Extract _walk_replay_events for shared crown derivation

[LandynDev]

Problem → Solution

Problem — dashboard sync needs per-block crown derivation, but the logic lives inside an aggregation loop

• replay_crown_time_window returns {hotkey: blocks} totals. The dashboard's per-block grid needs (block, holders, rate) per block, and re-implementing the qualification rule in two places guarantees drift.
• → Extract _walk_replay_events — a generator yielding one record per uniform-state interval (start, end, holders, best_rate). Both the validator aggregate (replay_crown_time_window) and the new display path (replay_crown_time_window_iter) are thin wrappers around it. Single source of truth for the qualification rule (active, not busy, has rate > 0, lower-rate-wins-when-reversed).

Problem — external readers can't open the validator's SQLite without risking a write

• The alw-utils sync utility needs to tail state.db from another process.
• → ValidatorStateStore(readonly=True) opens via SQLite URI mode (file:...?mode=ro), skips DDL + journal_mode=WAL, surfaces writes as OperationalError. Plus get_rate_events_since_id(cursor) so readers can tail the autoincrement log.

Validator behaviour unchanged

The refactor is a pure rearrangement: existing replay_crown_time_window callsites in score_and_reward_miners keep producing identical numbers. Aggregating the iter wrapper's records also reproduces the totals — covered by tests/validator/test_scoring_iter.py::TestIterAggregateParity.

Test plan

• pytest tests/test_scoring_v1.py tests/validator/test_scoring_iter.py — 58/58 passing locally (47 existing + 11 new)
• ruff check allways/validator/scoring.py allways/validator/state_store.py tests/validator/ — clean
• Iter/aggregate parity test asserts SUM(credit) over the iter path equals replay_crown_time_window totals
• After merge: validator forward step latency unchanged in staging

Related PRs

Part of the miner-dashboard rollout — merge in dependency order:

1. allways-db#15 — schema
2. allways (this PR) — scoring refactor
3. alw-utils#56 — sync utility
4. das-allways#17 — API
5. allways-ui#90 — page + components

[LandynDev]

Closing — going with Option A: porting the crown-derivation logic into the alw-utils sync utility instead, so the validator's consensus code stays untouched. The dashboard accepts the drift cost (display-only, not consensus-critical). Tracking in alw-utils#56.