diff --git a/checker/types.go b/checker/types.go
index ee67132..ed4a9fc 100644
--- a/checker/types.go
+++ b/checker/types.go
@@ -220,24 +220,6 @@ type ObservationProvider interface {
 	Collect(ctx context.Context, opts CheckerOptions) (any, error)
 }
 
-// ObservationSharer is an optional interface an ObservationProvider can
-// implement to declare that its observation depends only on a subset of the
-// inputs and may therefore be shared across check targets.
-//
-// ShareKey returns a stable string derived purely from the inputs that affect
-// the result (e.g. the sorted IP set + ping count). Two collections with the
-// same ShareKey produce identical data; the host may serve one from the other.
-// Return "" to opt out (the host falls back to per-target caching).
-//
-// ShareKey MUST be a pure function of opts: no network, no I/O. The host calls
-// it before deciding whether to collect, possibly on the locally registered
-// provider even when actual collection is delegated to a remote endpoint.
-//
-// Detect support with a type assertion: _, ok := provider.(ObservationSharer)
-type ObservationSharer interface {
-	ShareKey(opts CheckerOptions) (string, error)
-}
-
 // CheckRuleInfo is the JSON-serializable description of a rule, for API/UI listing.
 type CheckRuleInfo struct {
 	Name        string                       `json:"name"`