feat(mcp): add Result-returning variants of resolve, read, list, search

Strictly additive: existing _resolve_and_check, read_file, list_directory,
and search_files are unchanged. The new variants return Result[Path] or
Result[str] using the data-oriented ErrorInfo/ErrorKind convention.

src/mcp_client.py

@@ -72,6 +72,7 @@ from src import beads_client
 from src import models
 from src import outline_tool
 from src import summarize
+from src.result_types import ErrorInfo, ErrorKind, NilPath, Result
 
 
 # ------------------------------------------------------------------ mutating tools sentinel
@@ -265,6 +266,104 @@ def read_file(path: str) -> str:
  except Exception as e:
   return f"ERROR reading '{path}': {e}"
 
+#region: Result Variants
+def _resolve_and_check_result(raw_path: str) -> Result[Path]:
+ try:
+  p = Path(raw_path)
+  if not p.is_absolute() and _primary_base_dir:
+   p = _primary_base_dir / p
+  p = p.resolve()
+ except Exception as e:
+  return Result(
+   data=NilPath(),
+   errors=[ErrorInfo(kind=ErrorKind.INVALID_INPUT, message=str(e), source="mcp._resolve_and_check_result", original=e)],
+  )
+ if not _is_allowed(p):
+  allowed_bases = "\n".join([f"  - {d}" for d in _base_dirs])
+  return Result(
+   data=NilPath(),
+   errors=[ErrorInfo(
+    kind=ErrorKind.PERMISSION,
+    message=f"path '{raw_path}' resolves to '{p}', which is not within the allowed paths.\nAllowed base directories are:\n{allowed_bases}",
+    source="mcp._resolve_and_check_result",
+   )],
+  )
+ return Result(data=p)
+
+def read_file_result(path: str) -> Result[str]:
+ resolved = _resolve_and_check_result(path)
+ if not resolved.ok:
+  return Result(data="", errors=resolved.errors)
+ p = resolved.data
+ if isinstance(p, NilPath):
+  return Result(data="", errors=resolved.errors)
+ if not p.exists():
+  return Result(data="", errors=[ErrorInfo(kind=ErrorKind.NOT_FOUND, message=f"file not found: {path}", source="mcp.read_file_result")])
+ if not p.is_file():
+  return Result(data="", errors=[ErrorInfo(kind=ErrorKind.INVALID_INPUT, message=f"not a file: {path}", source="mcp.read_file_result")])
+ try:
+  content = p.read_text(encoding="utf-8")
+  return Result(data=content)
+ except Exception as e:
+  return Result(data="", errors=[ErrorInfo(kind=ErrorKind.INTERNAL, message=str(e), source="mcp.read_file_result", original=e)])
+
+def list_directory_result(path: str) -> Result[str]:
+ resolved = _resolve_and_check_result(path)
+ if not resolved.ok:
+  return Result(data="", errors=resolved.errors)
+ p = resolved.data
+ if isinstance(p, NilPath):
+  return Result(data="", errors=resolved.errors)
+ if not p.exists():
+  return Result(data="", errors=[ErrorInfo(kind=ErrorKind.NOT_FOUND, message=f"path not found: {path}", source="mcp.list_directory_result")])
+ if not p.is_dir():
+  return Result(data="", errors=[ErrorInfo(kind=ErrorKind.INVALID_INPUT, message=f"not a directory: {path}", source="mcp.list_directory_result")])
+ try:
+  entries = sorted(p.iterdir(), key=lambda e: (e.is_file(), e.name.lower()))
+  lines = [f"Directory: {p}", ""]
+  count = 0
+  for entry in entries:
+   name = entry.name.lower()
+   if name == "history.toml" or name.endswith("_history.toml"):
+    continue
+   kind = "file" if entry.is_file() else "dir "
+   size = f"{entry.stat().st_size:>10,} bytes" if entry.is_file() else ""
+   lines.append(f"  [{kind}]  {entry.name:<40}  {size}")
+   count += 1
+  lines.append(f"  ({count} entries)")
+  return Result(data="\n".join(lines))
+ except Exception as e:
+  return Result(data="", errors=[ErrorInfo(kind=ErrorKind.INTERNAL, message=str(e), source="mcp.list_directory_result", original=e)])
+
+def search_files_result(path: str, pattern: str) -> Result[str]:
+ resolved = _resolve_and_check_result(path)
+ if not resolved.ok:
+  return Result(data="", errors=resolved.errors)
+ p = resolved.data
+ if isinstance(p, NilPath):
+  return Result(data="", errors=resolved.errors)
+ if not p.is_dir():
+  return Result(data="", errors=[ErrorInfo(kind=ErrorKind.INVALID_INPUT, message=f"not a directory: {path}", source="mcp.search_files_result")])
+ try:
+  matches = sorted(p.glob(pattern))
+  if not matches:
+   return Result(data=f"No files matched '{pattern}' in {path}")
+  lines = [f"Search '{pattern}' in {p}:", ""]
+  count = 0
+  for m in matches:
+   name = m.name.lower()
+   if name == "history.toml" or name.endswith("_history.toml"):
+    continue
+   rel = m.relative_to(p)
+   kind = "file" if m.is_file() else "dir "
+   lines.append(f"  [{kind}]  {rel}")
+   count += 1
+  lines.append(f"  ({count} match(es))")
+  return Result(data="\n".join(lines))
+ except Exception as e:
+  return Result(data="", errors=[ErrorInfo(kind=ErrorKind.INTERNAL, message=str(e), source="mcp.search_files_result", original=e)])
+#endregion: Result Variants
+
 def edit_file(path: str, old_string: str, new_string: str, replace_all: bool = False) -> str:
  """
  Replace exact string match in a file. Preserves indentation and line endings.