Fix TSAN data races in InspectorFlags and InspectorPackagerConnection

Summary:
Fix two ThreadSanitizer data races caught by the messenger_demo integration test under dev-tsan mode.

**InspectorFlags**: `loadFlagsAndAssertUnchanged()` reads and writes `cachedValues_` without synchronization. The main thread calls it via `getIsProfilingBuild()` while the JS thread calls it via `getNetworkInspectionEnabled()`, racing on the shared `optional<Values>`. Add a `std::mutex` to protect `cachedValues_` access. The lock is taken after computing `newValues` from feature flags, so flag reads stay outside the critical section.

**InspectorPackagerConnection**: `Impl::connect()` is called from the main thread but accesses `webSocket_` which is also read by `didFailWithError()` on the inspector thread. Dispatch the body of `connect()` to the inspector thread via `scheduleCallback()`, matching the pattern `reconnect()` already uses.

Changelog: [Internal]

Differential Revision: D101809616

Author: javache

packages/react-native/ReactCommon/jsinspector-modern/InspectorFlags.cpp

@@ -50,7 +50,9 @@ bool InspectorFlags::getPerfIssuesEnabled() const {
 }
 
 void InspectorFlags::dangerouslyResetFlags() {
-  *this = InspectorFlags{};
+  cachedValues_.reset();
+  inconsistentFlagsStateLogged_ = false;
+  fuseboxDisabledForTest_ = false;
 }
 
 void InspectorFlags::dangerouslyDisableFuseboxForTest() {
@@ -84,6 +86,8 @@ const InspectorFlags::Values& InspectorFlags::loadFlagsAndAssertUnchanged()
       .perfIssuesEnabled = ReactNativeFeatureFlags::perfIssuesEnabled(),
   };
 
+  // Protect against concurrent calls
+  std::lock_guard<std::mutex> lock(mutex_);
   if (cachedValues_.has_value() && !inconsistentFlagsStateLogged_) {
     if (cachedValues_ != newValues) {
       LOG(ERROR)
@@ -93,7 +97,6 @@ const InspectorFlags::Values& InspectorFlags::loadFlagsAndAssertUnchanged()
       inconsistentFlagsStateLogged_ = true;
     }
   }
-
   cachedValues_ = newValues;
 
   return cachedValues_.value();

packages/react-native/ReactCommon/jsinspector-modern/InspectorFlags.h

@@ -7,6 +7,7 @@
 
 #pragma once
 
+#include <mutex>
 #include <optional>
 
 namespace facebook::react::jsinspector_modern {
@@ -82,9 +83,10 @@ class InspectorFlags {
 
   InspectorFlags() = default;
   InspectorFlags(const InspectorFlags &) = delete;
-  InspectorFlags &operator=(const InspectorFlags &) = default;
+  InspectorFlags &operator=(const InspectorFlags &) = delete;
   ~InspectorFlags() = default;
 
+  mutable std::mutex mutex_;
   mutable std::optional<Values> cachedValues_;
   mutable bool inconsistentFlagsStateLogged_{false};
   bool fuseboxDisabledForTest_{false};

packages/react-native/ReactCommon/jsinspector-modern/InspectorPackagerConnection.cpp

@@ -328,12 +328,21 @@ bool InspectorPackagerConnection::Impl::isConnected() const {
 }
 
 void InspectorPackagerConnection::Impl::connect() {
-  if (closed_) {
-    LOG(ERROR)
-        << "Illegal state: Can't connect after having previously been closed.";
-    return;
-  }
-  webSocket_ = delegate_->connectWebSocket(url_, weak_from_this());
+  delegate_->scheduleCallback(
+      [weakSelf = weak_from_this()]() mutable {
+        auto strongSelf = weakSelf.lock();
+        if (!strongSelf) {
+          return;
+        }
+        if (strongSelf->closed_) {
+          LOG(ERROR)
+              << "Illegal state: Can't connect after having previously been closed.";
+          return;
+        }
+        strongSelf->webSocket_ = strongSelf->delegate_->connectWebSocket(
+            strongSelf->url_, std::move(weakSelf));
+      },
+      0ms);
 }
 
 void InspectorPackagerConnection::Impl::reconnect() {