2 files changed, 62 insertions, 1 deletions

diff --git a/packages/meshbay-cli/src/meshbay_cli/client/tree.py b/packages/meshbay-cli/src/meshbay_cli/client/tree.py
index 6e537ef..dd3acc8 100644
--- a/packages/meshbay-cli/src/meshbay_cli/client/tree.py
+++ b/packages/meshbay-cli/src/meshbay_cli/client/tree.py
@@ -57,6 +57,39 @@ class Tree:
         dirs |= set(roots)
         return cls(roots, dirs, files)
 
+    def apply_delta(self, delta: dict) -> bool:
+        """
+        Bring the tree up to an `index_delta`, in place. True when the delta
+        changed what the tree holds — a file added or removed, a root's state —
+        rather than only the fields of files already there.
+
+        A delta carries no `dirs`, so an empty folder made elsewhere is not in
+        it: a structural change is where the caller asks for the whole index
+        again, once. The common delta is enrichment filling in a file's fields,
+        about one a second while a library is being enriched, and asking for
+        the whole index on each of those took the download's own event loop:
+        67 full indexes in the 80 s of one download.
+        """
+        updates = {e["id"]: e for e in delta.get("updates", [])}
+        gone = set(delta.get("deletions", []))
+        for parent, entries in self.files.items():
+            if gone or any(e["id"] in updates for e in entries):
+                self.files[parent] = [updates.get(e["id"], e) for e in entries
+                                      if e["id"] not in gone]
+        known = {e["id"] for entries in self.files.values() for e in entries}
+        added = [e for e in delta.get("additions", []) if e["id"] not in known]
+        for e in added:
+            self.files.setdefault(e["path"], []).append(e)
+            parts = e["path"].split("/")
+            for i in range(1, len(parts) + 1):
+                self.dirs.add("/".join(parts[:i]))
+        roots = {r["name"]: r for r in delta.get("roots", [])}
+        moved_roots = bool(roots) and roots != self.roots
+        if moved_roots:
+            self.roots = roots
+            self.dirs |= set(roots)
+        return bool(gone or added or moved_roots)
+
     def root_available(self, path: str) -> bool:
         root = self.roots.get(path.split("/", 1)[0])
         return bool(root.get("available", True)) if root else True
diff --git a/packages/meshbay-cli/src/meshbay_cli/tui/screens.py b/packages/meshbay-cli/src/meshbay_cli/tui/screens.py
index 39b5df3..b6fd347 100644
--- a/packages/meshbay-cli/src/meshbay_cli/tui/screens.py
+++ b/packages/meshbay-cli/src/meshbay_cli/tui/screens.py
@@ -41,6 +41,9 @@ from .panes import LocalPane, RemotePane
 from .widgets import Choice, TransferStrip
 
 PER_GROUP = 2
+# A burst of index updates that added or removed files is answered by one full
+# index, this long after the last of them.
+REFRESH_AFTER_DELTA_S = 2.0
 
 
 class SignInScreen(Screen):
@@ -118,6 +121,7 @@ class MainScreen(Screen):
         self._trees: dict[str, Tree] = {}
         self._gates: dict[str, asyncio.Semaphore] = {}
         self._watching: set[str] = set()
+        self._refreshes: dict[str, asyncio.TimerHandle] = {}
 
     def compose(self) -> ComposeResult:
         with Horizontal():
@@ -150,12 +154,36 @@ class MainScreen(Screen):
             self._trees[group["id"]] = Tree.from_index(await session.index())
             if group["id"] not in self._watching:
                 self._watching.add(group["id"])
-                session.ch.on_push("index_delta", lambda _msg, g=group: self._changed(g))
+                session.ch.on_push(
+                    "index_delta", lambda msg, g=group, s=session: self._delta(g, s, msg))
         return self._trees[group["id"]]
 
     def forget_tree(self, group: dict) -> None:
         self._trees.pop(group["id"], None)
 
+    def _delta(self, group: dict, session, msg: dict) -> None:
+        """A pushed index update, applied to the tree in place. Only one that
+        adds or removes something is drawn, and asks for the whole index — once
+        for a burst, not once per message."""
+        tree = self._trees.get(group["id"])
+        if tree is None:
+            return   # the next look asks for the whole index anyway
+        try:
+            structural = tree.apply_delta(session.open_delta(msg))
+        except CliError:
+            structural = True
+        if not structural:
+            return
+        pending = self._refreshes.pop(group["id"], None)
+        if pending is not None:
+            pending.cancel()
+        self._refreshes[group["id"]] = asyncio.get_running_loop().call_later(
+            REFRESH_AFTER_DELTA_S, self._refreshed, group)
+
+    def _refreshed(self, group: dict) -> None:
+        self._refreshes.pop(group["id"], None)
+        self._changed(group)
+
     def _changed(self, group: dict) -> None:
         """Something changed in the group: the index is asked for again, and the
         pane redrawn if it is showing that group."""