Updates React Native Windows to nightly 0.85.0-nightly-20260303-c26dbe286 (Mar 3, 2026) (#16300)

* Integrate RN 0.85.0-nightly-20260303-c26dbe286 (with conflicts)

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

* Resolve conflicts for RN 0.85.0-nightly-20260303-c26dbe286 integration

Resolved 4 override conflicts (AccessibilityPrimitives.h, WindowsTextInputNativeComponent.js, BaseViewConfig.win32.js, BaseViewConfig.windows.js) and removed two orphaned ReactNativeViewAttributes overrides whose upstream base file was deleted.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

* Bump flow-bin to 0.303.0 to match upstream flowconfig

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

* Change files

* Fix native build for RN 0.85.0-nightly-20260303 upstream API changes

Adapt RNW native code to upstream changes surfaced by the playground-composition build:
- EventEmitter const removal: SharedEventEmitter is now shared_ptr<EventEmitter> (non-const). Drop const from emitter creation in AbiComponentDescriptor/AbiViewComponentDescriptor createFamily (mirrors upstream ConcreteComponentDescriptor) and const_pointer_cast at the EventEmitterForComponent boundary.
- ShadowNode::Unshared alias removed upstream: use std::shared_ptr<ShadowNode> directly in AbiPortalShadowNode::layout.
- ParagraphComponentDescriptor.cpp deleted upstream (now header-only): remove stale ClCompile entry from Shared.vcxitems.

Validated: playground-composition builds, deploys, launches, and loads the RNTester JS bundle.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

* Enable core.longpaths in override scratch repo to fix validate-overrides on Windows

Newer RN nightlies include deeply-nested upstream paths that exceed the
260-char MAX_PATH limit, causing 'git checkout' to fail with 'Filename too
long' during validate-overrides on Windows CI agents.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

* Change files

---------

Co-authored-by: Anukrati Agrawal <anuagra@microsoft.com>
Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Author: 3 people

change/@office-iss-react-native-win32-ac9d508c-d6cc-4231-8206-b71ec3148ec0.json

@@ -0,0 +1,7 @@
+{
+  "type": "prerelease",
+  "comment": "Integrate RN 0.85.0-nightly-20260303-c26dbe286",
+  "packageName": "@office-iss/react-native-win32",
+  "email": "email not defined",
+  "dependentChangeType": "patch"
+}

change/@react-native-windows-automation-channel-d46f5a17-4214-4ec0-a7e0-6cfa159173ae.json

@@ -0,0 +1,7 @@
+{
+  "type": "prerelease",
+  "comment": "Integrate RN 0.85.0-nightly-20260303-c26dbe286",
+  "packageName": "@react-native-windows/automation-channel",
+  "email": "email not defined",
+  "dependentChangeType": "patch"
+}

change/@react-native-windows-cli-7bdc1771-a53b-49c7-a7ef-dc6eae80624b.json

@@ -0,0 +1,7 @@
+{
+  "type": "prerelease",
+  "comment": "Integrate RN 0.85.0-nightly-20260303-c26dbe286",
+  "packageName": "@react-native-windows/cli",
+  "email": "email not defined",
+  "dependentChangeType": "patch"
+}

change/@react-native-windows-perf-testing-bb5ecb0d-6534-4b7a-9b84-1543bcd38f8c.json

@@ -0,0 +1,7 @@
+{
+  "type": "prerelease",
+  "comment": "Integrate RN 0.85.0-nightly-20260303-c26dbe286",
+  "packageName": "@react-native-windows/perf-testing",
+  "email": "email not defined",
+  "dependentChangeType": "patch"
+}

change/react-native-platform-override-f010562c-1000-44c0-bd17-1fff61d586b6.json

@@ -0,0 +1,7 @@
+{
+  "type": "prerelease",
+  "comment": "Enable core.longpaths in override scratch repo to fix validate-overrides on Windows for deeply-nested upstream paths",
+  "packageName": "react-native-platform-override",
+  "email": "email not defined",
+  "dependentChangeType": "patch"
+}

change/react-native-windows-1dffc52b-2141-47e7-94cd-012e1d39b247.json

@@ -0,0 +1,7 @@
+{
+  "type": "prerelease",
+  "comment": "Integrate RN 0.85.0-nightly-20260303-c26dbe286",
+  "packageName": "react-native-windows",
+  "email": "email not defined",
+  "dependentChangeType": "patch"
+}

change/react-native-windows-init-4869dba6-2341-4fc1-bdb3-8a6234092e9e.json

@@ -0,0 +1,7 @@
+{
+  "type": "prerelease",
+  "comment": "Integrate RN 0.85.0-nightly-20260303-c26dbe286",
+  "packageName": "react-native-windows-init",
+  "email": "email not defined",
+  "dependentChangeType": "patch"
+}

package.json

@@ -53,7 +53,7 @@
     "prettier": "^3.6.2",
     "prettier-plugin-hermes-parser": "0.21.1",
     "react": "19.2.3",
-    "react-native": "0.85.0-nightly-20260224-42cd0f041",
+    "react-native": "0.85.0-nightly-20260303-c26dbe286",
     "react-native-platform-override": "workspace:*",
     "typescript": "5.0.4"
   },

packages/@office-iss/react-native-win32-tester/overrides.json

@@ -5,7 +5,7 @@
   "excludePatterns": [
     "src/js/examples-win32/**"
   ],
-  "baseVersion": "0.85.0-nightly-20260224-42cd0f041",
+  "baseVersion": "0.85.0-nightly-20260303-c26dbe286",
   "overrides": [
     {
       "type": "patch",

packages/@office-iss/react-native-win32-tester/package.json

@@ -11,15 +11,15 @@
     "validate-overrides": "react-native-platform-override validate"
   },
   "dependencies": {
-    "@react-native/tester": "0.85.0-nightly-20260224-42cd0f041",
+    "@react-native/tester": "0.85.0-nightly-20260303-c26dbe286",
     "@typescript-eslint/eslint-plugin": "^8.36.0",
     "@typescript-eslint/parser": "^8.36.0",
     "flow-enums-runtime": "^0.0.6"
   },
   "peerDependencies": {
     "@office-iss/react-native-win32": "^0.0.0-canary.311",
     "react": "19.2.3",
-    "react-native": "0.85.0-nightly-20260224-42cd0f041"
+    "react-native": "0.85.0-nightly-20260303-c26dbe286"
   },
   "devDependencies": {
     "@office-iss/react-native-win32": "^0.0.0-canary.311",
@@ -32,7 +32,7 @@
     "just-scripts": "^1.3.3",
     "prettier": "^3.6.2",
     "react": "19.2.3",
-    "react-native": "0.85.0-nightly-20260224-42cd0f041",
+    "react-native": "0.85.0-nightly-20260303-c26dbe286",
     "react-native-platform-override": "0.0.0-canary.1022",
     "typescript": "5.0.4"
   },