = LLMError("something went wrong")
+        assert str(err) == "something went wrong"
+
+    def test_context_appears_in_str(self):
+        err = LLMError("oops", context={"provider": "openai"})
+        assert "provider=openai" in str(err)
+
+    def test_cause_is_chained(self):
+        cause = ValueError("root cause")
+        err = LLMError("wrapper", cause=cause)
+        assert err.__cause__ is cause
+
+    def test_empty_context_does_not_appear(self):
+        err = LLMError("clean message", context={})
+        assert str(err) == "clean message"
+
+
+class TestLLMAPIError:
+    def test_has_status_code(self):
+        err = LLMAPIError("bad request", status_code=400)
+        assert err.status_code == 400
+
+    def test_has_response_body(self):
+        err = LLMAPIError("error", status_code=500, response_body='{"error": "oops"}')
+        assert err.response_body == '{"error": "oops"}'
+
+    def test_defaults(self):
+        err = LLMAPIError("minimal")
+        assert err.status_code == 0
+        assert err.response_body == ""
+
+    def test_rate_limit_inherits_status_code(self):
+        err = LLMRateLimitError("too many", status_code=429)
+        assert err.status_code == 429
+        assert isinstance(err, LLMAPIError)
+
+
+class TestLLMSubprocessError:
+    def test_has_return_code(self):
+        err = LLMSubprocessError("cli failed", return_code=1)
+        assert err.return_code == 1
+
+    def test_has_stderr(self):
+        err = LLMSubprocessError("cli failed", stderr="error output")
+        assert err.stderr == "error output"
+
+    def test_defaults(self):
+        err = LLMSubprocessError("minimal")
+        assert err.return_code == 1
+        assert err.stderr == ""
+
+
+class TestRaiseAndCatch:
+    def test_catch_as_llm_error(self):
+        with pytest.raises(LLMError):
+            raise LLMConfigurationError("no key")
+
+    def test_catch_api_error_as_llm_error(self):
+        with pytest.raises(LLMError):
+            raise LLMAPIError("http error", status_code=502)
+
+    def test_catch_rate_limit_as_api_error(self):
+        with pytest.raises(LLMAPIError):
+            raise LLMRateLimitError("429", status_code=429)