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_async.py

@@ -0,0 +1,101 @@
+"""
+Tests for async_execute_prompt (FR-3).
+"""
+
+import asyncio
+import pytest
+
+from llm_connect.models import RunConfig, BudgetTracker
+from llm_connect.adapter import MockLLMAdapter
+from llm_connect.exceptions import LLMBudgetExceededError
+
+
+class TestAsyncExecutePrompt:
+    def test_default_fallback_returns_response(self):
+        adapter = MockLLMAdapter(mock_response="async result")
+        config = RunConfig()
+        response = asyncio.run(adapter.async_execute_prompt("hello", config))
+        assert response.content == "async result"
+
+    def test_gather_multiple_adapters(self):
+        """asyncio.gather over N adapters completes without errors."""
+        adapters = [MockLLMAdapter(mock_response=f"resp-{i}") for i in range(4)]
+        config = RunConfig()
+
+        async def run():
+            return await asyncio.gather(*[
+                a.async_execute_prompt("prompt", config) for a in adapters
+            ])
+
+        results = asyncio.run(run())
+        assert len(results) == 4
+        for i, r in enumerate(results):
+            assert r.content == f"resp-{i}"
+
+    def test_gather_increments_call_counts(self):
+        adapter = MockLLMAdapter()
+        config = RunConfig()
+
+        async def run():
+            await asyncio.gather(*[
+                adapter.async_execute_prompt("p", config) for _ in range(5)
+            ])
+
+        asyncio.run(run())
+        assert adapter.call_count == 5
+
+    def test_concurrent_faster_than_sequential(self):
+        """Gathering N async calls should not be N× slower than one call."""
+        import time
+
+        adapter = MockLLMAdapter()
+        config = RunConfig()
+
+        async def run_concurrent(n: int):
+            await asyncio.gather(*[
+                adapter.async_execute_prompt("p", config) for _ in range(n)
+            ])
+
+        # Just verify it completes without deadlock or error — timing is CI-unreliable
+        asyncio.run(run_concurrent(10))
+        assert adapter.call_count == 10
+
+    def test_async_with_budget_tracker(self):
+        """Budget enforcement works through async calls."""
+        tracker = BudgetTracker(total=10000)
+        config = RunConfig(budget_tracker=tracker)
+        adapter = MockLLMAdapter(mock_response="hi")
+
+        asyncio.run(adapter.async_execute_prompt("hello", config))
+        assert tracker.spent > 0
+
+    def test_async_exhausted_budget_raises(self):
+        """Exhausted budget raises LLMBudgetExceededError in async context."""
+        tracker = BudgetTracker(total=1)
+        tracker.consume(1)
+        config = RunConfig(budget_tracker=tracker)
+        adapter = MockLLMAdapter()
+
+        with pytest.raises(LLMBudgetExceededError):
+            asyncio.run(adapter.async_execute_prompt("p", config))
+
+    def test_async_gather_with_shared_budget(self):
+        """Shared budget across concurrent async calls is enforced correctly."""
+        tracker = BudgetTracker(total=100000)
+        config = RunConfig(budget_tracker=tracker)
+        adapters = [MockLLMAdapter(mock_response="hi") for _ in range(4)]
+
+        async def run():
+            await asyncio.gather(*[
+                a.async_execute_prompt("hello", config) for a in adapters
+            ])
+
+        asyncio.run(run())
+        assert tracker.spent > 0
+
+    def test_returns_llm_response_type(self):
+        from llm_connect.models import LLMResponse
+        adapter = MockLLMAdapter()
+        config = RunConfig()
+        response = asyncio.run(adapter.async_execute_prompt("q", config))
+        assert isinstance(response, LLMResponse)