chore(fast-inbox): delete legacy node message paths (A-1388)

[spalladino]

Node cleanup for the Fast Inbox (AZIP-22) project — removes the legacy L1-to-L2 message paths the flip (#24789) left dead. Sits on the Fast Inbox stack (#24784..#24792); base is spl/a-1387-circuits-cleanup.

What's removed

• stdlib / p2p: computeInHashFromL1ToL2Messages and the whole in_hash.ts; the inHash field on BlockProposal (constructor, signed payload, wire, and the createBlockProposal validator-interface argument); the CheckpointProposal.getBlockProposal inHash pass-through; the padded per-checkpoint InboxLeaf helpers (smallestIndexForCheckpoint / indexRangeForCheckpoint / checkpointNumberFromIndex); the legacy getL1ToL2Messages(checkpointNumber) member from the L1ToL2MessageSource and archiver RPC interfaces.
• archiver: the legacy per-checkpoint getL1ToL2Messages flow, the padded per-checkpoint index invariants, the inboxTreeInProgress readiness gate + L1ToL2MessagesNotReadyError, and the 128-bit keccak rolling hash. InboxMessage now carries only the compact global index and the full-width consensus rolling hash (the vacuous derived checkpointNumber and the 128-bit rollingHash are gone). Reorg detection compares the local consensus rolling hash and total against the Inbox's current rolling-hash bucket (new getBucket / getCurrentBucketSeq / getCurrentBucket wrappers) instead of the 128-bit getState.
• sequencer / validator: the dead inHash = Fr.ZERO threading through the checkpoint proposal job and the validator/validation-service create-proposal path, plus the dead in_hash_mismatch validation-failure reason.
• world-state: the no-op first-in-checkpoint padding alias and the obsolete non-first-block-empty-bundle transitional test (the production assertion was already removed at the flip).
• node: the public-calls simulator's dead next-checkpoint message fetch and its now-unused l1ToL2MessageSource dependency.
• config / env: AZTEC_INBOX_LAG / inboxLag from ethereum config, foundation env vars, the network-consensus-config list, the l1-contracts + spartan network defaults, and the e2e option plumbing.
• docs: THREAT_MODEL.md and the archiver README rewritten from the inHash == inbox.consume(...) model to the consensus rolling-hash / bucket model.

Format / store / wire notes

• Store version bump: ARCHIVER_DB_VERSION 8 → 9 because InboxMessage serialization dropped rollingHash + checkpointNumber and the inboxTreeInProgress singleton is gone. No migration — nodes resync (fresh rollup instance per release line, same no-migration policy as the rest of the stack).
• p2p wire format: dropping the (zeroed-since-flip) inHash shrinks the block-proposal bytes. Done as a plain removal at a release boundary (fresh networks), matching the A-1381 optional-tail precedent; the golden wire_compat_fixtures.ts buffers were regenerated. The checkpoint-proposal fixture is unaffected (it never carried inHash).
• L1 follow-through: deferred. The on-chain Inbox 128-bit messagesRollingHash accumulation + getState() / getTotalMessagesInserted() + MessageSent.rollingHash still have readers (the l1-contracts test suite and the chain_monitor TS test util), so per the plan's conditional they are left in place; deleting them is a separate L1 change.

Testing

Locally green (unit suites that run without @aztec/bb-avm-sim): archiver (561), stdlib p2p + interfaces (76), world-state synchronizer + native (74), validator-client unit (38), ethereum config (6). Suites that import @aztec/bb-avm-sim (p2p libp2p, sequencer-client, node simulator, validator integration) and full typecheck of the packages downstream of the pinned-VK blocker are CI-validated. No e2e / VK regen locally.

Review follow-up (phase-2 final review)

Four commits were appended by the final review pass:

• The env sweep removed AZTEC_INBOX_LAG from scripts/network-defaults.json while both L1 deploy-script test setUps still readUint the key, reverting before any test ran; the reads are gone.
• The p2p attestation store version is bumped 2 -> 3: it persists proposal/attestation buffers whose formats changed in this stack (checkpoint header lost inHash; block-proposal wire dropped it), and stored checkpoint attestations decode without a tolerant fallback.
• l1_publisher.integration.test.ts is reworked for streaming consumption: each checkpoint consumes every message sent while it was built, threading the previous checkpoint's rolling hash and reading the propose bucketHint from the Inbox's current bucket (the legacy inboxLag shift register is gone).
• Remaining inboxLag/inHash references are swept from the spartan environment profiles, the governance-upgrade tutorial, the validator/sequencer READMEs, and stale e2e comments.