feat: implement built-in file system tools (#18)

CLAUDE.md

@@ -54,7 +54,7 @@ src/ai_company/
   providers/      # LLM provider abstraction (LiteLLM adapter)
   security/       # SecOps agent, approval gates, audit
   templates/      # Pre-built company templates and builder
-  tools/          # Tool registry, MCP integration, role-based access, sandboxing
+  tools/          # Tool registry, MCP integration, role-based access, built-in tools (file_system/)
 ```
 
 ## Shell Usage

DESIGN_SPEC.md

@@ -2344,7 +2344,15 @@ ai-company/
 │       │   │   ├── protocol.py    # SandboxBackend protocol
 │       │   │   ├── subprocess.py  # SubprocessSandbox (default for low-risk)
 │       │   │   └── docker.py      # DockerSandbox (for code_runner, terminal)
-│       │   ├── file_system.py      # File operations (M3)
+│       │   ├── file_system/        # Built-in file system tools
+│       │   │   ├── __init__.py    # Package exports
+│       │   │   ├── _base_fs_tool.py  # BaseFileSystemTool ABC
+│       │   │   ├── _path_validator.py # Workspace path validation
+│       │   │   ├── delete_file.py # DeleteFileTool
+│       │   │   ├── edit_file.py   # EditFileTool
+│       │   │   ├── list_directory.py # ListDirectoryTool
+│       │   │   ├── read_file.py   # ReadFileTool
+│       │   │   └── write_file.py  # WriteFileTool
 │       │   ├── git_tools.py        # Git operations (M3)
 │       │   ├── code_runner.py      # Code execution (M3)
 │       │   ├── web_tools.py        # HTTP, search (M3)
@@ -2427,7 +2435,7 @@ These conventions were established during the M0–M2+ review cycle. **Adopted**
 | **Event constants** | Adopted (per-domain) | Per-domain submodules under `events/` package (e.g. `events.provider`, `events.budget`). Import directly: `from ai_company.observability.events.<domain> import CONSTANT` | Split by domain for discoverability, co-location with domain logic, and reduced merge conflicts as constants grow. `__init__.py` serves as package marker with usage documentation; no re-exports. |
 | **Parallel tool execution** | Adopted (M2.5) | `asyncio.TaskGroup` in `ToolInvoker.invoke_all` with optional `max_concurrency` semaphore | Structured concurrency with proper cancellation semantics. Fatal errors collected via guarded wrapper and re-raised after all tasks complete. |
 | **Tool permission checking** | Adopted (M3) | `ToolPermissionChecker` enforces category-level gating based on `ToolAccessLevel` (sandboxed → restricted → standard → elevated, plus custom). Priority-based resolution: denied list → allowed list → level categories → deny. Case-insensitive name matching. `ToolInvoker` filters definitions for prompt and checks at invocation time. | Defense-in-depth: agents only see permitted tools in the LLM prompt, and invocations are re-checked at execution time. Explicit allow/deny lists provide per-agent overrides. See §11.1.1. |
-| **Tool sandboxing** | Planned (M3) | Layered `SandboxBackend` protocol: `SubprocessSandbox` for low-risk tools (file, git), `DockerSandbox` for high-risk tools (code_runner, terminal, web, database). `K8sSandbox` planned for future container deployments. | Risk-proportionate isolation. Docker optional — only needed for code execution and network-sensitive tools. Pluggable protocol enables seamless migration to K8s per-agent pods in Phase 3-4. See §11.1.2. |
+| **Tool sandboxing** | Partial (M3) | File system tools use in-process `PathValidator` for workspace-scoped path validation (symlink resolution + containment check). `BaseFileSystemTool` ABC provides shared `ToolCategory.FILE_SYSTEM` and `PathValidator` integration — all file system tools extend this base. `SandboxBackend` protocol with `SubprocessSandbox` / `DockerSandbox` remains planned for git, code_runner, terminal, web, and database tools. `K8sSandbox` planned for future container deployments. | File system tools use defence-in-depth path validation; heavier sandbox isolation reserved for higher-risk tool categories (code execution, network). See §11.1.2. |
 | **Crash recovery** | Planned (M3) | Pluggable `RecoveryStrategy` protocol. M3: `FailAndReassignStrategy` (catch at engine boundary, log snapshot, mark FAILED, reassign). M4/M5: `CheckpointStrategy` (persist `AgentContext` per turn, resume from last checkpoint). | Immutable `model_copy` pattern makes checkpoint serialization trivial to add later. Fail-and-reassign is sufficient for short MVP tasks. See §6.6. |
 | **Agent behavior testing** | Planned (M3) | Scripted `FakeProvider` for unit tests (deterministic turn sequences); behavioral outcome assertions for integration tests (task completed, tools called, cost within budget). | Leverages existing `FakeProvider` and `CompletionResponseFactory` fixtures. Precise engine testing without brittle response-matching at integration level. |
 | **LLM call analytics** | Planned (incremental) | M3: proxy metrics (`turns_per_task`, `tokens_per_task`). M4: call categorization (`productive`, `coordination`, `system`) + orchestration ratio. M5+: full analytics (retry tracking, latency, cache hits, per-provider comparison). | Append-only, never blocks execution. Builds on existing `CostRecord` infrastructure. Detects orchestration overhead early. See §10.5. |

src/ai_company/observability/events/tool.py

@@ -22,3 +22,20 @@
 TOOL_PERMISSION_DENIED: Final[str] = "tool.permission.denied"
 TOOL_PERMISSION_CHECKER_CREATED: Final[str] = "tool.permission.checker_created"
 TOOL_PERMISSION_FILTERED: Final[str] = "tool.permission.filtered"
+
+# ── File system tool events ──────────────────────────────────────
+TOOL_FS_READ: Final[str] = "tool.fs.read"
+TOOL_FS_WRITE: Final[str] = "tool.fs.write"
+TOOL_FS_EDIT: Final[str] = "tool.fs.edit"
+TOOL_FS_EDIT_NOT_FOUND: Final[str] = "tool.fs.edit_not_found"
+TOOL_FS_LIST: Final[str] = "tool.fs.list"
+TOOL_FS_DELETE: Final[str] = "tool.fs.delete"
+TOOL_FS_PATH_VIOLATION: Final[str] = "tool.fs.path_violation"
+TOOL_FS_BINARY_DETECTED: Final[str] = "tool.fs.binary_detected"
+TOOL_FS_SIZE_EXCEEDED: Final[str] = "tool.fs.size_exceeded"
+TOOL_FS_ERROR: Final[str] = "tool.fs.error"
+TOOL_FS_STAT_FAILED: Final[str] = "tool.fs.stat_failed"
+TOOL_FS_WORKSPACE_INVALID: Final[str] = "tool.fs.workspace_invalid"
+TOOL_FS_PARENT_NOT_FOUND: Final[str] = "tool.fs.parent_not_found"
+TOOL_FS_GLOB_REJECTED: Final[str] = "tool.fs.glob_rejected"
+TOOL_FS_NOOP: Final[str] = "tool.fs.noop"

src/ai_company/tools/__init__.py

@@ -9,13 +9,28 @@
     ToolPermissionDeniedError,
 )
 from .examples.echo import EchoTool
+from .file_system import (
+    BaseFileSystemTool,
+    DeleteFileTool,
+    EditFileTool,
+    ListDirectoryTool,
+    PathValidator,
+    ReadFileTool,
+    WriteFileTool,
+)
 from .invoker import ToolInvoker
 from .permissions import ToolPermissionChecker
 from .registry import ToolRegistry
 
 __all__ = [
+    "BaseFileSystemTool",
     "BaseTool",
+    "DeleteFileTool",
     "EchoTool",
+    "EditFileTool",
+    "ListDirectoryTool",
+    "PathValidator",
+    "ReadFileTool",
     "ToolError",
     "ToolExecutionError",
     "ToolExecutionResult",
@@ -25,4 +40,5 @@
     "ToolPermissionChecker",
     "ToolPermissionDeniedError",
     "ToolRegistry",
+    "WriteFileTool",
 ]

src/ai_company/tools/file_system/__init__.py

@@ -0,0 +1,23 @@
+"""Built-in file system tools for workspace interaction.
+
+Provides tools for reading, writing, editing, listing, and deleting
+files within a sandboxed workspace directory.
+"""
+
+from ai_company.tools.file_system._base_fs_tool import BaseFileSystemTool
+from ai_company.tools.file_system._path_validator import PathValidator
+from ai_company.tools.file_system.delete_file import DeleteFileTool
+from ai_company.tools.file_system.edit_file import EditFileTool
+from ai_company.tools.file_system.list_directory import ListDirectoryTool
+from ai_company.tools.file_system.read_file import ReadFileTool
+from ai_company.tools.file_system.write_file import WriteFileTool
+
+__all__ = [
+    "BaseFileSystemTool",
+    "DeleteFileTool",
+    "EditFileTool",
+    "ListDirectoryTool",
+    "PathValidator",
+    "ReadFileTool",
+    "WriteFileTool",
+]

src/ai_company/tools/file_system/_base_fs_tool.py

@@ -0,0 +1,80 @@
+"""Base class for file system tools.
+
+Provides the common ``ToolCategory.FILE_SYSTEM`` category and a
+``PathValidator`` instance bound to the workspace root.
+"""
+
+from abc import ABC
+from typing import TYPE_CHECKING, Any
+
+from ai_company.core.enums import ToolCategory
+from ai_company.observability import get_logger
+from ai_company.tools.base import BaseTool
+from ai_company.tools.file_system._path_validator import PathValidator
+
+if TYPE_CHECKING:
+    from pathlib import Path
+
+logger = get_logger(__name__)
+
+
+def _map_os_error(exc: OSError, user_path: str, verb: str) -> tuple[str, str]:
+    """Map an OS error to ``(log_key, user_message)`` for FS operations.
+
+    Args:
+        exc: The caught OS-level exception.
+        user_path: The original user-supplied path string.
+        verb: Action verb for the fallback message (e.g. ``"reading"``).
+
+    Returns:
+        A two-tuple of (structured log key, human-readable message).
+    """
+    if isinstance(exc, FileNotFoundError):
+        return "not_found", f"File not found: {user_path}"
+    if isinstance(exc, IsADirectoryError):
+        return "is_directory", f"Path is a directory, not a file: {user_path}"
+    if isinstance(exc, PermissionError):
+        return "permission_denied", f"Permission denied: {user_path}"
+    return str(exc), f"OS error {verb} file: {user_path}"
+
+
+class BaseFileSystemTool(BaseTool, ABC):
+    """Abstract base for all file system tools.
+
+    Sets ``category=ToolCategory.FILE_SYSTEM`` and holds a shared
+    ``PathValidator`` for workspace-scoped path resolution.
+    """
+
+    def __init__(
+        self,
+        *,
+        workspace_root: Path,
+        name: str,
+        description: str = "",
+        parameters_schema: dict[str, Any] | None = None,
+    ) -> None:
+        """Initialize with a workspace root and tool metadata.
+
+        Args:
+            workspace_root: Root directory bounding file access.
+            name: Tool name.
+            description: Human-readable description.
+            parameters_schema: JSON Schema for tool parameters.
+        """
+        super().__init__(
+            name=name,
+            description=description,
+            category=ToolCategory.FILE_SYSTEM,
+            parameters_schema=parameters_schema,
+        )
+        self._path_validator = PathValidator(workspace_root)
+
+    @property
+    def workspace_root(self) -> Path:
+        """The resolved workspace root directory."""
+        return self._path_validator.workspace_root
+
+    @property
+    def path_validator(self) -> PathValidator:
+        """The path validator instance."""
+        return self._path_validator

src/ai_company/tools/file_system/_path_validator.py

@@ -0,0 +1,109 @@
+"""Workspace path validation for file system tools.
+
+All file system tools delegate path validation to ``PathValidator``,
+which ensures that resolved paths remain within the configured
+workspace root.  This prevents path-traversal attacks via ``../``,
+symlinks, or absolute paths outside the workspace.
+"""
+
+from typing import TYPE_CHECKING
+
+from ai_company.observability import get_logger
+from ai_company.observability.events.tool import (
+    TOOL_FS_PARENT_NOT_FOUND,
+    TOOL_FS_PATH_VIOLATION,
+    TOOL_FS_WORKSPACE_INVALID,
+)
+
+if TYPE_CHECKING:
+    from pathlib import Path
+
+logger = get_logger(__name__)
+
+
+class PathValidator:
+    """Validates and resolves paths against a workspace root.
+
+    All resolved paths must remain within ``workspace_root``.
+    Symlinks are resolved before checking, so a symlink pointing
+    outside the workspace is rejected.
+
+    Attributes:
+        workspace_root: The resolved workspace root directory.
+    """
+
+    def __init__(self, workspace_root: Path) -> None:
+        """Initialize with a workspace root directory.
+
+        Args:
+            workspace_root: Root directory that bounds all file access.
+
+        Raises:
+            ValueError: If workspace_root does not exist or is not a
+                directory.
+        """
+        resolved = workspace_root.resolve()
+        if not resolved.is_dir():
+            logger.warning(
+                TOOL_FS_WORKSPACE_INVALID,
+                workspace_root=str(workspace_root),
+            )
+            msg = f"Workspace root is not an existing directory: {workspace_root}"
+            raise ValueError(msg)
+        self._workspace_root = resolved
+
+    @property
+    def workspace_root(self) -> Path:
+        """The resolved workspace root directory."""
+        return self._workspace_root
+
+    def validate(self, path: str) -> Path:
+        """Resolve *path* against workspace root and validate containment.
+
+        Args:
+            path: A relative or absolute path string from the user.
+
+        Returns:
+            The resolved ``Path`` guaranteed to be within the workspace.
+
+        Raises:
+            ValueError: If the resolved path escapes the workspace.
+        """
+        # NOTE: There is an inherent TOCTOU gap between this validation
+        # and the actual file operation (which runs in asyncio.to_thread).
+        # A concurrent process could swap in a symlink between validation
+        # and use.  Full mitigation requires OS-level sandboxing (e.g.
+        # openat2 RESOLVE_BENEATH on Linux).  User-space path validation
+        # is a best-effort defence-in-depth layer.
+        resolved = (self._workspace_root / path).resolve()
+        if not resolved.is_relative_to(self._workspace_root):
+            logger.warning(
+                TOOL_FS_PATH_VIOLATION,
+                user_path=path,
+            )
+            msg = f"Path escapes workspace: {path}"
+            raise ValueError(msg)
+        return resolved
+
+    def validate_parent_exists(self, path: str) -> Path:
+        """Like ``validate`` but also checks that the parent directory exists.
+
+        Args:
+            path: A relative or absolute path string from the user.
+
+        Returns:
+            The resolved ``Path`` within the workspace whose parent exists.
+
+        Raises:
+            ValueError: If the resolved path escapes the workspace or
+                the parent directory does not exist.
+        """
+        resolved = self.validate(path)
+        if not resolved.parent.exists():
+            logger.warning(
+                TOOL_FS_PARENT_NOT_FOUND,
+                path=path,
+            )
+            msg = f"Parent directory does not exist: {path}"
+            raise ValueError(msg)
+        return resolved