feat(ai): services partages A2 + SSE streaming B4 + confirmations UI B5 (#79)

backend/services/paths.py

@@ -0,0 +1,45 @@
+"""Vault path resolution shared by the REST routes and the AI tool layer.
+
+This is the single implementation of the anti path-traversal check. Routes map
+:class:`ServiceError` to ``HTTPException`` and tools map it to
+:class:`backend.tools.context.ToolError`.
+"""
+
+from __future__ import annotations
+
+import logging
+from pathlib import Path
+
+from backend.services.errors import ServiceError
+
+logger = logging.getLogger("obsigate.services.paths")
+
+
+def resolve_safe_path(vault_root: Path, relative_path: str | None) -> Path:
+    """Resolve a vault-relative path, rejecting traversal outside the vault.
+
+    Raises:
+        ServiceError: ``path_error`` (500) when the path cannot be resolved,
+            ``path_outside_vault`` (403) when it escapes the vault root.
+    """
+    full_path = vault_root / (relative_path or "")
+    try:
+        resolved = full_path.resolve(strict=False)
+        root = vault_root.resolve(strict=False)
+    except Exception as e:
+        logger.error(f"Path resolution error - vault_root: {vault_root}, relative_path: {relative_path}, error: {e}")
+        raise ServiceError(f"Path resolution error: {e!s}", code="path_error", status=500) from e
+
+    try:
+        resolved.relative_to(root)
+    except ValueError:
+        # Case-insensitive fallback for Windows / Docker path casing.
+        if not str(resolved).lower().startswith(str(root).lower()):
+            logger.warning(f"Path outside vault - vault: {root}, requested: {relative_path}, resolved: {resolved}")
+            raise ServiceError(
+                "Access denied: path outside vault",
+                code="path_outside_vault",
+                status=403,
+                details={"path": relative_path},
+            ) from None
+    return resolved