Bug: Turkish Locale - Potential Header/Key resolution failure due to case-insensitive TreeMap serialization

[yalcinmuhammed]

Bug Description

Applications utilizing this SDK on a Turkish OS locale face unexpected anomalies or token crashes during HTTP header parsing.

Root Cause

In openai-java-core/src/main/kotlin/com/openai/core/http/Headers.kt (Line 38), the headers map is initialized using a locale-dependent comparison mechanism:

private val map: MutableMap<String, MutableList<String>> =
    TreeMap(String.CASE_INSENSITIVE_ORDER)

Java's native String.CASE_INSENSITIVE_ORDER internally triggers Character.toLowerCase(). On a Turkish host machine, this converts the capital letter I in "OpenAI-Organization" into a dotless ı, turning it into "openaı-organization".
This causes key lookup failures or broken token states when downstream interceptors (like OkHttp) process standard ASCII headers.

Related Upstream Issue

This is the Java/Kotlin ecosystem equivalent of the localization bug found in the Node SDK.

• Linked Node Issue: Bug: TypeError: Header name must be a valid HTTP token ["openaı-organization"] on Turkish Windows/Locale openai-node#1928

Suggested Official Fix

The TreeMap should enforce a locale-invariant comparator (such as Locale.ROOT) to guarantee strict ASCII/English-based casing rules across all operating systems:

TreeMap { s1, s2 -> s1.lowercase(java.util.Locale.ROOT).compareTo(s2.lowercase(java.util.Locale.ROOT)) }

[arimu1]

I opened and then closed #817 after verifying the premise.

TreeMap(String.CASE_INSENSITIVE_ORDER) is not affected by Turkish locale: the comparator uses Unicode case mapping (Character.toUpperCase/toLowerCase), not String.toLowerCase(). Under Locale("tr","TR"), header keys still match across case.

Turkish dotted/dotless I only bites locale-sensitive String case folding. Happy to help if there is a different repro (e.g. a code path that lowercases header names with the default locale).