Skip held-subtree scans when no subtrees are held

evidence/sidebar-layout-invalidation-20261006/README.md

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+# Skip held-subtree traversal when none is held
+
+The sidebar profile exposed complete committed-map ancestry scans in
+`Compositor._arrange_root` and `deferred_regions` even with no held roots.
+Screen also scanned callback ancestry and retained layout members against an
+empty root set. The existing owners now derive the empty result immediately.
+Nonempty roots use the original matching, damage and callback rules. No map,
+cache, mask, queue or size-dependent measurement contract changed.
+
+Before/after AST uses the existing audit Package parser. Native production249,
+tests467; dependency Toad production288/tests403/tools40: no parse omissions.
+Lexical sites do not resolve arbitrary external dynamic overrides. Original
+Screen/Compositor/Widget owners and Toad viewport/anchor hooks were read.
+
+One matched source App run used Toad437e/Core574 with the changed native source,
+508 widgets/10 tabs, no provider. It exited0 with empty stderr. Ancestry visits
+fell2746→1242 (left) and3230→1166 (right); empty deferred-region work fell from
+~0.8–1.3ms to~0.001ms. Overall medians41.8/47.4ms do not establish an improvement
+over the original43.8/41ms. This is a small removed cost, not solved latency.
+
+The original six-check batch produced5PASS and one preserved failure: its
+callback test expected the Screen to wait inside an admitted async callback.
+The existing control now asserts the actual sender task, preserved callback
+order and completion inside a later batch after original publication admission.
+That changed control alone passed1/.26s; the other five were not repeated.
+MessagePump.call_after_refresh and merged#75 own this lifetime. No production
+callback rule changed. The five existing controls cover actual batches, held
+subtree geometry/hits/callbacks, inline publication and translucent backdrops.
+
+RESULT.json references the exact original/new profiles and App logs. No
+installed pin, public runtime or frozen original evidence changed. The App
+fixture cleaned its authored roots; no child operation is left running.

evidence/sidebar-layout-invalidation-20261006/RESULT.json

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+{
+  "scope": "Existing source App sidebar width changes; no installed/live speed claim",
+  "app_exit": 0,
+  "app": {
+    "boundary": "completed headless _display; not terminal pixels",
+    "tabs": 10,
+    "pointer": true,
+    "active_widgets": 508,
+    "toggle_first_paint": {
+      "#channels-sidebar": {
+        "median_ms": 41.8,
+        "p95_ms": 63.7,
+        "max_ms": 166.3
+      },
+      "#thread-sidebar": {
+        "median_ms": 47.4,
+        "p95_ms": 52.5,
+        "max_ms": 91.5
+      }
+    }
+  },
+  "profiles": {
+    "channels": {
+      "before": {
+        "_arrange_root": {
+          "calls": 1,
+          "cumulative_ms": 40.386162000000006
+        },
+        "deferred_regions": {
+          "calls": 1,
+          "cumulative_ms": 1.3299400000000001
+        },
+        "walk_ancestors": {
+          "calls": 2746,
+          "cumulative_ms": 3.615679
+        }
+      },
+      "after": {
+        "_arrange_root": {
+          "calls": 1,
+          "cumulative_ms": 38.969518
+        },
+        "deferred_regions": {
+          "calls": 1,
+          "cumulative_ms": 0.001002
+        },
+        "walk_ancestors": {
+          "calls": 1242,
+          "cumulative_ms": 1.8329140000000002
+        }
+      }
+    },
+    "thread": {
+      "before": {
+        "_arrange_root": {
+          "calls": 1,
+          "cumulative_ms": 17.421249
+        },
+        "deferred_regions": {
+          "calls": 1,
+          "cumulative_ms": 0.7913190000000001
+        },
+        "walk_ancestors": {
+          "calls": 3230,
+          "cumulative_ms": 3.083367
+        }
+      },
+      "after": {
+        "_arrange_root": {
+          "calls": 1,
+          "cumulative_ms": 17.359883
+        },
+        "deferred_regions": {
+          "calls": 1,
+          "cumulative_ms": 0.000921
+        },
+        "walk_ancestors": {
+          "calls": 1166,
+          "cumulative_ms": 1.335096
+        }
+      }
+    }
+  },
+  "raw_sha256": {
+    "/home/ts/.cache/agent-scratch/native-sidebar-invalidation-20261006/app.stdout.log": "e931e3a60e42ec6a3c7bbda9862412551f3e9477f3a3aeb6ecbe91179100518d",
+    "/home/ts/.cache/agent-scratch/native-sidebar-invalidation-20261006/app.stderr.log": "e3b0c44298fc1c149afbf4c8996fb92427ae41e4649b934ca495991b7852b855",
+    "/home/ts/.cache/agent-scratch/native-sidebar-invalidation-20261006/toggle-channels.pstats": "d165e9aec8ea0fd26d8d3cdb0fccdf19924599f64de4039bf26685137205a03e",
+    "/home/ts/.cache/agent-scratch/native-sidebar-invalidation-20261006/toggle-thread.pstats": "a94dbded3baa0b5ce704230d524e1c7f93ac11733ecc82964ee911f3614d9288",
+    "/home/ts/.cache/agent-scratch/tab-sidebar-native-app-20261006/toggle-channels.pstats": "62677e584d201d63342784575c10fa63a2017d6ce85d3d16d8811302c1c20bf0",
+    "/home/ts/.cache/agent-scratch/tab-sidebar-native-app-20261006/toggle-thread.pstats": "631271560a14978c886afbd94602dd885eb25489c5ad06e9196b868dafac6ce1"
+  },
+  "publication_controls": "Original batch5PASS/1 preserved pre75 Screen-custody failure; migrated existing sender-completion control alonePASS. Other five not repeated.",
+  "remaining": "No reliable toggle latency improvement. Width-dependent measurement and paint remain required. The original profiles also include Core MroDispatch handler discovery; no Core edit.",
+  "sender_control_sha256": "364fae48cbe8f4ef8e995f8fb3224d43792e784eb9919ceefea2fe0106918edf"
+}