Avoid allocating empty collections in message handler lookup

evidence/handler-allocation-20261007/README.md

@@ -0,0 +1,15 @@
+# Handler lookup allocations
+
+The existing metaclass already collects decorated declarations and parses selectors. No declaration registry or event cache is needed. Named handlers must remain live: an awaited decorated handler can replace the named handler that follows it. C3 order, instance binding, selectors and bubbling remain runtime work.
+
+The original lookup constructed an empty list on every missing decorated-handler match, including each message ancestor in each decorated class table. It also allocated a duplicate-tracking set even when no decorated candidate existed. Lookup now uses the immutable empty tuple on a miss and creates its set at the first decorated candidate. Existing declaration lists and post-yield duplicate accounting are unchanged.
+
+The existing refactor-audit Package parsed 250 production modules without omissions. `_get_dispatch_methods` is used by `_on_message` and idle delivery; both use the same changed implementation. No other declaration-table writer was found beyond `_MessagePumpMeta`; dynamic class mappings and decorated lists remain live.
+
+Fourteen affected original decorator/message checks passed in 2.18 seconds, including inherited duplicate suppression, C3/private precedence, selector matching and live replacement during awaited dispatch.
+
+One original channel App check passed: 160 authored private messages, 20 arrivals, focused history paging; sequence113 to73, 88 mounted rows, no App error, empty stderr. Installed Toad/Core came from viewer-cut-and-header-delivery-20261007; only native source was supplied. The installed message-pump diff consists exactly of these allocation changes. No provider, installed-package write or public operation. Original fixture teardown joined its private work; individual child birth identities were not collected.
+
+Raw result/profile/logs: /home/ts/.cache/agent-scratch/native-handler-allocation-20261007. Previous profile: /home/ts/.cache/agent-scratch/installed-viewer-cut-header-20261007/ui.pstats.
+
+Profiling recorded229908→214884 lookup calls, own time.9755→.9351s and inclusive1.5684→1.4606s. Own time per invocation4.24→4.35microseconds did not improve. Heartbeatp95 went46.13→35.11ms, maximum182.39→227.40ms; arrangement workload and final scroll position differed. These runs do not establish a reliable responsiveness or overall speed gain. Layout remains substantial required work.

evidence/handler-allocation-20261007/app-result.json

@@ -0,0 +1,15 @@
+{
+  "main_loop_samples": 2387,
+  "median_ms": 6.166572915390134,
+  "p95_ms": 35.106428898870945,
+  "max_ms": 227.4037009337917,
+  "gaps_above_50ms": 61,
+  "mounted_rows": 88,
+  "oldest_sequence": 73,
+  "app_error": null,
+  "profiling": true,
+  "initial_scroll": 215,
+  "final_scroll": 803,
+  "initial_oldest": 113,
+  "older_page": 73
+}

src/textual/message_pump.py

@@ -836,7 +836,7 @@ def _get_dispatch_methods(
         """
         from textual.widget import Widget
 
-        methods_dispatched: set[Callable] = set()
+        methods_dispatched: set[Callable] | None = None
         message_types = message.__class__.__mro__
         message_mro: list[type[Message]] | None = None
         private_method_name = f"_{method_name}"
@@ -856,9 +856,11 @@ def _get_dispatch_methods(
                         _type for _type in message_types if issubclass(_type, Message)
                     ]
                 for message_class in message_mro:
-                    handlers = decorated_handlers.get(message_class, [])
+                    handlers = decorated_handlers.get(message_class, ())
 
                     for method, selectors in handlers:
+                        if methods_dispatched is None:
+                            methods_dispatched = set()
                         if method in methods_dispatched:
                             continue
                         if not selectors: