diff --git a/.github/workflows/dart.yml b/.github/workflows/dart.yml
index 24d0b31d60..7ae1580a16 100644
--- a/.github/workflows/dart.yml
+++ b/.github/workflows/dart.yml
@@ -1,4 +1,4 @@
-# Created with package:mono_repo v6.6.2
+# Created with package:mono_repo v6.6.3
 name: Dart CI
 on:
   push:
@@ -36,7 +36,7 @@ jobs:
         name: Checkout repository
         uses: actions/checkout@93ea575cb5d8a053eaa0ac8fa3b40d7e05a33cc8
       - name: mono_repo self validate
-        run: dart pub global activate mono_repo 6.6.2
+        run: dart pub global activate mono_repo 6.6.3
       - name: mono_repo self validate
         run: dart pub global run mono_repo generate --validate
   job_002:
@@ -1680,6 +1680,81 @@ jobs:
       - job_007
       - job_008
   job_045:
+    name: "leak_check; linux; Dart dev; PKG: build_runner_core; `../tool/leak_check.sh`"
+    runs-on: ubuntu-latest
+    steps:
+      - name: Cache Pub hosted dependencies
+        uses: actions/cache@5a3ec84eff668545956fd18022155c47e93e2684
+        with:
+          path: "~/.pub-cache/hosted"
+          key: "os:ubuntu-latest;pub-cache-hosted;sdk:dev;packages:build_runner_core;commands:command_2"
+          restore-keys: |
+            os:ubuntu-latest;pub-cache-hosted;sdk:dev;packages:build_runner_core
+            os:ubuntu-latest;pub-cache-hosted;sdk:dev
+            os:ubuntu-latest;pub-cache-hosted
+            os:ubuntu-latest
+      - name: Setup Dart SDK
+        uses: dart-lang/setup-dart@f0ead981b4d9a35b37f30d36160575d60931ec30
+        with:
+          sdk: dev
+      - id: checkout
+        name: Checkout repository
+        uses: actions/checkout@93ea575cb5d8a053eaa0ac8fa3b40d7e05a33cc8
+      - id: build_runner_core_pub_upgrade
+        name: build_runner_core; dart pub upgrade
+        run: dart pub upgrade
+        if: "always() && steps.checkout.conclusion == 'success'"
+        working-directory: build_runner_core
+      - name: build_runner_core; ../tool/leak_check.sh
+        run: ../tool/leak_check.sh
+        if: "always() && steps.build_runner_core_pub_upgrade.conclusion == 'success'"
+        working-directory: build_runner_core
+    needs:
+      - job_001
+      - job_002
+      - job_003
+      - job_004
+      - job_005
+      - job_006
+      - job_007
+      - job_008
+      - job_009
+      - job_010
+      - job_011
+      - job_012
+      - job_013
+      - job_014
+      - job_015
+      - job_016
+      - job_017
+      - job_018
+      - job_019
+      - job_020
+      - job_021
+      - job_022
+      - job_023
+      - job_024
+      - job_025
+      - job_026
+      - job_027
+      - job_028
+      - job_029
+      - job_030
+      - job_031
+      - job_032
+      - job_033
+      - job_034
+      - job_035
+      - job_036
+      - job_037
+      - job_038
+      - job_039
+      - job_040
+      - job_041
+      - job_042
+      - job_043
+      - job_044
+  job_046:
     name: "e2e_test; linux; Dart dev; PKG: build_runner; `dart test -t integration --total-shards 5 --shard-index 0 --test-randomize-ordering-seed=random --no-chain-stack-traces -j 1`"
     runs-on: ubuntu-latest
     steps:
@@ -1754,7 +1829,8 @@ jobs:
       - job_042
       - job_043
       - job_044
-  job_046:
+      - job_045
+  job_047:
     name: "e2e_test; linux; Dart dev; PKG: build_runner; `dart test -t integration --total-shards 5 --shard-index 1 --test-randomize-ordering-seed=random --no-chain-stack-traces -j 1`"
     runs-on: ubuntu-latest
     steps:
@@ -1829,7 +1905,8 @@ jobs:
       - job_042
       - job_043
       - job_044
-  job_047:
+      - job_045
+  job_048:
     name: "e2e_test; linux; Dart dev; PKG: build_runner; `dart test -t integration --total-shards 5 --shard-index 2 --test-randomize-ordering-seed=random --no-chain-stack-traces -j 1`"
     runs-on: ubuntu-latest
     steps:
@@ -1904,7 +1981,8 @@ jobs:
       - job_042
       - job_043
       - job_044
-  job_048:
+      - job_045
+  job_049:
     name: "e2e_test; linux; Dart dev; PKG: build_runner; `dart test -t integration --total-shards 5 --shard-index 3 --test-randomize-ordering-seed=random --no-chain-stack-traces -j 1`"
     runs-on: ubuntu-latest
     steps:
@@ -1979,7 +2057,8 @@ jobs:
       - job_042
       - job_043
       - job_044
-  job_049:
+      - job_045
+  job_050:
     name: "e2e_test; linux; Dart dev; PKG: build_runner; `dart test -t integration --total-shards 5 --shard-index 4 --test-randomize-ordering-seed=random --no-chain-stack-traces -j 1`"
     runs-on: ubuntu-latest
     steps:
@@ -2054,7 +2133,8 @@ jobs:
       - job_042
       - job_043
       - job_044
-  job_050:
+      - job_045
+  job_051:
     name: "e2e_test; linux; Dart main; PKG: _test; `dart test --total-shards 3 --shard-index 0 --test-randomize-ordering-seed=random`"
     runs-on: ubuntu-latest
     steps:
@@ -2129,7 +2209,8 @@ jobs:
       - job_042
       - job_043
       - job_044
-  job_051:
+      - job_045
+  job_052:
     name: "e2e_test; linux; Dart main; PKG: _test; `dart test --total-shards 3 --shard-index 1 --test-randomize-ordering-seed=random`"
     runs-on: ubuntu-latest
     steps:
@@ -2204,7 +2285,8 @@ jobs:
       - job_042
       - job_043
       - job_044
-  job_052:
+      - job_045
+  job_053:
     name: "e2e_test; linux; Dart main; PKG: _test; `dart test --total-shards 3 --shard-index 2 --test-randomize-ordering-seed=random`"
     runs-on: ubuntu-latest
     steps:
@@ -2279,7 +2361,8 @@ jobs:
       - job_042
       - job_043
       - job_044
-  job_053:
+      - job_045
+  job_054:
     name: "e2e_test; linux; Dart main; PKG: build_runner; `dart test -t integration --total-shards 5 --shard-index 0 --test-randomize-ordering-seed=random --no-chain-stack-traces -j 1`"
     runs-on: ubuntu-latest
     steps:
@@ -2354,7 +2437,8 @@ jobs:
       - job_042
       - job_043
       - job_044
-  job_054:
+      - job_045
+  job_055:
     name: "e2e_test; linux; Dart main; PKG: build_runner; `dart test -t integration --total-shards 5 --shard-index 1 --test-randomize-ordering-seed=random --no-chain-stack-traces -j 1`"
     runs-on: ubuntu-latest
     steps:
@@ -2429,7 +2513,8 @@ jobs:
       - job_042
       - job_043
       - job_044
-  job_055:
+      - job_045
+  job_056:
     name: "e2e_test; linux; Dart main; PKG: build_runner; `dart test -t integration --total-shards 5 --shard-index 2 --test-randomize-ordering-seed=random --no-chain-stack-traces -j 1`"
     runs-on: ubuntu-latest
     steps:
@@ -2504,7 +2589,8 @@ jobs:
       - job_042
       - job_043
       - job_044
-  job_056:
+      - job_045
+  job_057:
     name: "e2e_test; linux; Dart main; PKG: build_runner; `dart test -t integration --total-shards 5 --shard-index 3 --test-randomize-ordering-seed=random --no-chain-stack-traces -j 1`"
     runs-on: ubuntu-latest
     steps:
@@ -2579,7 +2665,8 @@ jobs:
       - job_042
       - job_043
       - job_044
-  job_057:
+      - job_045
+  job_058:
     name: "e2e_test; linux; Dart main; PKG: build_runner; `dart test -t integration --total-shards 5 --shard-index 4 --test-randomize-ordering-seed=random --no-chain-stack-traces -j 1`"
     runs-on: ubuntu-latest
     steps:
@@ -2654,7 +2741,8 @@ jobs:
       - job_042
       - job_043
       - job_044
-  job_058:
+      - job_045
+  job_059:
     name: "e2e_test; windows; Dart main; PKG: _test; `dart test --total-shards 3 --shard-index 0 --test-randomize-ordering-seed=random`"
     runs-on: windows-latest
     steps:
@@ -2719,7 +2807,8 @@ jobs:
       - job_042
       - job_043
       - job_044
-  job_059:
+      - job_045
+  job_060:
     name: "e2e_test; windows; Dart main; PKG: _test; `dart test --total-shards 3 --shard-index 1 --test-randomize-ordering-seed=random`"
     runs-on: windows-latest
     steps:
@@ -2784,7 +2873,8 @@ jobs:
       - job_042
       - job_043
       - job_044
-  job_060:
+      - job_045
+  job_061:
     name: "e2e_test; windows; Dart main; PKG: _test; `dart test --total-shards 3 --shard-index 2 --test-randomize-ordering-seed=random`"
     runs-on: windows-latest
     steps:
@@ -2849,7 +2939,8 @@ jobs:
       - job_042
       - job_043
       - job_044
-  job_061:
+      - job_045
+  job_062:
     name: "e2e_test_cron; linux; Dart main; PKG: _test; `dart test`"
     runs-on: ubuntu-latest
     if: "github.event_name == 'schedule'"
@@ -2941,7 +3032,8 @@ jobs:
       - job_058
       - job_059
       - job_060
-  job_062:
+      - job_061
+  job_063:
     name: "e2e_test_cron; windows; Dart main; PKG: _test; `dart test`"
     runs-on: windows-latest
     if: "github.event_name == 'schedule'"
@@ -3023,7 +3115,8 @@ jobs:
       - job_058
       - job_059
       - job_060
-  job_063:
+      - job_061
+  job_064:
     name: Notify failure
     runs-on: ubuntu-latest
     if: "(github.event_name == 'push' || github.event_name == 'schedule') && failure()"
@@ -3097,3 +3190,4 @@ jobs:
       - job_060
       - job_061
       - job_062
+      - job_063
diff --git a/build_runner_core/mono_pkg.yaml b/build_runner_core/mono_pkg.yaml
index b98d8f32b1..3ec53f6ecc 100644
--- a/build_runner_core/mono_pkg.yaml
+++ b/build_runner_core/mono_pkg.yaml
@@ -13,3 +13,7 @@ stages:
     os:
     - linux
     - windows
+- leak_check:
+  - group:
+    - command: ../tool/leak_check.sh
+    sdk: dev
diff --git a/build_runner_core/test/invalidation/invalidation_leak_checker.dart b/build_runner_core/test/invalidation/invalidation_leak_checker.dart
new file mode 100644
index 0000000000..7fa5319272
--- /dev/null
+++ b/build_runner_core/test/invalidation/invalidation_leak_checker.dart
@@ -0,0 +1,39 @@
+// Copyright (c) 2025, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+import 'dart:io';
+
+import 'invalidation_tester.dart';
+
+/// Checks for memory leaks.
+///
+/// Runs many incremental builds, prints the average increase in memory usage
+/// per build.
+///
+/// Run using `tool/leak_check.sh`.
+void main(List<String> arguments) async {
+  final tester = InvalidationTester(testIsRunning: false);
+
+  tester.sources(['a.1']);
+
+  tester.builder(from: '.1', to: '.2')
+    ..reads('.1')
+    ..resolvesOther('a.1')
+    ..writes('.2');
+
+  await tester.build();
+  await tester.build(change: 'a.1');
+
+  // `.dart_tool/build_resolvers/sdk.sum` will be calculated and written if it
+  // does not yet exist, leading to very different memory usage. Users should
+  // run with the arg `setup` first to make sure this has happened.
+  if (arguments.contains('setup')) return;
+
+  final before = ProcessInfo.currentRss;
+  for (var i = 0; i != 5000; ++i) {
+    await tester.build(change: 'a.1');
+  }
+  final after = ProcessInfo.currentRss;
+  print((after - before) ~/ 5000);
+}
diff --git a/build_runner_core/test/invalidation/invalidation_tester.dart b/build_runner_core/test/invalidation/invalidation_tester.dart
index 1c673d7adf..5b2ab0e3b6 100644
--- a/build_runner_core/test/invalidation/invalidation_tester.dart
+++ b/build_runner_core/test/invalidation/invalidation_tester.dart
@@ -22,6 +22,8 @@ import 'package:test/test.dart';
 /// to the path `lib/a.dart`; all names map to the package `pkg`. "Hidden" asset
 /// IDs under `.dart_tool` are mapped back to the same namespace.
 class InvalidationTester {
+  final bool testIsRunning;
+
   /// The source assets on disk before the first build.
   final Set<AssetId> _sourceAssets = {};
 
@@ -65,6 +67,8 @@ class InvalidationTester {
   /// Output number, for writing outputs that are different.
   int _outputNumber = 0;
 
+  InvalidationTester({this.testIsRunning = true});
+
   /// Starts logging test setup.
   ///
   /// Useful if test setup is random or generated.
@@ -231,11 +235,13 @@ class InvalidationTester {
       testingBuilderConfig: false,
     );
     final logString = log.toString();
-    printOnFailure(
-      '=== build log #${++_buildNumber} ===\n\n'
-      '${_setupLog.map((l) => '  $l\n').join('')}'
-      '${logString.trimAndIndent}',
-    );
+    if (testIsRunning) {
+      printOnFailure(
+        '=== build log #${++_buildNumber} ===\n\n'
+        '${_setupLog.map((l) => '  $l\n').join('')}'
+        '${logString.trimAndIndent}',
+      );
+    }
     if (_logSetup) _setupLog.clear();
     readerWriter = testBuildResult.readerWriter;
 
diff --git a/tool/ci.sh b/tool/ci.sh
index aa5decff6e..5c9aaa637b 100755
--- a/tool/ci.sh
+++ b/tool/ci.sh
@@ -1,5 +1,5 @@
 #!/bin/bash
-# Created with package:mono_repo v6.6.2
+# Created with package:mono_repo v6.6.3
 
 # Support built in commands on windows out of the box.
 
@@ -75,6 +75,10 @@ for PKG in ${PKGS}; do
         echo 'dart run build_runner test -- -p vm test/configurable_uri_test.dart --test-randomize-ordering-seed=random'
         dart run build_runner test -- -p vm test/configurable_uri_test.dart --test-randomize-ordering-seed=random || EXIT_CODE=$?
         ;;
+      command_2)
+        echo '../tool/leak_check.sh'
+        ../tool/leak_check.sh || EXIT_CODE=$?
+        ;;
       format)
         echo 'dart format --output=none --set-exit-if-changed .'
         dart format --output=none --set-exit-if-changed . || EXIT_CODE=$?
diff --git a/tool/leak_check.sh b/tool/leak_check.sh
new file mode 100755
index 0000000000..1cbe9d7cf0
--- /dev/null
+++ b/tool/leak_check.sh
@@ -0,0 +1,33 @@
+#!/bin/bash --
+
+# Checks for memory leaks.
+#
+# Runs many incremental builds, prints the average increase in memory usage
+# per build.
+#
+# Exits with an error code if the hard-coded max leak size is exceeded.
+
+if test -d build_runner_core; then
+  cd build_runner_core
+fi
+
+dart test/invalidation/invalidation_leak_checker.dart setup
+
+leak_amount=$(dart test/invalidation/invalidation_leak_checker.dart)
+leak_limit=60000
+
+if test $((leak_amount)) -gt 60000; then
+  echo "Measured leak size $leak_amount > $leak_limit, failing!"
+  exit 1
+else
+  echo "Measured leak size $leak_amount < $leak_limit."
+  exit 0
+fi
+
+# Measurement history
+#
+# Initial check-in:
+#   52455, 52332, 52308
+#
+# Initial check-in with https://dart-review.googlesource.com/c/sdk/+/441740:
+#  21482, 11568, 13186