fix: make NodeReplaceManager.register() idempotent

When the same (old_node_id, new_node_id) pair is registered more than
once in the same process, the duplicate is now silently ignored (with a
debug log). Previously every call appended a new entry, so reloading a
custom node — e.g. via ComfyUI-Manager hot-reload — would accumulate
stale duplicate replacements that surfaced through GET /node_replacements.

Multiple distinct alternatives for the same old_node_id (different
new_node_ids) are still preserved, matching the existing 'list of
alternatives' design used by apply_replacements().

Adds unit tests in tests-unit/app_test/node_replace_manager_test.py
covering normal registration, multi-alternative support, dedupe, and
first-write-wins ordering.

Co-authored-by: Amp <amp@ampcode.com>
Amp-Thread-ID: https://ampcode.com/threads/T-019dd37c-4751-72ef-9927-3182b5825db0

app/node_replace_manager.py

@@ -1,5 +1,7 @@
 from __future__ import annotations
 
+import logging
+
 from aiohttp import web
 
 from typing import TYPE_CHECKING, TypedDict
@@ -31,8 +33,22 @@ class NodeReplaceManager:
         self._replacements: dict[str, list[NodeReplace]] = {}
 
     def register(self, node_replace: NodeReplace):
-        """Register a node replacement mapping."""
-        self._replacements.setdefault(node_replace.old_node_id, []).append(node_replace)
+        """Register a node replacement mapping.
+
+        Idempotent: if a replacement with the same (old_node_id, new_node_id)
+        is already registered, the duplicate is ignored. This prevents stale
+        entries from accumulating when custom nodes are reloaded in the same
+        process (e.g. via ComfyUI-Manager).
+        """
+        existing = self._replacements.setdefault(node_replace.old_node_id, [])
+        for entry in existing:
+            if entry.new_node_id == node_replace.new_node_id:
+                logging.debug(
+                    "Node replacement %s -> %s already registered, ignoring duplicate.",
+                    node_replace.old_node_id, node_replace.new_node_id,
+                )
+                return
+        existing.append(node_replace)
 
     def get_replacement(self, old_node_id: str) -> list[NodeReplace] | None:
         """Get replacements for an old node ID."""

tests-unit/app_test/node_replace_manager_test.py

@@ -0,0 +1,76 @@
+"""Tests for NodeReplaceManager registration behavior."""
+import sys
+import types
+
+# Stub `nodes` to avoid the heavy torch + ComfyUI import chain — register()
+# only touches its own dict, so it doesn't actually need NODE_CLASS_MAPPINGS.
+if "nodes" not in sys.modules:
+    _fake_nodes = types.ModuleType("nodes")
+    _fake_nodes.NODE_CLASS_MAPPINGS = {}
+    sys.modules["nodes"] = _fake_nodes
+
+from app.node_replace_manager import NodeReplaceManager  # noqa: E402
+
+
+class FakeNodeReplace:
+    """Lightweight stand-in for comfy_api.latest._io.NodeReplace."""
+    def __init__(self, new_node_id, old_node_id, old_widget_ids=None,
+                 input_mapping=None, output_mapping=None):
+        self.new_node_id = new_node_id
+        self.old_node_id = old_node_id
+        self.old_widget_ids = old_widget_ids
+        self.input_mapping = input_mapping
+        self.output_mapping = output_mapping
+
+
+def test_register_adds_replacement():
+    manager = NodeReplaceManager()
+    manager.register(FakeNodeReplace(new_node_id="NewNode", old_node_id="OldNode"))
+    assert manager.has_replacement("OldNode")
+    assert len(manager.get_replacement("OldNode")) == 1
+
+
+def test_register_allows_multiple_alternatives_for_same_old_node():
+    """Different new_node_ids for the same old_node_id should all be kept."""
+    manager = NodeReplaceManager()
+    manager.register(FakeNodeReplace(new_node_id="AltA", old_node_id="OldNode"))
+    manager.register(FakeNodeReplace(new_node_id="AltB", old_node_id="OldNode"))
+    replacements = manager.get_replacement("OldNode")
+    assert len(replacements) == 2
+    assert {r.new_node_id for r in replacements} == {"AltA", "AltB"}
+
+
+def test_register_is_idempotent_for_duplicate_pair():
+    """Re-registering the same (old_node_id, new_node_id) should be a no-op."""
+    manager = NodeReplaceManager()
+    manager.register(FakeNodeReplace(new_node_id="NewNode", old_node_id="OldNode"))
+    manager.register(FakeNodeReplace(new_node_id="NewNode", old_node_id="OldNode"))
+    manager.register(FakeNodeReplace(new_node_id="NewNode", old_node_id="OldNode"))
+    assert len(manager.get_replacement("OldNode")) == 1
+
+
+def test_register_idempotent_preserves_first_registration():
+    """First registration wins; later duplicates with different mappings are ignored."""
+    manager = NodeReplaceManager()
+    first = FakeNodeReplace(
+        new_node_id="NewNode", old_node_id="OldNode",
+        input_mapping=[{"new_id": "a", "old_id": "x"}],
+    )
+    second = FakeNodeReplace(
+        new_node_id="NewNode", old_node_id="OldNode",
+        input_mapping=[{"new_id": "b", "old_id": "y"}],
+    )
+    manager.register(first)
+    manager.register(second)
+    replacements = manager.get_replacement("OldNode")
+    assert len(replacements) == 1
+    assert replacements[0] is first
+
+
+def test_register_dedupe_does_not_affect_other_old_nodes():
+    manager = NodeReplaceManager()
+    manager.register(FakeNodeReplace(new_node_id="NewA", old_node_id="OldA"))
+    manager.register(FakeNodeReplace(new_node_id="NewA", old_node_id="OldA"))
+    manager.register(FakeNodeReplace(new_node_id="NewB", old_node_id="OldB"))
+    assert len(manager.get_replacement("OldA")) == 1
+    assert len(manager.get_replacement("OldB")) == 1