`SessionStore` has no concept of a caller, so authorization lives entirely outside it

[The-Running-Dev]

SessionStore has no concept of a caller, so authorization lives entirely outside it

getScene(sessionId) succeeds for anyone holding the id. Adventures added ownership guards
as Fastify preHandlers over its own profile_id columns, because the port gave it nowhere
to express the check. That is the right layering for a static demo and a real gap for a
hosted engine — it is the first concrete requirement the deferred NEaaS layer has produced.

Found by the first downstream host — see design/90-decisions.md, Found by the first
downstream host — SubZeroDev.Adventures.

Done when

• The contract records this as a deliberate layering decision — authorization is
  host-owned, SessionStore stays caller-agnostic — with a stated trigger for revisiting
  it once the deferred NEaaS/hosting layer is actually built.

---

Agent instructions

• Authority: this issue, since the bullet no longer lives in design/90-decisions.md's
  open register (Found by the first downstream host).
• Stop if: the decision turns out to require a real SessionStore signature change now,
  rather than a documented deferral — that's a contract change beyond what this issue scopes.