[tooling] PublicNode BSC fallback is pruned — archive eth_call returns 'missing trie node'

[obchain]

Refs #52

File: scripts/anvil_fork.sh

Problem

BSC-PublicNode (bsc-rpc.publicnode.com) retains only ~128 recent blocks of state. Any anvil fork that performs eth_call against a block older than that returns 'missing trie node'. dRPC primary is genuine archive; PublicNode fallback is not. A fallback that silently delivers broken behavior is worse than hard-fail.

Fix

Replace PublicNode with an actual archive endpoint. Options:

• BNB Chain official archive endpoints (limited, rate-limited but archive)
• Chainstack archive (free tier with email signup)
• ankr.com/rpc/ (paid, but single-transaction archive reads sometimes free)
• Fork probe: test state at block-1000 before accepting the upstream. Fail fast if state missing.

Document endpoint requirements in README: 'requires BSC archive RPC; PublicNode is NOT archive'.

[obchain]

Fixed on feat/24-anvil-fork (ffae806): pruned PublicNode fallback removed; script hard-errors with override guidance.