`main` branch of celestia-node should target compatibility with celestia-app v9

[rootulp]

Context

celestia-node/go.mod

Line 13 in bd4fd29

github.com/celestiaorg/celestia-app/v8 v8.0.0-20260319203113-2ec59a0a61e4

Problem

The main branch of celestia-node isn't compatible with the main branch of celestia-app. IMO the main branch in celestia-node should use the latest official release of celestia-app, likely v8.0.1-mocha for now or v8.0.1 when that is released.

We don't need Fibre support in celestia-node until v10 so we also don't need go-square v4 on celestia-node main for a while.

Tangent: This is why Rachid is unlinking Fibre from celestia-app because we plan on creating a celestia-app v9 release which doesn't use Fibre. celestia-node main should likely target compatibility with celestia-app v9.

Proposal

• Update the go.mod on main to use v8.0.1-mocha. This may involve removing Fibre features from celestia-node or placing them behind a build flag like feat!: unlink the fibre module by default and allow adding it using a build tag celestia-app#6957

[vgonkivs]

This version were needed for the fibre work. It was updated along with the go-squarev4

[rootulp]

Yes but Fibre won't be released until celestia-app v10. We'll need a compatible celestia-node release for celestia-app v9 which I think should be released from celestia-node main