毫髮不差 The Demon Mirror Fails
玉帝即傳旨宣托塔李天王，教：「把照妖鏡來照這廝誰真誰假，教他假滅真存。」天王即取鏡照住，請玉帝同眾神觀看。鏡中乃是兩個孫悟空的影子，金箍、衣服，毫髮不差。玉帝亦辨不出，趕出殿外。玉帝即传旨宣托塔李天王，教：「把照妖镜来照这厮谁真谁假，教他假灭真存。」天王即取镜照住，请玉帝同众神观看。镜中乃是两个孙悟空的影子，金箍、衣服，毫发不差。玉帝亦辨不出，赶出殿外。
逐句解 Line by line
The Jade Emperor at once issued a decree summoning Devarāja Li the Pagoda-Bearer, ordering: "Take the demon-revealing mirror and shine it on these fellows, to see who is true and who false; make the false perish and the true remain."
The demon-revealing mirror is brought out — the one instrument in the cosmos designed to show a shape-changer what it really is. 教 appears twice with two jobs: first "ordered", then "make him". Both are jiào. 誰 takes the bookish shuí rather than the everyday shéi.
The Devarāja took up the mirror and held it steady upon them, inviting the Jade Emperor and the host of spirits to look together.
The whole court is invited to watch, which raises the stakes of what the mirror is about to show. 觀看 puts guān and kàn side by side, two characters that each carry more than one reading and are each pinned here.
Within the mirror were the reflections of two Sun Wukongs. Golden fillet and clothing — there was not a hair's difference between them.
毫髮不差, not a hair's difference. 差 is chā, difference, not the chāi of sending someone off on an errand — and because that makes it a first-tone syllable, the 不 before it stays bù rather than shifting to bú.
The Jade Emperor too could not tell them apart, and drove them out of the hall.
The fourth authority beaten, and the first to deal with the case by simply throwing it out of the building rather than passing it on.
The demon-revealing mirror is a different category of instrument from everything tried so far. The Bodhisattva looked, and looking failed; she cast the fillet spell, and the body failed to discriminate. The mirror depends on neither. It is built to show a thing's original shape regardless of what it is currently wearing — the closest the cosmos comes to a DNA test — and it is precisely the right tool for an imposture.
It shows two Sun Wukongs. This is the chapter's most important negative result, because it shuts off the obvious explanation. The false Pilgrim is not a disguised something-else; his original shape, the one the mirror exists to expose, is Sun Wukong. Whatever the answer turns out to be, it cannot be that somebody put on a costume — and the reader now knows this three thousand characters before the Buddha explains it.
毫髮不差 — not a hair's difference — is the phrase the chapter has been building toward, and it lands on the golden fillet, the one object in the cosmos fitted to one skull. The Jade Emperor's response is to drive them both out of the hall, which is less a judgement than an admission.