85028678c7
Task 3-3-01: POST /v1/assessment/grade (engine over DI; GRADED -> 200 full record;
UNGRADABLE_* gate outcomes -> 200 gate records with missing_seqs/integrity_flag —
never 5xx, they are valid results; persistent D-020 failure -> 502, nothing persisted)
+ GET /v1/assessment/grade/{learner}/{task} (404 unknown). GradeStore wired into
lifespan alongside TraceStore (single db_path, per-connection WAL). Unknown task POST ->
200 UNGRADABLE_EMPTY_TRACE (engine cannot distinguish absent from empty; gate record
persisted so POST->GET round-trips).
11 endpoint tests green; suite 283 green; ruff clean.
---ci---
phase: 3
milestone: v0.3
status: execute
requirements: {covered: [REQ-3-004], partial: []}
---/ci---