What does "post-quantum" actually mean for a Bitcoin L2 when settlement still happens on a non-PQ L1?

The primary concern raised revolves around the security challenges at the boundaries between Layer 2 (L2) and Layer 1 (L1) networks, particularly in scenarios involving Bitcoin which is not yet post-quantum (PQ) resistant. While L2 solutions can be engineered to be PQ resistant, ensuring the security of funds during transitions or interactions between these layers remains a significant issue. This highlights an area of vulnerability that could potentially jeopardize fund safety if not adequately addressed.

The discussion also touches upon the complexity of finding definitive answers to technical questions within blockchain technology, especially those related to upgrades or integrations like making Bitcoin PQ resistant. The query suggests that solutions might vary depending on the developmental phase of the underlying technologies, such as L1 networks. It underscores a broader perspective that while developing PQ-resistant L2 solutions is beneficial, it does not completely solve security concerns if the foundational L1 network, like Bitcoin, remains vulnerable to quantum attacks. Thus, the dialogue emphasizes the need for a phased and comprehensive approach to enhancing blockchain security across different layers.