Validate command alias termination

internal/alias/machine.go

@@ -39,6 +39,7 @@ type Machine struct {
 	transitions map[transitionKey]transition
 	alphabet    []symbol
 	literals    map[string]struct{}
+	mappings    []Mapping
 }
 
 // Compile builds a finite stack machine with explicit lookup, restoration,
@@ -55,11 +56,15 @@ func compileMachine(resolver *Resolver) *Machine {
 	// Trie controls only move to child nodes. Helper controls prepend a fixed
 	// number of saved symbols and then halt or return to the trie root after a
 	// selected mapping has been completed.
+	// End and boundary symbols are only restored as the final item below any
+	// emitted command tokens. No transition places a marker above ordinary
+	// input, so each remains the unique bottom marker of a valid stack.
 	machine := &Machine{
 		start:       0,
 		halt:        len(resolver.trie),
 		transitions: make(map[transitionKey]transition),
 		literals:    make(map[string]struct{}),
+		mappings:    resolver.mappings,
 	}
 	for _, mapping := range resolver.mappings {
 		for _, path := range []commandpath.Path{mapping.Source, mapping.Target} {