ops: pre-fork baseline and check for the Zero8 (v0.8.0) upgrade

[gnanam1990]

Arc testnet forks to arc-node v0.8.0 today at 15:00 UTC. This lands the pre-fork baseline, a read-only check to diff against afterwards, and the analysis of what the upgrade can actually reach.

What to run after the fork

./scripts/hardfork-check > docs/hardfork/zero8-post.txt
diff docs/hardfork/zero8-pre.txt docs/hardfork/zero8-post.txt

gasPrice and the timestamp move. Everything else moving is a finding — no Snapfall transaction is submitted in between. The script submits nothing and needs no key.

v0.8.0 impact: near zero

Five of six breaking changes are node-operator only (--rpc.admin, mandatory denylist, stricter ARC_* validation, snapshot --chain, pruning interval). We run no node.

The sixth changes JSON-RPC error text on insufficient balance and asks clients to update their error parsers. We have none — the only strings.Contains against an error in the daemon is a SQLite UNIQUE constraint match in approval/lifecycle.go, and no RPC error text drives control flow. v0.7.2's EIP-155 requirement and 30M gas cap were re-checked; both hold.

The exposure worth watching isn't on that list: Zero8 changes gas accounting and state-clearing semantics, and settlement clears storage when an advance closes. Estimation plus 20% headroom should absorb it, and no gas limit is hardcoded — but if anything fails after the fork, compare gasUsed first.

Separate finding, predating the fork

The public RPC no longer serves transactions or receipts by hash. Every hash in docs/addresses.md returns null; blocks and logs are still served, so the tx-hash index is pruned and the chain is intact.

That page names the RPC as "the primary verification path" precisely because ArcScan's hash lookups are broken — so both of a reader's routes are currently dead, and the settlement proof can't be checked as written.

The evidence survives. eth_getLogs over the settlement block still shows the pool repaid at logIndex 12 (561000) and the operator paid at 15 (439000) — pool first, exactly as §4 claims. The check now asserts that ordering and those amounts every run instead of counting logs. An archive endpoint (ARC_ARCHIVE_RPC) still resolves the hash directly.

docs/addresses.md still needs its verification commands reworked before submission. The numbers are right; the way it tells a reader to check them is not. Not done in this PR.

Chain state has moved past the docs

An 0.60 advance is open across the upgrade. Rate is 7000 (docs say 6500), four accepted jobs (docs say three), reserve 8240 (docs say 5640) — a fourth job settled after 8 Aug.

Verified before committing, at 103f0be

forge build	clean
forge test	119 passed, 0 failed
go build ./...	clean
go test ./...	exit 0, 33 packages ok

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Summary by cubic

Lands the pre-fork baseline and a read-only fingerprint script for the Zero8 (v0.8.0) hardfork on Arc testnet, along with an analysis of what the upgrade can and cannot affect. All three layers (contracts, daemon, sidecar) are green pre-fork; scripts/hardfork-check submits nothing, needs no key, and is diffed before and after — gasPrice and the timestamp are expected to differ, anything else moving is a finding.

• The script records the repo commit it ran at; SNAPFALL_REPO overrides the location when it's run from a copy outside the checkout, so the post-fork run doesn't depend on which branch is checked out.

v0.8.0 impact

• Five of six breaking changes are node-operator only; Snapfall runs no node.
• The sixth changes JSON-RPC error text on insufficient balance; no code matches on RPC error text, so it's cosmetic.
• Gas accounting and state-clearing changes are the real exposure; estimation plus 20% headroom should absorb them.

Pre-existing RPC finding

• The public RPC pruned its tx-hash index; transactions and receipts return null by hash, but blocks and logs still work.
• The settlement proof still verifies via eth_getLogs; the script asserts the waterfall's ordering and amounts on every run.
• Chain state is ahead of docs/addresses.md (rate 7000 vs 6500, four accepted jobs vs three); that doc's verification commands still need reworking.

^{Written for commit 2282a97. Summary will update on new commits.}

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