Problem

The per-library function dict (libraryFunctionDictType) compares function names case-sensitively, while the global function dict (functionDictType) compares them case-insensitively (dictCStrCaseHash + dictSdsKeyCaseCompare). This asymmetry lets a single library register two functions whose names differ only in case, leaving the two dicts inconsistent and crashing the server on the next unlink.

Reproducer (any client with the default SCRIPTING ACL category)

FUNCTION LOAD "#!lua name=poc
redis.register_function('aaa', function() return 1 end)
redis.register_function('AAA', function() return 2 end)"
FUNCTION DELETE poc

The server aborts with:

=== ASSERTION FAILED ===
==> functions.c:332 'ret == DICT_OK' is not true
0   valkey-server   ... libraryUnlink + ...

Mechanism

1. FUNCTION LOAD — functionLibCreateFunction checks for duplicates in the per-library dict case-sensitively, so aaa and AAA are both stored there. libraryLink then inserts both into the global dict, but the second dictAdd silently returns DICT_ERR (return value ignored) because the global dict is case-insensitive. The load-path global-collision check iterates the per-library functions and looks each up in the global dict, but since AAA was never inserted there it finds no conflict and the load succeeds.
2. FUNCTION DELETE — libraryUnlink iterates the per-library dict (2 entries) and deletes each from the global dict. The first delete (aaa) succeeds; the second (AAA) resolves to the same case-insensitive slot, already removed, so dictDelete returns DICT_ERR and serverAssert(ret == DICT_OK) at functions.c:332 aborts the server.

FUNCTION LOAD REPLACE of an affected library hits the same path, since it calls libraryUnlink on the old library internally.

Requires only the SCRIPTING ACL category, granted to users by default. No admin, cluster, or special config needed.

Fix

Make libraryFunctionDictType case-insensitive (dictCStrCaseHash + dictSdsKeyCaseCompare) to match the global dict. Names differing only in case now collide at registration, and FUNCTION LOAD is rejected cleanly with Function already exists in the library. This is consistent with the long-standing case-insensitive FCALL contract (see the existing FUNCTION - test function case insensitive test).

Testing

• Reproduced the crash on unstable before the fix; confirmed the server stays up and FUNCTION LOAD is rejected after.
• Added two regression tests in tests/unit/functions.tcl. Verified they fail on pre-fix code (load wrongly succeeds, delete crashes the server) and pass after the fix.
• unit/functions: 122 passed, 0 failed. unit/scripting: 683 passed, 0 failed.