Support uninstalled / missing nodes

Previously the index was built only from the live registry, so a custom node
that wasn't installed (a red "missing" node in a downloaded workflow) was
invisible — the main point of the tool. Now:

- Backend: utfcn_core split into build_context / build_index / match. build_index
  also emits curated candidates for uninstalled source types (curated-only), and
  a new POST /utfcn/match matches missing nodes by their serialized signature
  against installed core/other-pack nodes.
- Frontend: nodeType() reads a missing placeholder's last_serialization.type;
  matchMissing() feeds serialized slots to /utfcn/match and merges the results;
  the right-click item moved to a canvas-level getNodeMenuOptions patch so it
  reaches missing placeholders too. Bulk dialog labels them "not installed".

Replace a missing node with core without installing its pack. Links are rewired
losslessly; widget values can't be carried for a node whose def is absent.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

__init__.py

@@ -13,7 +13,9 @@ All of that is frontend behaviour (see web/utfcn.js).  This backend only serves
 the *analysis*: it has the live node registry, so it computes — accurately, from
 real INPUT_TYPES / RETURN_TYPES — which custom nodes have safe equivalents.
 
-  GET /utfcn/scan[?refresh=1]   -> { sources, candidates, stats }
+  GET  /utfcn/scan[?refresh=1]   -> { sources, candidates, stats }
+  POST /utfcn/match  {nodes:[{type,inputs,outputs,output_names}]} -> { candidates }
+                                   (for UNINSTALLED / missing nodes in a workflow)
 
 Curated overrides live in mappings.json (shipped) and user_mappings.json (yours).
 """
@@ -28,15 +30,23 @@ from . import utfcn_core
 VERSION = "1.0.0"
 _DIR = os.path.dirname(os.path.realpath(__file__))
 
-# The scan walks the whole registry, so we cache it and only rebuild on demand.
+# Snapshotting the registry is the expensive part, so we cache the context and
+# the derived scan index, rebuilding only on ?refresh=1.
+_CTX_CACHE = None
 _INDEX_CACHE = None
 
 
+def _get_ctx(refresh=False):
+    global _CTX_CACHE
+    if refresh or _CTX_CACHE is None:
+        _CTX_CACHE = utfcn_core.build_context(utfcn_core.load_rules(_DIR))
+    return _CTX_CACHE
+
+
 def _get_index(refresh=False):
     global _INDEX_CACHE
     if refresh or _INDEX_CACHE is None:
-        rules = utfcn_core.load_rules(_DIR)
-        _INDEX_CACHE = utfcn_core.build_index(rules)
+        _INDEX_CACHE = utfcn_core.build_index(_get_ctx(refresh))
     return _INDEX_CACHE
 
 
@@ -54,6 +64,20 @@ async def utfcn_scan(request):
         return web.json_response({"sources": {}, "candidates": {}, "stats": {}, "error": str(e)}, status=500)
 
 
+@routes.post("/utfcn/match")
+async def utfcn_match(request):
+    """Match uninstalled/missing nodes by their serialized signature."""
+    try:
+        data = await request.json()
+    except Exception:
+        return web.json_response({"candidates": {}, "error": "invalid json"}, status=400)
+    try:
+        return web.json_response({"candidates": utfcn_core.match(_get_ctx(), data.get("nodes") or [])})
+    except Exception as e:
+        print(f"[UTFCN] match failed: {e}")
+        return web.json_response({"candidates": {}, "error": str(e)}, status=500)
+
+
 WEB_DIRECTORY = "./web"
 NODE_CLASS_MAPPINGS = {}
 NODE_DISPLAY_NAME_MAPPINGS = {}