Fix: Prevent uncatchable capability error from DefineFastFlag in client scripts

[4bdullah0]

## The Problem

When I tried using React-Roblox in a LocalScript, my app immediately crashed with this error:

The current thread cannot call 'DefineFastFlag' (lacking capability RobloxScript)
Error occurred, no output from Luau.

The crash happens in RobloxComponentProps.lua when it tries to set up FFlagReactFixBindingMemoryLeak.

How I Found the Issue

At first, I thought it was my code. I tried:

1. Switching from a Folder to a ScreenGui for the root container
2. Moving around the StrictMode wrapper

Nothing worked. The app kept crashing before anything would render, so I dug into the library source.

What's Actually Wrong

Turns out game:DefineFastFlag() needs a special permission called RobloxScript capability. Only Roblox's internal server scripts have this - regular LocalScripts don't.

The library tries to handle errors with xpcall:

local _, FFlagReactFixBindingMemoryLeak = xpcall(function()
	return game:DefineFastFlag("ReactFixBindingMemoryLeak", false)
end, function()
	return true
end)

But here's the catch: capability errors in Roblox can't be caught. Not by pcall, not by xpcall. They just blow right past error handlers and kill your script.

The Fix

Instead of trying to catch an uncatchable error, just check if we're in the right context first:

local FFlagReactFixBindingMemoryLeak = true -- Safe default

local RunService = game:GetService("RunService")
local isServerContext = RunService:IsServer() and not RunService:IsClient()

if isServerContext then
	local success, result = pcall(function()
		return game:DefineFastFlag("ReactFixBindingMemoryLeak", false)
	end)
	
	if success and typeof(result) == "boolean" then
		FFlagReactFixBindingMemoryLeak = result
	end
end

Why This Works Better

• No more crashes in client scripts
• Server scripts can still use the FastFlag if needed
• Everyone gets the memory leak fix (which is the whole point)
• The code makes it obvious what's happening and why

What I Tested

I verified this works with:

• My roblox-ts project running in ReplicatedStorage
• Basic React rendering using createRoot and a ScreenGui
• Both client and server contexts

No errors, everything renders properly now.

Who This Affects

Anyone using React-Roblox in a client context - whether you're using roblox-ts or writing Luau directly.

---

What Changed:

• modules/react-roblox/src/client/RobloxComponentProps.lua

Change Type:

• Bug fix (doesn't break anything existing)