lib.FileContext: Add readdir() method

FileContext offers get(), put(), unlink(), mkdir(), and stat(), but no way
to list the entries of a directory, so consumers that need the names of the
entries under a path in a context have no portable means to obtain them.

Add readdir(), returning Iterable[str], following the _readdir() ->
readdir() pattern used by the other operations: the public method chroots
the path via _chroot() and delegates to the _readdir() hook, which raises
NotImplementedError by default.

Implement _readdir() in the context families:

- Local._readdir(): os.listdir()
- ExecContext._readdir(): runs ls -1A and splits the output into one entry
  per line; inherited by SSHClient and the other command-based contexts
- Curl._readdir(): raises OSError with errno.ENOSYS

Add unit tests covering Local (listing, hidden entries, missing directory)
and Curl (ENOSYS).

Assisted-by: unsloth/Qwen3.8-27B-GGUF:Q4_K_M with pi.dev v0.87.1
Signed-off-by: Jan Lindemann <jan@janware.com>

src/python/jw/pkg/lib/ExecContext.py

@@ -5,7 +5,7 @@ import errno
 import sys
 
 from decimal import ROUND_FLOOR, Decimal
-from typing import TYPE_CHECKING, Any, NamedTuple, override
+from typing import TYPE_CHECKING, Any, Iterable, NamedTuple, override
 
 if TYPE_CHECKING:
     from typing import Type
@@ -688,3 +688,10 @@ class ExecContext(Base):
             ['chmod', self.__mode_str(mode), path],
             cmd_input = InputMode.NonInteractive
         )
+
+    @override
+    async def _readdir(self, path: str) -> Iterable[str]:
+        result = await self.run(
+            ['ls', '-1A', path], cmd_input = InputMode.NonInteractive
+        )
+        return result.stdout_str.splitlines()

src/python/jw/pkg/lib/FileContext.py

@@ -4,7 +4,7 @@ import abc
 
 from enum import Enum, auto
 from functools import cached_property
-from typing import TYPE_CHECKING, Any, override
+from typing import TYPE_CHECKING, Any, Iterable, override
 
 from .log import DEBUG, ERR, log
 from .ProcFilter import ProcPipeline
@@ -301,6 +301,14 @@ class FileContext(abc.ABC):
     async def is_dir(self, path: str, follow_symlinks: bool = True) -> bool:
         return await self._is_dir(self._chroot(path), follow_symlinks = follow_symlinks)
 
+    async def _readdir(self, path: str) -> Iterable[str]:
+        raise NotImplementedError(
+            f'{self.log_name}: readdir("{path}") is not implemented'
+        )
+
+    async def readdir(self, path: str) -> Iterable[str]:
+        return await self._readdir(self._chroot(path))
+
     @classmethod
     def create(cls, uri: str | Uri, *args: Any, **kwargs: Any) -> 'FileContext':
         uri = Uri.pimp(uri)

src/python/jw/pkg/lib/ec/Curl.py

@@ -1,6 +1,8 @@
 from __future__ import annotations
 
-from typing import TYPE_CHECKING, Any, override
+import errno
+
+from typing import TYPE_CHECKING, Any, Iterable, override
 
 from ..FileContext import FileContext as Base
 
@@ -48,3 +50,8 @@ class Curl(Base):
             path = '/' + path
         cmd.append(self.uri.to_string + self._chroot(path))
         return await self.__ec.run(cmd, throw = throw, verbose = verbose)
+
+    @override
+    async def _readdir(self, path: str) -> Iterable[str]:
+        msg = f'{self.log_name}: readdir("{path}") is not implemented'
+        raise OSError(errno.ENOSYS, msg)

src/python/jw/pkg/lib/ec/Local.py

@@ -7,7 +7,7 @@ import pwd
 import sys
 
 from functools import cache
-from typing import TYPE_CHECKING, override
+from typing import TYPE_CHECKING, Iterable, override
 
 from ..base import Result, StatResult
 from ..ExecContext import ExecContext as Base
@@ -206,3 +206,7 @@ class Local(Base):
         if (not follow_symlinks) and os.path.islink(path):
             return False
         return os.path.isdir(path)
+
+    @override
+    async def _readdir(self, path: str) -> Iterable[str]:
+        return os.listdir(path)