Would a single-player third-person shooter with this core mechanic be considered a survival horror game, or just another hardcore action horror game?
The core mechanic is a backpack-and-quick-access inventory system. The player has a backpack with virtually unlimited capacity and can store all kinds of items inside it.
However, the quick-access inventory has limited capacity, and the player can only carry a few types of items there, usually including ammo, medical supplies, explosives, and similar resources. When enemies do not detect the player, or when the player is not in combat, the player can use items from both the backpack and the quick-access inventory. Otherwise, the player can only use items from the quick-access inventory. Opening the backpack HUD does not pause the game. The backpack HUD will close automatically when enemies detect the player.
Weapons must be equipped before use, and the player can only equip two weapons at a time. Weapons consume ammo stored in the quick-access inventory.