Important caveats where non-mining nodes still matter: - Pr…

Important caveats where non-mining nodes still matter:
- Propagation: Non-mining full nodes won’t relay invalid blocks, so dissemination is limited even before miners see them.
- Miner mistakes (SPV/headers-first): If a miner mines on a header before full validation (it has happened, e.g., around BIP66 in 2015), they can accidentally extend an invalid block. Robust non-mining validation/relay helps surface and isolate those errors.
- Policy/incentives in contentious changes: If miners coordinate to follow rules that non-mining economic nodes reject, the latter won’t accept those blocks for deposits/payments. Miners then have strong incentives to switch back. Non-mining nodes don’t vote block-by-block, but they define what the market treats as valid.