perf(node): list a group's directories off the event loop

Every full index walked all roots on the loop, and a node with several
large roots stopped answering for seconds. Walk directories only, on the
roots' disk thread; index_sync is spawned and still answers on failure.

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

4 files changed, 78 insertions, 27 deletions

diff --git a/packages/meshbay-node/src/meshbay_node/daemon.py b/packages/meshbay-node/src/meshbay_node/daemon.py
index d6293ee..e1aac41 100644
--- a/packages/meshbay-node/src/meshbay_node/daemon.py
+++ b/packages/meshbay-node/src/meshbay_node/daemon.py
@@ -67,7 +67,11 @@ from meshbay_node.transport import (
     WEBRTC_AVAILABLE,
     Denylist,
 )
-from meshbay_node.transport.wire import index_delta_message, index_sync_message
+from meshbay_node.transport.wire import (
+    index_delta_message,
+    index_sync_message,
+    list_dirs_off_loop,
+)
 
 if QUIC_AVAILABLE:
     from meshbay_node.transport import QuicChunkServer
@@ -1452,9 +1456,11 @@ class NodeDaemon(EnrichmentMixin):
             # "nobody is listening", not a case to send in clear for.
             if peers and idx.gek:
                 hidden = self._blocklist if self._is_public(group_id) else ()
+                dirs = (None if delta is not None
+                        else await list_dirs_off_loop(indexer.roots))
                 msg = (index_delta_message(idx, delta, indexer.roots, hidden)
                        if delta is not None
-                       else index_sync_message(idx, indexer.roots, hidden))
+                       else index_sync_message(idx, indexer.roots, hidden, dirs))
                 pushed = 0
                 for session in peers:
                     try:
@@ -1488,16 +1494,18 @@ class NodeDaemon(EnrichmentMixin):
             return
         if self._blocklist.replace(hashes):
             log.info("Content blocklist: %d hashes", len(self._blocklist))
-            self._push_public_indexes()
+            await self._push_public_indexes()
 
-    def _on_blocklist_update(self, add: list, remove: list) -> None:
+    def _on_blocklist_update(self, add: list, remove: list):
+        """Returns the push it started, if any, for whoever wants to wait on it."""
         if not self._hosts_public_group():
-            return
+            return None
         if self._blocklist.apply(add, remove):
             log.info("Content blocklist updated: +%d -%d", len(add), len(remove))
-            self._push_public_indexes()
+            return spawn(self._push_public_indexes())
+        return None
 
-    def _push_public_indexes(self) -> None:
+    async def _push_public_indexes(self) -> None:
         """Resend each public group's whole index, so what the list now hides
         leaves every connected member's view, and what it released comes back."""
         if not self._webrtc:
@@ -1506,7 +1514,8 @@ class NodeDaemon(EnrichmentMixin):
             idx = indexer.index
             if not self._is_public(idx.group_id) or not idx.gek:
                 continue
-            msg = index_sync_message(idx, indexer.roots, self._blocklist)
+            dirs = await list_dirs_off_loop(indexer.roots)
+            msg = index_sync_message(idx, indexer.roots, self._blocklist, dirs)
             for session in list(self._webrtc._sessions.values()):
                 if session._group_id == idx.group_id:
                     try:
diff --git a/packages/meshbay-node/src/meshbay_node/transport/webrtc/dispatch.py b/packages/meshbay-node/src/meshbay_node/transport/webrtc/dispatch.py
index 4bf9dbb..a8b5767 100644
--- a/packages/meshbay-node/src/meshbay_node/transport/webrtc/dispatch.py
+++ b/packages/meshbay-node/src/meshbay_node/transport/webrtc/dispatch.py
@@ -18,7 +18,7 @@ MAX_PRE_PROOF_FETCHES = 4
 # records it for every type.
 SPAWNED, INLINE = True, False
 _HANDLERS = {
-    MNP.INDEX_SYNC: ("_do_index_sync", INLINE),
+    MNP.INDEX_SYNC: ("_do_index_sync", SPAWNED),
     # Spawned rather than answered inline: the reply waits for room
     # on the channel, and blocking the message loop for that would
     # stop everything else this peer is doing — including the
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 f629563..0434554 100644
--- a/packages/meshbay-node/src/meshbay_node/transport/webrtc/files.py
+++ b/packages/meshbay-node/src/meshbay_node/transport/webrtc/files.py
@@ -19,7 +19,7 @@ from meshbay_node.transport.webrtc.disk import (
     _rmdir_if_empty,
 )
 from meshbay_node.transport.webrtc.limits import CHUNK_SIZE, LEASE_GRANTED, LEASE_QUEUED
-from meshbay_node.transport.wire import index_sync_message
+from meshbay_node.transport.wire import index_sync_message, list_dirs_off_loop
 
 log = logging.getLogger("meshbay_node.transport.webrtc_server")
 
@@ -177,9 +177,21 @@ class FilesMixin:
         self._audit("dir_delete", rel)
         self._send({"type": MNP.DIR_DELETE_ACK, "v": MNP_VERSION, "dir": rel})
 
-    def _do_index_sync(self) -> None:
-        ctx = self._group_ctx()
-        self._send(index_sync_message(ctx["index"], ctx.get("roots"), self._hidden_ids()))
+    async def _do_index_sync(self) -> None:
+        try:
+            dirs = await list_dirs_off_loop(self._group_ctx().get("roots"))
+            # Read again after the walk: the entries go out as they are when the
+            # reply is sent, so no delta pushed meanwhile is older than it.
+            ctx = self._group_ctx()
+            msg = index_sync_message(ctx["index"], ctx.get("roots"), self._hidden_ids(),
+                                     dirs)
+        except Exception as e:
+            # What the dispatcher answered when this ran inline. A spawned task
+            # that fails only logs, and the client would wait out its timeout.
+            log.error("Error building index_sync: %s", e, exc_info=True)
+            self._send({"type": "error", "detail": "Request failed"})
+            return
+        self._send(msg)
 
     async def _try_serve_thumbnail(
         self, thumb_hash: str, chunk_index: int, gek: bytes | None,
diff --git a/packages/meshbay-node/src/meshbay_node/transport/wire.py b/packages/meshbay-node/src/meshbay_node/transport/wire.py
index 258edb5..77c5d62 100644
--- a/packages/meshbay-node/src/meshbay_node/transport/wire.py
+++ b/packages/meshbay-node/src/meshbay_node/transport/wire.py
@@ -27,11 +27,14 @@ message we have not yet authenticated.
 
 from __future__ import annotations
 
+import os
+from pathlib import Path
+
 from meshbay_common import MNP_VERSION
 from meshbay_common.groupbox import PURPOSE_INDEX, seal
 from meshbay_common.protocol import MNP, index_entry_wire
 
-from meshbay_node.roots import RootSet
+from meshbay_node.roots import RootSet, off_disk
 
 # A group with a deep tree can hold more directories than anyone will navigate in one
 # sitting, and the whole list rides on one message.
@@ -47,25 +50,49 @@ def list_dirs(roots: RootSet | None) -> list[str]:
     is listed too — its content is frozen, not gone, and hiding it would look exactly
     like deletion.
     """
+    return _walk_dirs(_dir_roots(roots)) if roots else []
+
+
+async def list_dirs_off_loop(roots: RootSet | None) -> list[str]:
+    """
+    `list_dirs`, on the thread that serves `roots`.
+
+    The walk is a syscall per directory over every root of the group, and it ran
+    on the event loop for each full index: on a library of several large roots
+    that was seconds in which the node answered nobody, not its members and not
+    the desktop client asking whether it was there. Found live: a tester adding a
+    sixth directory saw "Add a directory" vanish because the node missed a 3 s
+    check while it indexed the other five.
+    """
     if not roots:
         return []
+    return await off_disk(roots, _walk_dirs, _dir_roots(roots))
+
+
+def _dir_roots(roots: RootSet) -> list[tuple[str, Path, bool]]:
+    """What the walk needs from each root, read on the loop that owns them."""
+    return [(root.name, root.path, root.available) for root in roots]
+
+
+def _walk_dirs(dir_roots: list[tuple[str, Path, bool]]) -> list[str]:
+    """Blocking. Directories only: `os.walk` reads each one once and never
+    stats a file, which `rglob("*")` and an `is_dir()` per entry did."""
     out: list[str] = []
-    for root in roots:
-        out.append(root.name)
-        if not root.available:
-            continue
-        try:
-            for path in sorted(root.path.rglob("*")):
-                if path.is_dir() and not path.name.startswith("."):
-                    rel = path.relative_to(root.path)
-                    if not any(part.startswith(".") for part in rel.parts):
-                        out.append(f"{root.name}/{rel.as_posix()}")
-        except OSError:
+    for name, path, available in dir_roots:
+        out.append(name)
+        if not available:
             continue
+        for top, subdirs, _files in os.walk(path):
+            # Pruned in place: nothing under a hidden directory is listed either.
+            subdirs[:] = [d for d in subdirs if not d.startswith(".")]
+            rel = Path(top).relative_to(path)
+            for d in subdirs:
+                out.append(f"{name}/{(rel / d).as_posix()}")
     return sorted(out)[:MAX_DIRS]
 
 
-def index_sync_message(index, roots: RootSet | None, hidden=()) -> dict:
+def index_sync_message(index, roots: RootSet | None, hidden=(),
+                       dirs: list[str] | None = None) -> dict:
     """
     The full `index_sync` message for one group.
 
@@ -76,11 +103,14 @@ def index_sync_message(index, roots: RootSet | None, hidden=()) -> dict:
 
     `hidden` is the content blocklist in a public group (`meshbay_node.blocklist`):
     those entries are not sent at all.
+
+    `dirs` is `list_dirs_off_loop(roots)`, awaited by a caller on the event loop;
+    left out, the walk runs here, where the caller is.
     """
     payload = {
         "version": index.version,
         "entries": [index_entry_wire(e) for e in index.entries if e.id not in hidden],
-        "dirs": list_dirs(roots),
+        "dirs": list_dirs(roots) if dirs is None else dirs,
         "roots": roots.describe() if roots else [],
     }
     return {