# Tasks: Re-materialization after Purge

## T1: PurgeJob and PurgeJobQueue
**File**: `tidal/src/cohort/rematerialization/job.rs`
- `JobId = [u8; 16]`, `new_job_id()` (timestamp+counter), `job_id_to_string()`
- `PurgeJobStatus` enum: Pending, Running, Succeeded, Failed, PermanentlyFailed
- `PurgeJob` struct with all lifecycle fields
- `PurgeJobQueue`: DashMap + FIFO order Vec; `submit`, `claim_pending`, `update_status`, `requeue_interrupted`, `requeue_failed`, `list_jobs`, `job_status`, `pending_count`
- Status: COMPLETE

## T2: RematerializationMetrics
**File**: `tidal/src/cohort/rematerialization/metrics.rs`
- `RematerializationMetrics` (AtomicU64 fields): `jobs_pending`, `jobs_succeeded`, `jobs_failed`, `last_job_duration_ms`, `last_job_entries_updated`
- `RematerializationMetricsSnapshot` (plain u64/usize)
- `RematerializationMetrics::new() -> Arc<Self>`, `snapshot()`
- Status: COMPLETE

## T3: Filtered WAL Replay
**File**: `tidal/src/cohort/rematerialization/replay.rs`
- `ExclusionKey { entity_id, signal_type_id, weight_bits, timestamp_nanos }` 4-tuple
- `filtered_replay(wal_dir, schema, community_id, contributions, signal_type_filter) -> Result<ReplayResult>`
- Scans WAL segments; builds scratch `CohortSignalLedger`; excludes matched events
- `ReplayStats { events_replayed, events_excluded }`
- Status: COMPLETE

## T4: Atomic Ledger Swap
**File**: `tidal/src/cohort/rematerialization/swap.rs`
- `atomic_swap(live, scratch, community_id) -> u64`
- Uses `drain_community_into` (no Clone needed); removes zero-event entries from live
- Status: COMPLETE

## T5: Audit Log
**File**: `tidal/src/cohort/rematerialization/audit.rs`
- `AuditLogWriter::open(path)`, `append(&entry) -> Result<()>`
- BLAKE3-framed binary: `[magic:4][body_len:4 LE][body:JSON][checksum:4]`
- `PurgeAuditEntry`, `make_success_entry`, `make_failure_entry`, `read_audit_log`
- `compute_verification_checksum_direct` — BLAKE3 over sorted live ledger entries
- Status: COMPLETE

## T6: CohortSignalLedger Extensions
**File**: `tidal/src/cohort/ledger.rs`
- `remove_entry(cohort, entity_id, type_id)` — removes one DashMap entry
- `drain_community_into(live, community_id) -> Vec<(EntityId, SignalTypeId)>` — ownership transfer via `DashMap::remove + insert`
- Status: COMPLETE

## T7: RematerializationEngine Worker
**File**: `tidal/src/cohort/rematerialization/mod.rs`
- `RematerializationConfig` struct
- `RematerializationHandle` with `shutdown()` and `Drop`
- `start(config) -> RematerializationHandle` — spawns `tidal-remat` thread
- `worker_loop`: polls queue every 500ms, executes jobs, exponential backoff on failure
- Status: COMPLETE

## T8: TidalDb Integration
**Files**: `tidal/src/db/mod.rs`, `tidal/src/db/rematerialization.rs`, `tidal/src/db/lifecycle.rs`
- Added `purge_job_queue`, `rematerialization_metrics`, `rematerialization_handle` fields
- Engine started in `from_parts()` when `config.data_dir` is Some
- Engine stopped in `shutdown_inner()` before WAL shutdown
- Interrupted jobs requeued on startup
- Public methods: `submit_purge_job`, `purge_job_status`, `rematerialization_metrics`
- Status: COMPLETE

## T9: Integration Tests
**File**: `tidal/tests/m9_purge_remat.rs`
- 6 tests: `submit_purge_job_returns_job_id`, `purge_job_status_pending_after_submit`, `unknown_job_id_returns_none`, `rematerialization_metrics_snapshot_is_valid`, `job_succeeds_in_persistent_mode`, `multiple_jobs_processed_independently`
- Status: COMPLETE

## Bugfixes Applied
- Fixed `purge_retracts_from_ledger` test in `cohort/purge.rs` (ancient timestamp caused full signal decay)
- Fixed `query/retrieve/types/tests.rs` direct `Retrieve` struct initializers missing `community` field
- Fixed `entities/community.rs` temporary drop while borrowed (DashMap entry)
- Fixed `ranking/executor/mod.rs` `if let Some` on `Result` (bootstrapped code used wrong arm)
- Replaced `uuid::Uuid` in `entities/revocation.rs` with `[u8; 16]` backed by timestamp+AtomicU64