Files
HealthLog/src/app/api/mcp
Marc-André Bombeck e9029ed3c2 feat(sharing): resolve the acting account inside the auth layer
One resolver, both transports, on every request. The cookie path reads
the carrier off the session row it has already loaded; the Bearer path
reads the `X-HealthLog-Account` selector header, because stamping switch
state onto a long-lived token would make the credential itself ambient
authority. Two carriers converge on one function for the same reason
`resolveBearerToken` lives in one file for two wires.

Three declared modes. `requireRecordAuth("read" | "write")` honours a
valid switch and substitutes the owner as the data scope while keeping
the delegate as the actor. `requireActorAuth()` always serves the
caller's own rows and keeps working under a switch, which is what the
switcher and the banner need.

Bare `requireAuth()` refuses to run under a switch at all, with a stable
`sharing.not_permitted` code. It does not fall back to the caller's own
account, and that arm is the point of the whole design: a delegate who
believes they are reading the owner's record and is handed their own is
the same data mixing pointed the other way. A route nobody has reviewed
is inaccessible while switched, never wrongly accessible.

The grant is loaded from Postgres on the request that uses it. Nothing
memoises the verdict, so a revocation lands on the delegate's next
request rather than their next login.

Refusals do not enumerate. The denial takes no constructor arguments and
carries a fixed message, and neither branch looks the named account up:
an account that does not exist and one that granted nothing produce the
same empty row from the same query, so the two answers are identical in
bytes and in timing rather than by careful wording. The reason reaches
the audit row and the wide event and nothing else.

`getSession()` still answers who is calling. That is what leaves
`requireAdmin`, `requireCookieAuth` and `requireFreshMfa` structurally
out of a switch's reach; the row's carrier rides out beside the session
id as a value to be checked, never as a decision already made.

The selector header is a Bearer carrier only. Sent over the cookie
transport, or to an actor surface, it is refused rather than ignored. A
client that names an account on a route which never reads one has a bug,
and a correct response to a wrong expectation hides that bug until it
arrives as a support case about data that looks wrong.

Five test files gain the session shape their fixtures always claimed to
have; they were building an auth context without one.
2026-08-02 11:32:00 +02:00
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