Three follow-ups on the flat CRUD blueprints triggered by code-review +
spec-analyst (MA4, MA5, MA6).
**MA4 — `created_by_id`** — engagements, TTPs and scenarios now record the
creator from `current_user.id` instead of leaving the FK NULL. The new
`api._helpers.current_user_id()` exposes the UUID safely (returns None when
the request is unauthenticated, e.g. during /healthz).
**MA5 — Audit log integration** — `api._helpers.audit_write(...)` wraps the
hash-chained `AuditWriter` and is called after every successful commit in
the 4 blueprints (engagement / host / ttp / scenario incl. step), recording
the actor, action, resource type/id, IP, user agent, and small metadata
(field list, names, engagement scope). F13 "Toute mutation tracée" now
holds end-to-end.
**MA6 — RT operator scope on engagements** — F11 limits RT operators to
"engagements assignés". The previous implementation let them list / read
every engagement and every nested resource. Fix: `is_rt_lead()` short-
circuits the check for RT leads; otherwise a membership probe against
`engagement_member` runs on every list/read and on `_engagement_or_404` in
`hosts.py` and `scenarios.py`. Listings now `JOIN engagement_member` and
filter by `current_user.id`.
`audit_write` casts `db.session` (a `scoped_session` proxy) to the unwrapped
`sqlalchemy.orm.Session` that `AuditWriter` expects; the two are
interchangeable at runtime.
The promotion-perm check on TTPs no longer needs a lazy `flask_login` import
since the decorator scope already brings `current_user` in.
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