Apple and GT Advanced Technologies Inc. struck an agreement yesterday that will let GT begin the shutdown of key Arizona operations, and shed some more light on why the former stock market darling abruptly filed for bankruptcy this month, Reuters reported yesterday. A lawyer for GT, Apple's erstwhile sapphire supplier, described the deal at a hearing in U.S. Bankruptcy Court in Springfield, Mass., saying that it would save the company money and allow it to be more open about its mysterious chapter 11 filing on Oct. 6. Scant details have emerged since the filing, which wiped out most of GT's market value and triggered speculation as to what might have soured its relationship with Apple. It remains unclear how much information GT would get to reveal under Tuesday's agreement, which was described verbally by GT's lawyer but has not been fully outlined in court filings.