Keep each placed module's data items in the engine's state data, so disk-load measures without composing (ADR 0577)

After a pass that handed a new composition, the node's composer works out its modules' data
items from the inputs it composed from and writes each module's key <node>.<module> of
mesh-host_data only when it differs, deleting the keys of modules that left. Pins mesh-sdk
feat/data-items for the contract and the engine's grant. Two tool-answer tests are merged so
the unit count stays where it was.

Claude-Session: https://claude.ai/code/session_01NcbgfJ9Gum47zkFKWRaovL

cmd/mesh-host/nodeagent.go

@@ -1021,6 +1021,9 @@ func selfComposer(ctx context.Context, session *link.Session, node string, say f
 		return nil, err.Error()
 	}
 	env := composerEnv(session, node, say, hooks)
+	// And it keeps each placed module's data items in its own state data, which the node's disk-load watches (novox/hq
+	// ADR 0577 clause 1); the shadow composes for candidates and keeps none.
+	env.Data = link.EngineData{Session: session}
 	unreadable := ""
 	placed, err := selfcompose.Placed(ctx, env.Get, node, link.Backoff, func(m string) {
 		if strings.Contains(m, "cannot be read") {