أَيِ الظَّرْفِيَّةِ مُقَدَّرَةٌ بِالْفِعْلِ عَلَى الْأَصَحِّ
That is, the adverbial predicate is most correctly understood with an implied verb.
One account treats «fī al-dār» as attached to an implied verb such as «istaqarra»; another posits an implied participle such as «mustaqirr». Neither adds an audible word to the actual statement.
Taqdīr is an explanatory grammatical reconstruction; it should not be mistaken for silently altering the source utterance.