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>

llm_connect/claude_code.py

@@ -2,6 +2,7 @@
 Claude Code CLI adapter — runs the ``claude`` CLI as a subprocess.
 """
 
+import asyncio
 import subprocess
 from typing import Optional
 
@@ -35,6 +36,7 @@ class ClaudeCodeAdapter(LLMAdapter):
     # ── LLMAdapter interface ────────────────────────────────────────
 
     def execute_prompt(self, prompt: str, config: RunConfig) -> LLMResponse:
+        self._preflight_budget(config)
         cmd = [self._cli_path, "--print"]
         if self._model:
             cmd.extend(["--model", self._model])
@@ -66,7 +68,7 @@ class ClaudeCodeAdapter(LLMAdapter):
         prompt_tokens = estimate_tokens(prompt)
         completion_tokens = estimate_tokens(content)
 
-        return LLMResponse(
+        response = LLMResponse(
             content=content,
             model=self._model or "claude-code-cli",
             usage={
@@ -80,6 +82,63 @@ class ClaudeCodeAdapter(LLMAdapter):
                 "cli_path": self._cli_path,
             },
         )
+        self._consume_budget(config, response)
+        return response
+
+    async def async_execute_prompt(self, prompt: str, config: RunConfig) -> LLMResponse:
+        """Native async implementation using asyncio.create_subprocess_exec."""
+        self._preflight_budget(config)
+        cmd = [self._cli_path, "--print"]
+        if self._model:
+            cmd.extend(["--model", self._model])
+
+        timeout = config.timeout_seconds or self._config.timeout_seconds
+
+        try:
+            proc = await asyncio.create_subprocess_exec(
+                *cmd,
+                stdin=asyncio.subprocess.PIPE,
+                stdout=asyncio.subprocess.PIPE,
+                stderr=asyncio.subprocess.PIPE,
+            )
+            stdout_bytes, stderr_bytes = await asyncio.wait_for(
+                proc.communicate(input=prompt.encode()),
+                timeout=timeout,
+            )
+        except asyncio.TimeoutError as exc:
+            raise LLMTimeoutError(
+                f"claude CLI timed out after {timeout}s",
+                cause=exc,
+            ) from exc
+
+        if proc.returncode != 0:
+            raise LLMSubprocessError(
+                f"claude CLI exited with code {proc.returncode}",
+                return_code=proc.returncode,
+                stderr=stderr_bytes.decode(),
+            )
+
+        content = stdout_bytes.decode()
+        prompt_tokens = estimate_tokens(prompt)
+        completion_tokens = estimate_tokens(content)
+
+        response = LLMResponse(
+            content=content,
+            model=self._model or "claude-code-cli",
+            usage={
+                "prompt_tokens": prompt_tokens,
+                "completion_tokens": completion_tokens,
+                "total_tokens": prompt_tokens + completion_tokens,
+            },
+            finish_reason="stop",
+            metadata={
+                "provider": "claude-code",
+                "cli_path": self._cli_path,
+                "async": True,
+            },
+        )
+        self._consume_budget(config, response)
+        return response
 
     def validate_config(self, config: RunConfig) -> bool:
         try: