feat(rewarding): add DelegateDistributed batched log encoder (IIP-59 PR 4.7)

[envestcc]

Summary

Adds the encoder primitives for IIP-59 §3.2's per-delegate batched DelegateDistributed receipt log. distributeToVoters (PR 3', upcoming) will call Pack once per delegate at epoch close and wrap the returned (topics, data) into an *action.Log.

Batching keeps total epoch-last-block logs bounded by |topDelegates| + |orphanDrain| (~200) regardless of voter count, avoiding receipt-trie bloat under load (top 100 delegates × ~2k voters each).

Structural sibling of PR 4.5 (`delegateprofile`) and PR 4.6 (`autodeposit`) — same minimal-ABI package shape, same discipline about where the seam lands.

What lands

New package `action/protocol/rewarding/distributedlog`

• `Pack(EventArgs) → (action.Topics, []byte, error)` produces the exact wire layout an EVM-emitted `DelegateDistributed` event would produce, so `eth_getLogs` clients (and PR Try again #45's off-chain verifier) decode with stock `ethers.js` / `web3.py` against the same ABI.
• `EventArgs` mirrors §3.2's Solidity signature field-for-field: `Epoch(indexed)` + `Delegate(indexed)` + `RewardAddr` + `TotalCommission` + `TotalVoterPool` + `SnapshotHash` + `Voters[]` + `Amounts[]` + `Routings[]`.
• `Routings[]` reuses `autodeposit.Route` verbatim — PR 4.6's enum is the single source of truth for the credit/compound wire encoding.
• `SnapshotHash(voters, weights)` computes the `bytes32` digest of a delegate's frozen voter list, domain-separated (`iip59.delegatedistributed.snapshot.v1`) so verifiers can pin the exact bytes and it cannot collide with same-layout hashes from other contexts.

Semantics

Hard-error on caller-side wiring bugs:

Condition	Error
nil `Delegate` / `RewardAddr` / any `Voters[i]`	`ErrNilAddress`
nil `TotalCommission` / `TotalVoterPool` / any `Amounts[i]`	`ErrNilBigInt`
`len(Voters) != len(Amounts) != len(Routings)`	`ErrParallelArrayLengthMismatch`

The encoder is not a consensus path, so there is no per-item to degrade — loud failure surfaces PR 3' bugs. Empty voter list is NOT an error: a delegate with zero voters still emits a log for observability, per §3.2's "one log per delegate".

Explicit non-goals

• *No `action.Log` construction. Block context (height, action hash, protocol address) belongs to PR 3'. Mirrors PR 4.5 / 4.6 seams.
• No event dispatch / subscription. Encoder, not bus.
• No proto message. The event is ABI-encoded so decode-time behaviour is identical to a Solidity-emitted event.
• No orphan-drain log variant. §3.3's orphan drain emits the same shape; one encoder covers both call sites.
• No `foundationBonus` field. §3.5 leaves foundation bonus out of scope.

Test plan

• `go build ./...` clean
• `gofmt -l` clean on touched files
• `go vet ./action/protocol/rewarding/distributedlog/...` clean
• `go test ./action/protocol/rewarding/distributedlog/... -count=1 -v` — 15 tests, all green
• Regression `go test ./action/protocol/rewarding/... ./action/...` — 1104 tests across 31 packages, all green

Test coverage: happy path, zero voters, both parallel-length mismatch variants, nil-field variants (delegate/reward/commission/pool/per-voter address/per-voter amount), selector pin (golden 32 bytes so external verifiers can hard-code the same signature hash), full byte-level round-trip via the same ABI, and `SnapshotHash` determinism + empty-list constant + truncation semantics.

Stack

Branched on top of `iip-59/pr4.6-autodeposit-bridge` (#4922) because this PR imports `autodeposit.Route` at the Go-module level. Once PR 4.6 merges to `master`, the base of this PR can be flipped to `master` without conflict.

• Depended on by: PR 3' (rework `distributeVoterReward`), PR Try again #45 (off-chain verifier).
• Depends on: PR 4.6 (feat(rewarding): add AutoDeposit compound bridge for IIP-59 (PR 4.6) #4922).

🤖 Generated with Claude Code

[sonarqubecloud]

Quality Gate passed

Issues
1 New issue
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

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