Sri Harry-ji ,
Is your question related to the authorship of
Dakṣināmūrtistotram ?
Is the question centred around whether S'ankarāchārya is its author or not?
Isn't your question "Does this metaphor of the world as an image in a mirror only appear in Kashmir Shaivite writings?" imply that if it isn't the distinct feature of Kashmir Shaivism,
Amarhath Rai's rejection of S'ankara's authorship on the basis of this image in the stotram is not tenable?
Till now , did you get any message confirming that it is the distinct feature of Kashmir Shaivism ?