refactor: extract _track helper for available_channels sync in apply_writes

Replace 5 repeated inline blocks that sync available_channels with
a local _track() helper that checks is_available() and updates the
set, returning the availability bool for callers that also need to
update updated_channels.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

libs/langgraph/langgraph/pregel/_algo.py

@@ -282,6 +282,18 @@ def apply_writes(
             None,
         )
 
+    # Sync available_channels with channel's actual availability state.
+    # Returns True if the channel is available (for callers that also need
+    # to update updated_channels).
+    def _track(chan: str) -> bool:
+        avail = channels[chan].is_available()
+        if available_channels is not None:
+            if avail:
+                available_channels.add(chan)
+            else:
+                available_channels.discard(chan)
+        return avail
+
     # Consume all channels that were read
     for chan in {
         chan
@@ -291,11 +303,7 @@ def apply_writes(
     }:
         if channels[chan].consume() and next_version is not None:
             checkpoint["channel_versions"][chan] = next_version
-        if available_channels is not None:
-            if channels[chan].is_available():
-                available_channels.add(chan)
-            else:
-                available_channels.discard(chan)
+        _track(chan)
 
     # Group writes by channel
     pending_writes_by_channel: dict[str, list[Any]] = defaultdict(list)
@@ -325,17 +333,10 @@ def apply_writes(
             if channels[chan].update(vals) and next_version is not None:
                 checkpoint["channel_versions"][chan] = next_version
                 # unavailable channels can't trigger tasks, so don't add them
-                if channels[chan].is_available():
+                if _track(chan):
                     updated_channels.add(chan)
-                    if available_channels is not None:
-                        available_channels.add(chan)
-                elif available_channels is not None:
-                    available_channels.discard(chan)
-            elif available_channels is not None:
-                if channels[chan].is_available():
-                    available_channels.add(chan)
-                else:
-                    available_channels.discard(chan)
+            else:
+                _track(chan)
 
     # Channels that weren't updated in this step are notified of a new step
     if bump_step:
@@ -352,10 +353,8 @@ def apply_writes(
             if channels[chan].update(EMPTY_SEQ) and next_version is not None:
                 checkpoint["channel_versions"][chan] = next_version
                 # unavailable channels can't trigger tasks, so don't add them
-                if channels[chan].is_available():
+                if _track(chan):
                     updated_channels.add(chan)
-                elif available_channels is not None:
-                    available_channels.discard(chan)
 
     # If this is (tentatively) the last superstep, notify all channels of finish
     if bump_step and updated_channels.isdisjoint(trigger_to_nodes):
@@ -363,17 +362,10 @@ def apply_writes(
             if channels[chan].finish() and next_version is not None:
                 checkpoint["channel_versions"][chan] = next_version
                 # unavailable channels can't trigger tasks, so don't add them
-                if channels[chan].is_available():
+                if _track(chan):
                     updated_channels.add(chan)
-                    if available_channels is not None:
-                        available_channels.add(chan)
-                elif available_channels is not None:
-                    available_channels.discard(chan)
-            elif available_channels is not None:
-                if channels[chan].is_available():
-                    available_channels.add(chan)
-                else:
-                    available_channels.discard(chan)
+            else:
+                _track(chan)
 
     # Return managed values writes to be applied externally
     return updated_channels

libs/langgraph/langgraph/pregel/_loop.py

@@ -198,7 +198,6 @@ class PregelLoop:
     _migrate_checkpoint: Callable[[Checkpoint], None] | None
     submit: Submit
     channels: Mapping[str, BaseChannel]
-    _has_untracked_channels: bool
     _available_channels: set[str]
     # Futures from `checkpointer.put_writes` calls that produced delta-channel
     # writes. `_checkpointer_put_after_previous` drains this list (swap to a