The router.SecureProvider interface previously required a public
IsSecure() bool method. Any test mock — or future production type —
could satisfy it by returning true, defeating the W1 "only wrapped
providers may flow past the boundary" contract through convention
rather than at the type level.
Replaces IsSecure() bool with an unexported security.Marker interface
that has a single secured() method. Go's method-set semantics key
unexported methods by their defining package, so only types declared in
internal/security can satisfy Marker. *SafeProvider gets the lone
secured() implementation; router.SecureProvider embeds Marker.
The seal forces every test mock that previously implemented IsSecure()
to either (a) be wrapped with security.WrapProvider(mp, nil) at the use
site, or (b) drop the method entirely if the mock never flows through
SecureProvider. 93 use sites across 11 test files were updated via a
per-package secureMock helper. WrapProvider with a nil firewall ref is
a no-op pass-through, so test behavior is unchanged.
Empirically: a type from outside internal/security can declare
`secured()` but the compiler will reject assigning it to
router.SecureProvider because the unexported method belongs to the
other package's namespace. Convention → compile-time guarantee.
vikingowl
fb42202834