[Bug]: DataFixerRegistry.register() is not atomic (check-then-put race)

[Splatcrafter]

AI REVIEWED

Module: spring-boot-starter
File: spring/autoconfigure/DataFixerRegistry.java (~line 154-160)
Severity: Medium

Summary

register() uses containsKey() followed by put() on a ConcurrentHashMap. Between these two calls, another thread could register the same domain.

if (this.fixers.containsKey(domain)) {
    throw new IllegalArgumentException("already registered");
}
this.fixers.put(domain, fixer); // race window

Suggested Fix

AetherDataFixer existing = this.fixers.putIfAbsent(domain, fixer);
if (existing != null) {
    throw new IllegalArgumentException("DataFixer already registered for domain: " + domain);
}