fix(security): apply file safety to copilot acp fs

agent/copilot_acp_client.py

@@ -21,6 +21,9 @@ from pathlib import Path
 from types import SimpleNamespace
 from typing import Any
 
+from agent.file_safety import get_read_block_error, is_write_denied
+from agent.redact import redact_sensitive_text
+
 ACP_MARKER_BASE_URL = "acp://copilot"
 _DEFAULT_TIMEOUT_SECONDS = 900.0
 
@@ -54,6 +57,18 @@ def _jsonrpc_error(message_id: Any, code: int, message: str) -> dict[str, Any]:
     }
 
 
+def _permission_denied(message_id: Any) -> dict[str, Any]:
+    return {
+        "jsonrpc": "2.0",
+        "id": message_id,
+        "result": {
+            "outcome": {
+                "outcome": "cancelled",
+            }
+        },
+    }
+
+
 def _format_messages_as_prompt(
     messages: list[dict[str, Any]],
     model: str | None = None,
@@ -535,18 +550,13 @@ class CopilotACPClient:
         params = msg.get("params") or {}
 
         if method == "session/request_permission":
-            response = {
-                "jsonrpc": "2.0",
-                "id": message_id,
-                "result": {
-                    "outcome": {
-                        "outcome": "allow_once",
-                    }
-                },
-            }
+            response = _permission_denied(message_id)
         elif method == "fs/read_text_file":
             try:
                 path = _ensure_path_within_cwd(str(params.get("path") or ""), cwd)
+                block_error = get_read_block_error(str(path))
+                if block_error:
+                    raise PermissionError(block_error)
                 content = path.read_text() if path.exists() else ""
                 line = params.get("line")
                 limit = params.get("limit")
@@ -555,6 +565,8 @@ class CopilotACPClient:
                     start = line - 1
                     end = start + limit if isinstance(limit, int) and limit > 0 else None
                     content = "".join(lines[start:end])
+                if content:
+                    content = redact_sensitive_text(content)
                 response = {
                     "jsonrpc": "2.0",
                     "id": message_id,
@@ -567,6 +579,10 @@ class CopilotACPClient:
         elif method == "fs/write_text_file":
             try:
                 path = _ensure_path_within_cwd(str(params.get("path") or ""), cwd)
+                if is_write_denied(str(path)):
+                    raise PermissionError(
+                        f"Write denied: '{path}' is a protected system/credential file."
+                    )
                 path.parent.mkdir(parents=True, exist_ok=True)
                 path.write_text(str(params.get("content") or ""))
                 response = {

agent/file_safety.py

@@ -0,0 +1,111 @@
+"""Shared file safety rules used by both tools and ACP shims."""
+
+from __future__ import annotations
+
+import os
+from pathlib import Path
+from typing import Optional
+
+
+def _hermes_home_path() -> Path:
+    """Resolve the active HERMES_HOME (profile-aware) without circular imports."""
+    try:
+        from hermes_constants import get_hermes_home  # local import to avoid cycles
+        return get_hermes_home()
+    except Exception:
+        return Path(os.path.expanduser("~/.hermes"))
+
+
+def build_write_denied_paths(home: str) -> set[str]:
+    """Return exact sensitive paths that must never be written."""
+    hermes_home = _hermes_home_path()
+    return {
+        os.path.realpath(p)
+        for p in [
+            os.path.join(home, ".ssh", "authorized_keys"),
+            os.path.join(home, ".ssh", "id_rsa"),
+            os.path.join(home, ".ssh", "id_ed25519"),
+            os.path.join(home, ".ssh", "config"),
+            str(hermes_home / ".env"),
+            os.path.join(home, ".bashrc"),
+            os.path.join(home, ".zshrc"),
+            os.path.join(home, ".profile"),
+            os.path.join(home, ".bash_profile"),
+            os.path.join(home, ".zprofile"),
+            os.path.join(home, ".netrc"),
+            os.path.join(home, ".pgpass"),
+            os.path.join(home, ".npmrc"),
+            os.path.join(home, ".pypirc"),
+            "/etc/sudoers",
+            "/etc/passwd",
+            "/etc/shadow",
+        ]
+    }
+
+
+def build_write_denied_prefixes(home: str) -> list[str]:
+    """Return sensitive directory prefixes that must never be written."""
+    return [
+        os.path.realpath(p) + os.sep
+        for p in [
+            os.path.join(home, ".ssh"),
+            os.path.join(home, ".aws"),
+            os.path.join(home, ".gnupg"),
+            os.path.join(home, ".kube"),
+            "/etc/sudoers.d",
+            "/etc/systemd",
+            os.path.join(home, ".docker"),
+            os.path.join(home, ".azure"),
+            os.path.join(home, ".config", "gh"),
+        ]
+    ]
+
+
+def get_safe_write_root() -> Optional[str]:
+    """Return the resolved HERMES_WRITE_SAFE_ROOT path, or None if unset."""
+    root = os.getenv("HERMES_WRITE_SAFE_ROOT", "")
+    if not root:
+        return None
+    try:
+        return os.path.realpath(os.path.expanduser(root))
+    except Exception:
+        return None
+
+
+def is_write_denied(path: str) -> bool:
+    """Return True if path is blocked by the write denylist or safe root."""
+    home = os.path.realpath(os.path.expanduser("~"))
+    resolved = os.path.realpath(os.path.expanduser(str(path)))
+
+    if resolved in build_write_denied_paths(home):
+        return True
+    for prefix in build_write_denied_prefixes(home):
+        if resolved.startswith(prefix):
+            return True
+
+    safe_root = get_safe_write_root()
+    if safe_root and not (resolved == safe_root or resolved.startswith(safe_root + os.sep)):
+        return True
+
+    return False
+
+
+def get_read_block_error(path: str) -> Optional[str]:
+    """Return an error message when a read targets internal Hermes cache files."""
+    resolved = Path(path).expanduser().resolve()
+    hermes_home = _hermes_home_path().resolve()
+    blocked_dirs = [
+        hermes_home / "skills" / ".hub" / "index-cache",
+        hermes_home / "skills" / ".hub",
+    ]
+    for blocked in blocked_dirs:
+        try:
+            resolved.relative_to(blocked)
+        except ValueError:
+            continue
+        return (
+            f"Access denied: {path} is an internal Hermes cache file "
+            "and cannot be read directly to prevent prompt injection. "
+            "Use the skills_list or skill_view tools instead."
+        )
+    return None