mesh-issues and mesh-knowledge: pin mesh-sdk at its merge of CallerOf; mesh-knowledge reads the caller from the runtime (hq issue 365)

Both pin mesh-sdk/go at 4cf45b5 (mesh-sdk#20 merged). mesh-knowledge's one
reading of the caller, callerOf, now answers stdio.CallerOf, so a call on the
caller-named subject is recorded as its caller's bus user and any other as
unproven, never from the arguments.

modules/mesh-knowledge/cmd/mesh-knowledge/main.go

@@ -103,11 +103,10 @@ func serve(k *KB, status string) {
 	}
 }
 
-// callerOf is who called, as the runtime proves it: the one place the caller is read, so the change that brings it
-// is this one function. The runtime does not hand a module its caller yet (hq issue 365): the SDK's tool call carries
-// a name and arguments only, so the SDK must first pass the runtime's proven caller to a tool. Until it does, every
-// caller is Unproven. It is never read from the call's arguments, so no caller can name another.
-func callerOf(map[string]any) string { return Unproven }
+// callerOf is who called, as the runtime proves it: the one place the caller is read. The tool runner takes the
+// caller's bus user from the subject the call arrived on and hands it through the SDK (hq issue 365); Unproven where
+// it proves none. It is never read from the call's arguments, so no caller can name another.
+func callerOf(args map[string]any) string { return stdio.CallerOf(args) }
 
 // hear subscribes to the router's word on this module's asks, asked again until the runtime takes it.
 func hear(k *KB) {