fix(node): index, serve and write files past Windows' MAX_PATHHEADmain

With the system's default setting (LongPathsEnabled off) every call given
a plain path of 260 characters or more refuses it, so a deep library was
partly invisible: the walk could not list such a directory and its files
never reached the members.

The node now hands each call that touches a group's disk the extended
form (paths.long_path), and keeps the plain path in the index, the hash
cache and the log. A directory is listed under its long form and its
entries named from the plain one (indexer.walk_files, wire._walk_dirs).
Covered: the walk, stats and hashing, reconcile and the watcher, the
folder list members see, serving over WebRTC and QUIC, deletion, uploads
and their recovery, folder creation and removal, audio tags and the
cover beside a track, photos, and a show's episode numbering. ffmpeg
extends a long path itself and keeps the plain one.

long_path now normalises before prefixing (the extended form skips the
system's normalisation) and starts at 248 characters, where creating a
directory is already refused.

test_long_paths.py runs with the setting off: 15 of its 17 tests fail
without the change. Checked by hand in the installed app with files at
312 to 380 characters.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

3 files changed, 40 insertions, 16 deletions

diff --git a/packages/meshbay-node/src/meshbay_node/transport/webrtc/disk.py b/packages/meshbay-node/src/meshbay_node/transport/webrtc/disk.py
index e298942..386b81f 100644
--- a/packages/meshbay-node/src/meshbay_node/transport/webrtc/disk.py
+++ b/packages/meshbay-node/src/meshbay_node/transport/webrtc/disk.py
@@ -1,8 +1,15 @@
-"""Blocking disk work the session hands to `off_disk`."""
+"""
+Blocking disk work the session hands to `off_disk`.
 
+Every call takes the path's long form (`long_path`): a file past Windows'
+MAX_PATH is indexed, so it is served, deleted and written beside like any other.
+"""
+
+import os
 import shutil
 from pathlib import Path
 
+from meshbay_common.paths import long_path
 from meshbay_common.protocol import file_chunk_wire
 
 from meshbay_node.roots import ROOT_NOT_SERVED, RootSet, entry_abs_path
@@ -22,7 +29,7 @@ def _locate(roots: RootSet, entry) -> tuple[Path | None, str | None]:
     path = entry_abs_path(roots, entry)
     if path is None:
         return None, ROOT_NOT_SERVED
-    if not path.exists():
+    if not os.path.exists(long_path(path)):
         return None, "File not on disk"
     return path, None
 
@@ -37,15 +44,16 @@ def _mkdir_if_absent(target: Path) -> str | None:
     `mkdir` would raise where a refusal was meant. Blocking; called through
     `off_disk`.
     """
-    if target.exists():
+    if os.path.exists(long_path(target)):
         return "Already exists"
-    target.mkdir(parents=False)
+    os.mkdir(long_path(target))
     return None
 
 
 def _is_empty_dir(target: Path) -> bool:
     """Blocking; called through `off_disk`."""
-    return not any(target.iterdir())
+    with os.scandir(long_path(target)) as listing:
+        return not any(listing)
 
 
 def _rmdir_if_empty(target: Path) -> bool:
@@ -57,9 +65,10 @@ def _rmdir_if_empty(target: Path) -> bool:
     operator's browser, and a file can land in between. Two awaits here would
     reopen the same window one size smaller. Blocking; called through `off_disk`.
     """
-    if any(target.iterdir()):
-        return False
-    target.rmdir()
+    with os.scandir(long_path(target)) as listing:
+        if any(listing):
+            return False
+    os.rmdir(long_path(target))
     return True
 
 
@@ -71,7 +80,7 @@ def _read_and_encrypt(
     file_id: str = "",
 ) -> dict:
     """Read one chunk off disk and encrypt it. Blocking; called through `off_disk`."""
-    with open(file_path, "rb") as f:
+    with open(long_path(file_path), "rb") as f:
         f.seek(chunk_index * CHUNK_SIZE)
         plaintext = f.read(CHUNK_SIZE)
     return file_chunk_wire(gek, plaintext, chunk_index, file_hash, file_id)
@@ -80,10 +89,24 @@ def _read_and_encrypt(
 def _free_bytes(directory: Path) -> int:
     """Space left on the filesystem holding `directory`. Blocking; called
     through `off_disk`, since a `statvfs` wakes a sleeping disk like any stat."""
-    return shutil.disk_usage(directory).free
+    return shutil.disk_usage(long_path(directory)).free
 
 
 def _append_chunk(tmp_path: Path, chunk_bytes: bytes, first: bool) -> None:
     """Add one chunk to a partial upload. Blocking; called through `off_disk`."""
-    with open(tmp_path, "wb" if first else "ab") as f:
+    with open(long_path(tmp_path), "wb" if first else "ab") as f:
         f.write(chunk_bytes)
+
+
+def _unlink(path: Path, missing_ok: bool = False) -> None:
+    """Remove one file. Blocking; called through `off_disk`."""
+    try:
+        os.unlink(long_path(path))
+    except FileNotFoundError:
+        if not missing_ok:
+            raise
+
+
+def _exists(path: Path) -> bool:
+    """Blocking; called through `off_disk`."""
+    return os.path.exists(long_path(path))
diff --git a/packages/meshbay-node/src/meshbay_node/transport/webrtc/files.py b/packages/meshbay-node/src/meshbay_node/transport/webrtc/files.py
index eafdaed..9c5fab5 100644
--- a/packages/meshbay-node/src/meshbay_node/transport/webrtc/files.py
+++ b/packages/meshbay-node/src/meshbay_node/transport/webrtc/files.py
@@ -17,6 +17,7 @@ from meshbay_node.transport.webrtc.disk import (
     _mkdir_if_absent,
     _read_and_encrypt,
     _rmdir_if_empty,
+    _unlink,
 )
 from meshbay_node.transport.webrtc.limits import CHUNK_SIZE, LEASE_GRANTED, LEASE_QUEUED
 from meshbay_node.transport.wire import index_sync_message, list_dirs_off_loop
@@ -439,7 +440,7 @@ class FilesMixin:
             self._send({"type": "error", "detail": ROOT_NOT_SERVED})
             return
         if file_path is not None:
-            await off_disk(ctx["roots"], file_path.unlink)
+            await off_disk(ctx["roots"], _unlink, file_path)
             log.info("File deleted: %s", entry.name)
             self._audit("file_delete", entry.name)
 
diff --git a/packages/meshbay-node/src/meshbay_node/transport/webrtc/upload_handlers.py b/packages/meshbay-node/src/meshbay_node/transport/webrtc/upload_handlers.py
index c052703..0d5bb0e 100644
--- a/packages/meshbay-node/src/meshbay_node/transport/webrtc/upload_handlers.py
+++ b/packages/meshbay-node/src/meshbay_node/transport/webrtc/upload_handlers.py
@@ -17,7 +17,7 @@ from meshbay_node.roots import (
     publish_upload,
     shell_active,
 )
-from meshbay_node.transport.webrtc.disk import _append_chunk, _free_bytes
+from meshbay_node.transport.webrtc.disk import _append_chunk, _exists, _free_bytes, _unlink
 from meshbay_node.transport.webrtc.limits import LEASE_GRANTED, LEASE_NONE, LEASE_QUEUED
 
 log = logging.getLogger("meshbay_node.transport.webrtc_server")
@@ -365,7 +365,7 @@ class UploadMixin:
         if chunk_index == 0:
             # Backstop: _free_name already guarantees this, and it stays because
             # it asserts the invariant where the write happens.
-            if await off_disk(roots, final_path.exists):
+            if await off_disk(roots, _exists, final_path):
                 _refuse("File already exists", "already_exists")
                 return
             # Asked once, before the first byte, from the size the client
@@ -396,7 +396,7 @@ class UploadMixin:
 
         if state.bytes + len(chunk_bytes) > self._max_upload_bytes():
             uploads.drop(user_id, rel_dir, filename)
-            await off_disk(roots, tmp_path.unlink, True)
+            await off_disk(roots, _unlink, tmp_path, True)
             _refuse("Upload exceeds size limit", "too_large")
             return
 
@@ -410,7 +410,7 @@ class UploadMixin:
             # space that ran out. The client starts over from zero, which is
             # what it would have to do for a resume against a full disk anyway.
             uploads.drop(user_id, rel_dir, filename)
-            await off_disk(roots, tmp_path.unlink, True)
+            await off_disk(roots, _unlink, tmp_path, True)
             log.warning("Upload refused: the disk holding %s is full", rel_dir)
             self._audit("upload_refused", "disk_full")
             _refuse("The node's disk is full", "disk_full")